Module 7 - Maintenance Practices.pdf
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Book No:
IR PART 66 CAT A M7
Lufthansa Resource Technical Training Ltd Cwmbran S. Wales
For Training Purposes Only Lufthansa 1995
Maintenance Practices IR PART 66 CAT A M7
Training Manual Fundamentals
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M7 MAINTENANCE PRACTICES
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M7.1 SAFETY PRECAUTIONS AIRCRAFT AND WORKSHOP
M7 MAINTENANCE PRACTICES SAFETY PRECAUTIONS - AIRCRAFT AND WORKSHOP
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S 8. Always read and adhere to safety notices. Safety precautions can be found throughout the AMM and also on notice boards. If you suspect a safety issue exists don’t ignore it, report it either to your quality personnel or a senior engineer. Some airlines have confidential feedback forms you can fill in if you wish to remain anonymous. S 9. Never indulge in horseplay as this can result in serious injury occurring to yourself or a colleague. S 10. If in doubt check. Never carry out a maintenance task if you are unqualified or unsure how to do it.
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It is important that an engineer does not endager themself or those around them as a result of their actions. This is a requirement in the UK under the Health and Safety at work act 1974, which deals with employers and employees responsibilities towards health, safety and welfare of personnel within an organization. The act is a legal document and failure to observe its contents can result in both fines and/or imprisonment. Most personal safety precautions should be common sense, however, every year people suffer serious injury or death in the workplace because people accidentally or deliberately fail to observe simple personal safety precautions. Some of the basic precautions are listed below: S 1. Never carry matches, lighters or other sources of ignition onto an aircraft. S 2. Never carry loose articles onto an aircraft, unless they are related to a work task you are carrying out. In this case ensure that only the correct amount of articles required for the job are taken to the aircraft and that they are tightly controlled. S 3. Always wear the correct protective clothing. It is the Employers responsibility to provide protective clothing, but it is the individuals responsibility to use it correctly. In addition to this, wearing of jewellery such as rings is not recommended as if the jewellery catches it could accidentally amputate a finger. Other precautions include not wearing metal studded footwear as they may generate sparks and avoid wearing loose clothing, such as ties, when working with machine tools. S 4. Always use barrier creams to protect your hands. This will protect your skin from harmful substances such as oils or greases, which can cause sensitisation or even dermatitis after prolonged exposure. After work thoroughly wash you hands and apply a refatting cream to prevent skin from drying out. S 5. Keep work areas clean and tidy. Not only will this reduce the risk of FOD, but it will also reduce slip and trip hazards. Employ walkboards to place over trailing cables S 6. Ensure good tool control is maintained at all times. Account for all your tools at the end of each working day. S 7. Never work on aircraft if you suspect you are under the influence of drugs or alcohol, or if you unfit for work due to being over tired.
PERSONAL SAFETY
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Reinforced footwear
Eye protection
Close-fitting high-buttoned overalls
Figure 1
Insulated soles
Cuffless trousers
No rings or watch
Closefitting cuffs
Ear protection Tidy hair style
Workshop and Hangar Safety
SAFE WORKING ENVIRONMENT
Keep workplace safe, efficient and tidy
UNSAFE WORKING ENVIRONMENT
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Head protection
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IN ORDER TO PREVENT POSSIBLE SPARKING DUE TO DIFFERENT ELECTRICAL POTENTIALS THE FOLLOWING PROCEDURE SHOULD BE ADOPTED WHEN BONDING AIRCRAFT AND REFUELLING VEHICLES. FIRSTLY ENSURE THAT BOTH THE REFUELLING VEHICLE AND THE AIRCRAFT ARE GROUNDED, THEN BOND THE REFUELLING VEHICLE TO THE AIRCRAFT BEFORE CONNECTING THE REFUELLING HOSE TO THE AIRCRAFT. WHEN DISCONNECTING, THE HOSE SHOULD BE DISCONNECTED PRIOR TO REMOVING THE BONDING LEAD
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Working in fuel tanks Before work is carried out on fuel tanks they should be drained and purged. Where work has to be carried out in fuel tanks a fuel resistant coverall should be worn along with suitable breathing apparatus. In addition a safety lookout, who has contact with the person working in the tank should be positioned outside the tank.
Fuel spillages Clear up all fuel using suitable equipment. If a major spill occurs, try to stop the fuelling operation, or cause of the leak. Evacuate personnel, call the fire service. Where possible stop the fuel from entering any drains and waterways using bunds, absorbent materials or emulsion compounds. All contaminated material should be disposed of in accordance with local regulations. All spills that enter drains and waterways should be reported to the local authorities.
CAUTION:
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Precautions when refuelling aircraft The following precautions should be observed when refuelling aircraft in order to minimize the risk of fire ’No Smoking’ signs should be displayed at a minimum distance of 15m (50’) from fuelling equipment and aircraft tank vents. A Fuelling Zone a MINIMUM of 6m (20’) from filling/venting points on both aircraft and fuelling equipment should be established prior to fuelling/defuelling operations. Within this zone S no electrical system should be switched on or off, and only those circuits necessary for the operation should be on. S Strobe lighting must not be on. S There must be no use of naked lights. This includes the engines of equipment/vehicles unless they have been designed for that purpose. S If necessary for the refuelling/defuelling operation, an APU (Auxiliary Power Unit) must be started prior to filler caps being removed or connections made. S GPUs (Ground Power Units) should be as far as practicable from aircraft fuelling points and vents. S Fire extinguishers should be at hand. S The aircraft should be earthed and bonded to fuelling equipment. S After the fuelling operation, bonding should not be removed until hoses have been disconnected and filler caps refitted. S Ground equipment must be moved away from the aircraft to prevent damage as the aircraft settles due to its increased weight. S Fuel bowsers will normally position themselves facing away from the aircraft being refuelled, for rapid emergency evacuation. A clear exit must be maintained. S Aircraft engines must not be operated. S People and vehicles within the fuelling zone must be kept to a minimum. S Fuelling is suspended during electrical storms in the vicinity.
FIRE-- GENERAL PRECAUTIONS
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Figure 2
M7 MAINTENANCE PRACTICES SAFETY PRECAUTIONS - AIRCRAFT AND WORKSHOP
Typical Fuelling/Defuelling Safety Zone
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CAUTION:
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IF YOU SUSPECT A PERSON HAS RECEIVED AN ELECTRIC SHOCK AND REQUIRES FIRST AID: ENSURE THAT THE PERSON IS NO LONGER IN CONTACT WITH THE ELECTRICAL SUPPLY. YOU MAY NEED TO CONSIDER SWITCHING OFF THE POWER SUPPLY AT THE SOCKET OR AT THE CIRCUIT BREAKER BOX. NEVER TOUCH THE VICTIM UNTIL YOU ARE SURE THEY ARE UNPLUGGED.
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Working with electricity When working with electricity it is important to take all safety precautions in order to ensure that serious injury and death are avoided. It is not the voltage of an electrical circuit that will kill a person, but the current. A current of as little as 0.1 Amp can be fatal! The following is a list of safety precautions that should be used as appropriate when working on aircraft electrical systems: S Ensure that external electrical power has been switched off. S Disconnect the aircraft battery. S Place warning signs at external power receptacles of the aircraft, advising personnel not to apply power. S Pull and tag all relevant CBs prior to work and ensure they are reset afterwards. S Prior to applying power, ensure all switches are in the correct position for the system they relate to. S General workshop and aircraft safety precautions include: S S Never handle or operate electrical equipment when you have either wet hands, feet or are stood in a wet area. S When working on aircraft the use of electrical power tools should be avoided. Instead Pneumatic tools are preferable whenever they are available. S Do not allow electrical wires and cables to dangle over sharp edges. S Always ensure that electrical cables are not frayed, and that they have undamaged insulation. S Never trail electrical wires through oil, water or other liquids S All equipment should have a suitable plug fitted and be either earthed, or where necessary, double insulated. S Electrical equipment needs to be checked regularly and a serviceable label attached with the most recent test date appended. S Only use approved and specially designed explosion proof electrical equipment in hazardous areas such as fuel tanks. S
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0.1AMP to 0.2AMP
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Figure 3
REACTION OF BODY TO 100 VOLTS
0.001AMP to 0.008AMP
MAY CAUSE 0.012AMP MUSCULAR to CONTRACTION 0.02AMP
MAY CAUSE SOME SENSATION
PATH OF CURRENT
Insulated mat
Work with one hand in pocket
Insulated soles
TAKE PRECAUTIONS WHEN WORKING ON LIVE EQUIPMENT
Working with Electricity
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EARTH (0 VOLTS)
ELECTRIC SHOCK
WILL CAUSE DEATH
240 VOLTS
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Compressed air in the workshop Compressed air is used in the workshop to provide operating pressure for pneumatic tools. The air is generally supplied at an operating pressure of approximately 80psi. When using compressed air supplies the following safety precautions must be adhered to: S Never point compressed air guns at people. S Never direct compressed air into skin, this can result in air entering the blood stream and may result in death. S Never fool around with compressed air supplies. S Always ensure that air hoses are in good condition and that the end fittings are correctly attached. S Always disconnect compressed air supplies when not in use.
Charging systems with compressed gases. Prior to charging systems with compressed gas purge the hose on the gas bottles as this will discharge contaminants to atmosphere rather than into aircraft systems. When charging aircraft systems ensure all connections are tight and increase the pressure in slow increments to ensure that the gas does not become hot and consequently give incorrect gauge readings. Always check that pressure gauges are within their calibration date this can be found on the calibration label ”due date”. Finally only charge to the pressure stated in the AMM or relevant technical documentation.
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Oxygen Oxygen is one of the three requirements for combustion to occur. It is therefore a very hazardous substance that can cause fire and explosion if mis-used. In order to avoid the risk of fire or explosion the following precautions should be observed: S Avoid oxygen coming into contact with oils and greases. Oxygen can cause oil and grease to spontaneously combust without the application of heat, therefore the use of oils and greases in oxygen systems is strictly forbidden. S Smoking immediately after working with oxygen systems should be avoided as clothing can absorb oxygen and the naked flame from a lighter or cigarette can then ignite the clothing. S Ensure correct tooling only is used on oxygen systems. Normal tooling can cause sparks and should not be used. S Sparks due to static electricity can ignite oxygen and so aircraft should be correctly bonded and earthed before working on oxygen systems. S If tooling such as gauges need lubricating, only approved lubricants can be used e.g. PTFE tape conforming to MIL SPEC T-27730. S Leak tests on oxygen systems should only use presscribed oil free solutions. S Before charging breathing oxygen systems on aircraft the oxygen should be smelt to ensure it is not contaminated. Charging of oxygen systems should be accomplished in accordance with the relevant AMM.
S Always disconnect compressed air supply to a power tool before replacing expendable components such as drill bits as this will prevent inadvertant operation of the tool.
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Working with compressed gases Compressed gases provide a number of potential dangers to personnel and as such should always be treated with extreme caution. Due to their very nature of being compressed in storage containers, gases contain extremely high levels of stored kinetic energy (rather like a compressed spring stores energy), if this energy is allowed to escape in an uncontrolled manner from it’s container, then it may cause the container to explosively decompress and rupture. For this reason containers used for storing compressed gases are lifed and must be within test dates when used. When not in use, compressed gas bottle should have protective caps fitted to protect integral valve assemblies.
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Figure 4
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Subsequent investigations revealed that the maximum pressure at the nozzle with the valve turned fully open was about 351 lbs, but the actual pressure at the time of the accident was much less - probably only a third.
The man was operated upon and blood transfusions given, but he died three days after being injured.
employees in a carpenters’ shop were using a compressed air hose to remove sawdust from their clothing. One man was seen to push the hose between the legs of a fellow-- worker from behind and the man sustained the following injuries: SBruising and bleeding in the area of the rectum; SShock; SAir through tissues over abdomen, chest and neck; SHernia canals in the groin ballooned with air; SAbdomen filled with air; SLower bowel torn open in three places, the longest tear being four inches; SAbdominal cavity filled with bowel material from lower bowel, also contained much fluid and blood; and SLining of abdominal cavity torn in several places.
Safety With Compressed Air
A South Wales man told how he thought he was going to die after one of his colleagues directed compressed air from an air line up his rectum in an ’act of horseplay’. Craig Warburton, of Cefn Hengoed, is accused of assault occasioning actual bodily harm on Philip Morgan at work in January last year. Mr Morgan told a jury at Cardiff Crown Court how he felt severe pain and a bubbling in his stomach before passing out. ’I thought I was going to die’, he told the court, ’I thought my insides were going to come away from me’. Mr Morgan told how employees at the factory, Conservatory Roof Systems of Caerphilly, often used to engage in acts of horseplay during quiet periods. ’There was name calling and bad language. Most of it was directed towards me.’ He said he was often the butt of the practical jokes because he worked in his own corner of the factory. ’I would sometimes retaliate, but the more I fought back, the worse it would be for me’. He said the workforce often took part in boisterous antics at quiet times, using reels of tape as Frisbees and firing screws from the compressed air lines. ’I was never given any training in the use of the air lines, but I received training in my previous job’, he told the court. The defendant is alleged to have placed the air line at the seat of Mr Morgan’s jeans and released the jet of air, with a pressure of 80 psi. Mr Morgan needed surgery after the incident and had to use a colostomy bag for several months before undergoing surgery again to reverse the colostomy. Warburton admits committing the act, but is denying the charge, claiming that Mr Morgan was a willing participant in the horseplay. The case continues.
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The Royal Society for the Prevention of Accidents, London, reports a serious case when
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Worker ’thought he was going to die’
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Safety Personal safety can be enhanced by taking certain sensible precautions. S Educate yourself about the properties (and any necessary safety precautions to take) of the substance you are dealing with. It is the employer’s responsibility to provide COSHH (Control of Substances Hazardous to Health) sheets, which provide important information for the user. Additionally information about all oils and chemicals used on aircraft can be found in the AMM chapter 20--31--00 S Minimise the possibility of combustion by -- wearing non-steel-tipped footwear -- not carrying matches or lighters. S Minimise the effects of fumes by -- wearing a suitable mask or respirator -- using a fume cabinet. S Clean up or contain (and cordon off) spillages promptly. S Prevent the contraction of dermatitis by -- applying barrier cream prior to work -- washing thoroughly after contact with oils and chemicals followed by the application of re-fatting cream -- using suitable protective gloves.
Working with oils and chemicals Oils and chemicals present several personal safety concerns. They can: S be inflammable S give off noxious fumes S present a slip hazard when spilt S cause skin disease (dermatitis).
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GLOVE BOX
Filter
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Figure 5
Pre-Filter
Work Surface
Fan
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VERTICAL FLOW
Pre-Filter
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Work Surface
Super-Interception Filter
CLEAN WORK STATIONS
HORIZONTAL FLOW
Fan
Super-Interception Filter
Clean Work Containers (Fume Cabinets)
Exhaust Grill
Fan
Filter
Fan
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HORIZONTAL FLOW
CLEAN WORK BOXES
Glass Panel
VERTICAL FLOW
Glass Panel
Filter Glass Panel
Fan
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Individual Lifting In the engineering industry it is often necessary to lift fairly heavy loads. As a general rule, loads lifted manually should not exceed 20 kg. Mechanical lifting equipment should be used for loads in excess of 20 kg. However, even lifting loads less than 20 kg can cause strain. and lifting loads incorrectly is one of the major causes of back trouble. The risk of personal injury and damage to equipment can be reduced by taking simple precautions before the lifting or handling operations begin. For example, if the load is obviously too heavy or bulky for one person to handle, you should ask for assistance. Even a light load can be dangerous if it obscures your vision. All moveable objects which form hazardous obstructions should be moved to a safe place before movement of the load commences. As has already been stated, it is important to use the correct lifting technique. This is because the human spine is not an efficient lifting device. If it is subjected to heavy strain, or incorrect methods of lifting, the lumbar discs may be damaged causing considerable pain. This is often referred to as a ’slipped disc’ and the damage (and pain) can be permanent. The correct way to lift a load manually is shown opposite. You should start the lift in a balanced squatting position with your legs at hip width apart and one foot slightly ahead of the other. The load to be lifted should be held close to your body. Make sure that you have a safe and secure grip on the load. Before taking the weight of the load, your back should be straightened and as near to the vertical as possible. Keep your head up and your chin drawn in; this helps to keep your spine straight and rigid.
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Team Lifting When a lifting party is formed in order to move a particularly large or heavy load, the team leader is solely responsible for the safe completion of the task. The team leader should not take part in the actual lifting but should ensure that: S Everyone understands what the job involves and the method chosen for its completion. S The area is clear of obstructions and that the floor is safe and will provide a good foothold. S The members of the lifting party are of similar height and physique, and that they are wearing any necessary protective clothing. S Each person should be positioned so that the weight is evenly distributed. S He or she takes up a position which gives the best all--round view of the area and will permit the development of any hazardous situation to be seen so that the appropriate action can be taken in time to prevent an accident. S Any equipment moved in order to carry out the operation is put back in its original position when the task has been completed.
To raise the load, first straighten your legs. This ensures that the load is being raised by your powerful thigh muscles and bones, and not by your back. To complete the lift, raise the upper part of your body to a vertical position. To carry the load, keep your body upright and hold the load close to your body. Wherever possible hold the load so that the bone structure of your body supports the load. If the load has jagged edges, wear protective gloves, and if hazardous liquids are being handled wear the appropriate protective clothing.
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Loads and Safety In the engineering industry, loads are defined as heavy and cumbersome objects such as machines, large castings and forgings, heavy bar, sheet and plate materials, etc., which have to be loaded onto vehicles, unloaded from vehicles and moved within the factory itself. The movement of heavy loads involves careful planning and the anticipation of potential hazards before they arise. When moving such loads it is important that you use the correct handling techniques and observe the appropriate safety precautions and codes of practice at all times.
Manual Handling
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Straighten legs to raise load
Let bone structure support load
Team leader positions himself to ensure appropriate action is taken to prevent an accident
Keep body upright and load close to body
Individual and Team Lifting
Each person should be positioned so that the weight is evenly distributed
Keep spine straight
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Figure 6
Everyone understands what the job involves
Keep back straight and near-vertical
M7 MAINTENANCE PRACTICES SAFETY PRECAUTIONS - AIRCRAFT AND WORKSHOP
Wear appropriate clothing
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Rubber or plastic boots
Rubber or plastic apron
Rubber or plastic gloves
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Working in Tanks When fuel tanks have been completely emptied, the fire risk is still present due to the presence of fuel fumes. Tanks should be thoroughly purged prior to entering them and ideally continually purged throughout occupation.Station an assistant outside the tank access to assist in a rescue if necessary.Always use flameproof torches when working in tanks.
Without any one of these components a frie can’t exist. Fire extinguishers work on the priciples of either excluding oxygen or removing heat from the fire. Fuel for fires is classified into for groups they are. S Class A fires which have wood, paper and fabric as fuels S Class B fires which have petrol oils and lubricants as fuels S Class C fires which are Electic fires S Class D fires which have metals as fuels You will already be aware of the potential fire hazards of working in an environment containing vast amounts of highly flammable fuel, such as that contained in aircraft.Because fire is a most dangerous threat which will always be with us the following precautions must be observed:Smoke only in designated areas set aside for that purpose.Observe and obey ’No Smoking’ signs on flight lines.Do not carry non-safety matches and do not wear steel tips on shoes, as they can create sparks.When operating petrol engined ground equipment, have a foam fire extinguisher handy.Flammable liquids like paints and dope should be kept in an approved store outside the hangar or workshop.If using heat torches in a workshop (such as blow lamps), the flame should be directed towards fire bricks when not in immediate use.You should find out where fire extinguishers and fire buckets are located in your place of work.
Fire safety Fires require three components in order to burn. S Heat S Fuel S Oxygen
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Figure 7
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Types of Fire and Relevant Extinguishers
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Dry Powder These extinguishers are most effective on Class B, C and particularly Class D (metal) fires. The two types of dry chemical extinguishers include one that contains ordinary sodium or potassium bicarbonate, urea potassium bicarbonate and potassium chloride base agents. The second multi--purpose type contains an ammonium phosphate base. The multi--purpose extinguisher can be used on class A, B, and C fires. Most dry chemical extinguishers use stored pressure to discharge the agent, and the fire is extinguished mainly by the interruption of the combustion chain reaction.
Carbon Dioxide Carbon dioxide extinguishers work by excluding oxygen from a fire, as well as rapidly cooling it. It is suitable to extinguish Class B fires, and because carbon dioxide is not electrically conductive, can also be used on Class C fires.
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Foam Foam fire extinguishers use an aqueous film forming foam (AFFF) agent that expels a layer of foam when it is discharged through a nozzle onto the surface of a burning liquid, starving a fire of oxygen. They also have a cooling action with a wider extinguishing application than water on solid combustible materials, and are therefore suitable for Class A and B fires. Firefighters spray a foam ’blanket’ onto runways when aircraft land ’wheels-up’ to suppress sparks as the aircraft slides along. AFFF, known asTridol, is a synthetic foam concentrate containing detergent and fluorocarbon surfactant that forms a foam capable of producing a vapour-suppressing aqueous film on the surface of some hydrocarbon fuels. It provides rapid flame knockdown on short preburn, shallow spill fires (eg aircraft crash fires), but is not suited for use on long preburn, deep--seated fires (eg storage tank fires). Developed in the 1960s, AFFF is today largely replaced by the more sophisticated FFFP, known as Petroseal, a natural protein--based foam concentrate containing fluorocarbon surfactants that forms a foam capable of producing a vapour--suppressing aqueous film on the surface of hydrocarbon fuels. It was developed in the 1980s.
Halogenated Hydrocarbon The most common fire extinguishing agent for aircraft cabin fires is Halon, a liquefied, compressed gas that stops the spread of fire by chemically disrupting combustion. It is most effective on Class B and C fires. It can be used on Class A and D, but is not as effective. While the production of Halon ceased on January 1, 1994 under the Clean Air Act, it is still legal to purchase and use recycled Halon and Halon fire extinguishers. In fact, the FAA requires all commercial aircraft to exclusively use halon. Halon 1211 and 1301 or ”Halon Blend” are liquefied compressed gasses which stop the spread of fire by chemically interrupting combustion. Halons are odourless, colourless, electrically nonconductive, leave no residue after use and are ”people safe.” The Halon blend is far superior to the 1211 Halon propelled by nitrogen because it generates its own pressure so that it does not change even if the extinguisher is almost empty. Halon 1211 is Bromochlorodifluoromethane (BCF). Halon 1301 is Bromotrifluoromethane.
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Water Water extinguishers work by cooling the fire below its kindling temperature. They should only be used for Class A fires, where electricity and chemicals are not present. Indeed, using water on a Class D fire can intensify the fire. The water is pressurised and propelled from the extinguisher by air or carbon dioxide.
Types of Fire Extinguishers
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Aircraft recovery A report will need to be written on the incident. One of the report’s aims will be to recommend actions to prevent a recurrence of the incident. Depending on the severity of the damage the CAA and manufacturers may be required. If damage is within limits stated in AMM/SRM the the aircraft can be repaired and returned to service. All accidents/incidents involving aircraft need to be reported to the Aircraft Accidents Investigation Branch (AAIB). This must be a written report, but a 24 hour hotline is also available
Aircraft/ engine fires In the event of an Aircraft/Engine fire S Where possible shut down all systems. Fuel, Engine, Electrical and Hydraulic S Call emergency services, try to tackle the blaze. S Organize First Aid and call for medical assistance. S Remove all equipment from the area. S Give technical assistance to fire service. S After fire is extinguished; recover aircraft
Fire in a building If the fire is small and an appropriate extinguisher is available it may be possible to try and put the fire out, but only if it is safe to do so. At the same time the local emergency services should be called (999 in the UK) on the appropriate number. Note that some airfields will have their own emergency numbers. If the fire can not be extinguished then the building should be evacuated, remembering to close all fire doors and where possible, hangar doors.
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Notify fire brigade
Sound alarm
Close door to confine fire
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Figure 8
Fighting Fires
If fire cannot be controlled, evacuate
If safe to do so, fight fire
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M 7.2 WORKSHOP PRACTISES
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Precision measuring and test equipment must, by definition, be accurate.
TOOL CALIBRATION
Personal Tools All personal tools should be marked by the individual so that they are traceable to him.
Tool Stores Tool stores will often have a system in place whereby all tools on loan to a tradesman will be accounted for by tagging. A tool tag (or ’tally’) belonging to the tradesman will be exchanged for the tool and placed on the spot vacated by the tool (tools are often held on “shadow boards“ for easy checking). In this way, it can be quickly established that a tool is missing from the store and who booked it out. This is to prevent the theft of tools, but also (and more importantly) to minimise the chance of the tool being left in the aircraft, becoming a potential loose-article hazard.
As stated in the previous section, FOD is preventable. Tool control must be stringently applied by the tradesman, and the work area diligently checked for any tools or FOD at the end of a job or work-shift.
TOOL CONTROL
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Safety in the aircraft business is judged to be of the utmost importance. Lives depend on the aircraft performing as designed, transporting people and cargo safely from A to B. As an engineer, maintaining people’s confidence in this safe performance starts with your attitude to your work. There can be no half-measures with aircraft maintenance and repair procedures are developed precisely so that servicing is carried out correctly and safely and must not be deviated from without express permission or concession from the designers. It is vital that the aircraft engineer applies the highest standards of workmanship at all times. The aircraft engineer is constantly under pressure to complete work quickly. Always remember that there is always time to do the job properly. Do it wrong and you may not have anything to correct. Would you be happy and confident to fly on an aircraft that you have worked on?
STANDARDS OF WORKMANSHIP
Use of Precision Measuring and Test Equipment When using precision measuring and test equipment, ensure that a calibration certificate accompanies the tool and that it is within its calibration due-date. If desired, record the equipment’s details and calibration information on the job card.
To be able to rely on the equipment’s accuracy, it must itself be checked (calibrated) periodically. Standards for calibration are laid down by the authorities, and companies performing the calibration must meet exacting criteria. Equipment in what is considered normal use will be subject to annual calibration, but frequent-use equipment will be calibrated more frequently.
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A good tradesman looks after his tools. Good tools are expensive and should be treated with respect. They will let you down only if neglected. If they fall into disrepair, they lose their effectiveness and are potentially dangerous. Always keep tools in a serviceable condition: S Lubricate them regularly to prevent corrosion and seizing up. S Inspect them before use for any damage (cracks, splits, rounding-off of edges, bluntness etc). Damaged tools beyond repair should be destroyed. The temptation is always to keep them for use as specially-adapted tools, but there is invariably a tool manufactured and available for the job, so resist the temptation.
TOOL HUSBANDRY
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Figure 9
Tool Control
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Storage Aircraft supplies should be stored in clean, well-ventilated premises maintained at an even dry temperature to minimise the effects of condensation. Very often, the manufacturer will specify the ideal conditions. All materials of a flammable nature (dope, thinners, paint and other solvents) should be stored in an area isolated from main buildings. Items that can adversely affect other items should be segregated: S acid should not be placed whereby its fumes may affect raw materials or finished parts S phenolic plastics should be segregated from cadmium-plated steel parts S magnesium alloys should not be stored with flammable materials.
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Environment Take care of your environment. Dispose of waste according to local instructions in approved containers. Recycling should always be encouraged.
Care Care should be taken with all material used in the workshop. Scratches in metal surfaces are stress-raisers that can initiate cracks or corrosion.
Identification All materials in storage should have sufficient information attached to them to provide an audit trail, ie they can be identified to a manufacturer’s batch. Sheet aluminium alloy is normally stamped with the relevant information in one corner, whilst sheet steels usually have a stamped tally attached to one corner. This information should be copied to work documents.
Stock should remain in its delivery packaging as long as is practicable. Materials in long lengths (extrusions, tubes, bars etc) should be stored vertically, thereby reducing the risk of bowing and handling damage. All pipe and hose assemblies should be stored with their ends blanked to prevent ingress of dirt. Hoses should be uncoiled. Tyres should be stored vertically in special racks embodying tubes that ensure each tyre is supported at two points, reducing distortion to a minimum. They should be rotated every two or three months and any delivery wrapping should be kept in place. Sheet metal should be stored on edge in racks clear of the floor with transport protection (grease, paper or plastic coating) left in place. Flat stacking is not recommended to minimise scratching. Metal bars and tubing should be stored in racks either horizontally (well-supported along their length) or vertically. Fasteners (nuts, bolts, rivets etc) should be kept in their delivery packaging (with their identification labels) as long as possible prior to use. This is a safety issue; it reduces the possibility of an incorrect item being fitted if it is clearly identified.
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Safety Workshops, by their very nature, contain a variety of items that may S be heavy S be sharp S be toxic S give off noxious fumes S deliver electric shocks S burn S irritate the eyes etc. The list is seemingly endless, but it is important to S recognise that workshops are potentially dangerous places S know how to minimise the risks. Personal protective apparel has been covered in the previous section, but it is also important to look after the materials themselves. “The correct handling of materials, especially the high strength aluminium alloys, is of extreme importance. Great care is necessary during loading and unloading and storage at the consignee’s works to ensure that the material is not damaged by chafing, scratching, bruising or indentation, and that it is not excessively strained by bending, otherwise the mechanical properties of the material may be seriously affected. Heavy forgings, extrusions and castings should be carried and stored singly, ensuring that there is adequate support to maintain the material in its intended shape without strain.
USE OF WORKSHOP MATERIALS
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Figure 10
Typical Equipment Stores
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Introduction In order to arrive at values of distance, weight, speed, volume, temperature, pressure etc., it is necessary to be familiar with the accepted methods tor measuring these values and the units used to express them. Through the ages, human beings have devised many methods for measuring. However, it would be impossible to cover even a small part of the information accumulated over these several thousand years. Measurements used today in aviation are the English (Imperial) system and the SI (metric) system. SI is the abbreviation for the Système International d’Unités, the modernized version of the metric system that the USA and other nations have agreed to use.
GENERAL
DIMENSIONS, ALLOWANCES & TOLERANCES
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Figure 11
Measurement Examples
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Dimensional Tolerances A general tolerance is usually given for all dimensions on a drawing and is stated in a printed box on the drawing. When the general tolerance is not appropriate, an individual tolerance may be given to a dimension. As shown below, tolerances may be expressed by:-S quoting the upper and lower limits, or S quoting the nominal dimension and the limits of tolerance above and below that dimension.
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Allowance Parts that have a maximum and minimum allowable size are still considered acceptable if their size falls within the range given. The difference between the nominal dimension and the upper or lower limit is called the allowance. For example, if a dimension is depicted as .3125 inches +/- .0005, the allowable dimensions are between .3120 and .3130 inches.
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Measurement of Dimensions Measuring of material and machined subjects involves the use of measuring tools to determine sizes of length, width, thickness, diameters etc.
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Thickness
Width
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Figure 12
Length
Measurement Of Dimensions
Diameter
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English System The majority of people in English--speaking countries are familiar with the English unit system. Its units of length, time and weight are the inch, second and pound. Therefore the complete documentation of Boeing aircraft uses the English unit system. Airbus documentation uses both Imperial and metric units.
Metric System The International System of Units, known as the SI system, had its origin when the metre was selected as the unit of length and the kilogram as the unit of mass. These units were created by the National Academy of Science and adopted by the National Assembly of France in 1795. The United States Congress legalised the use of the metric system throughout the United States on July 28, 1866, but it was not until December 23, 1975 that the metric Bill was signed into law in the United States to convert all measurements into the metric system. One of the great advantages of the metric system is the fact that it is built on decimal units. Each basic unit may be multiplied or divided by ten as many times as it is necessary to get a convenient size. Each of these multiples has a definite prefix, symbol and name.
MEASUREMENT UNIT SYSTEM
Di
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Figure 13
Number Prefix Table
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= 9/5 (0C + 32) = 5/9 (0F -- 32)
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2. ?0F = 270C 27 x 9/5 + 32 = 270C 80.60F = 270C
Conversion Examples 1. ?0C = 630F 5/9 (63--32) = 630F 5/9 x 31 = 630F 17.20C = 630F
0C
0F
Fahrenheit / Celsius Conversion To convert one type of scale to the other we use the following formula:
Water boils 1000C Ice melts 00C Absolute zero --2730C
Celsius unit In the metric system the temperatures are given in degrees Celsius.
Water boils 2120F Ice melts 320F Absolute zero --4600F
Fahrenheit Unit In the English / American unit system all temperatures are given in degrees Fahrenheit.
Temperature Unit Temperature is the degree of heat or cold measurable in a body. The measurement is accomplished with a thermometer and the value is expressed in degrees Fahrenheit or Celsius.
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Boeing Dimensioning System All linear dimensions on Boeing drawings are in inches and decimal fractions, enabling the designers to clearly specify the degree of accuracy required for a given dimension. The Boeing system of dimensioning, the decimal system, is in units of tens, hundredths, thousandths, ten thousandths (1’s, 10’s, 100’s, 1,000’s, 10,000’s) and so on. Each unit, when multiplied by ten, falls into the category of the next larger unit or, when divided by ten, into the next lower unit. Decimal fractions may seem rather difficult at first, but in reality they are much simpler than common fractions. Decimal fractions work in units of ten, the same as whole numbers. However, decimal fractions are always on the right side of the decimal point. Whenever numbers follow the decimal point, they represent measurements smaller than one inch. The first number after the decimal point is in tenths of an inch. There are ten tenths in an inch. The second number after the decimal point is in hundredths of an inch. Since the second number in 0.12 falls into the hundredths category, the entire dimension must be read in hundredths; that is, twelve one hundredths of an inch. A dimension is read in terms of the smallest unit shown; therefore 0.0015 is read as fifteen ten thousandths of an inch, or one and one--half thousandths.
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English Length System Originally the units inch, foot, yard and mile were not exact multiples or factors of one another, but for the sake of convenience the foot was made equal to 12 in, the yard was made 3 ft and the mile was made 5,280 ft or 1,760 yds. It is said that the inch was the width of a thumb, the foot was the length of a human foot and the yard was the distance from the tip of the nose to the tip of the thumb when the arm was extended to the side with the thumb pointing forward and the head faced forward. The mile was originated by the Romans and represented 1,000 paces, each pace being two steps (or 5 ft). This distance was later changed to 5280 ft, which is the present statute mile in both Great Britain and the United States. The nautical mile, used internationally for navigation, is based on 1/60 of one degree of the earth’s circumference at the equator. It is approximately 6,080 ft, or 1,853.2m. Many other units of length measurement have been used in various countries including the rod, fathom and league. All these units were established to meet particular needs within different areas. Because of the increase in travel, international commerce and scientific exchanges, there was a need for the standardisation of measurements. This has taken place through the use of the metric system.
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1 INCH
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Figure 14
English Length System
YARD
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One metre is equal to 39.37 in, which is a little longer than the U.S. yard. Thus 1 decimetre (dm) is equal to 3.937 in. In practice the units of length most commonly used are the millimetre, the centimetre, the metre and the kilometre.
10 millimetres = 1 centimetre 10 centimetres = 1 decimetre 10 decimetres = 1 metre 10 hectometres = 1 kilometre
Metric Length System The basic unit of measurement in the metric system is the metre. The length of a metre is based on a distance equal to one ten--millionth of the distance from the equator to the poles measured along a meridian, the meridian being the shortest distance along the earth’s surface and at right angles to the equator. This distance is equal to 1,650,763.73 wavelength of the orange-red light of excited krypton of mass number 86. Thus we see that the metre is based on a sound reference that will always be approximately the same. In order to provide an exact reference metre for scientific purposes, a bar of platinum--iridium was inscribed with two lines exactly 1m apart at the freezing point of water (320Fahrenheit (F) or 0_Celsius (C)). The International Metre bar is kept at the Bureau of Weights and Measures near Paris. Copies of this bar have been made and are kept in depositories in all the principal nations. In the metric system, all measurements of length are either multiples or sub-divisions of the metre based on multiples of 10. The following table shows how the units of length are related:
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Figure 15
Metric System
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1 in = 25.4 mm
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= 3.968 mm
= 7.92 mm
5/32 in
0.312 in = 25.4 x 0.312
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= 4.826 mm
= 9.525 mm
3/8 in
0.190 in =
= 7.935 mm
5/16 in
= 4.038 mm
= 4.76 mm
3/16 in = 25.4 16 x 3
0.159 in = 25,4 x 0.159
= 3.18 mm
1/8 in =25,4 8
= 29.21 mm
= 6.35 mm
1/4 in = 25.4 4
1.15 in = 25.4 x 1.15
= 12.7 mm
1/2 in = 25.4 2
Conversion Examples
So for sheet metal work it is essential to know the conversion between metres and inches because all hole sizes, material gauges, all dimensions etc. are given in inches and often need to be converted to the metric system.
Unit Conversion P!ease remember:
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13/64
11/64
9/64
7/64
5/64
3/64
1/64
Figure 16
7/32
5/32
3/32
1/32
Inches 0.379 0.794 1.191 1.588 1.985 2.381 2.778 3.175 3.572 3.969 4.366 4.762 5.159 5.556
Millimeter Equivalent
Decimal And Metric Equivalent Of Inches
3/16
1/8
1/16
0.0156 0.0313 0.0469 0.0625 0.0781 0.0938 0.1094 0.1250 0.1406 0.1563 0.1719 0.1875 0.2031 0.2188
Decimal Equivalent
DECIMAL AND METRIC EQUIVALENT OF INCHES
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General Steel scales or steel rules are found in almost all toolkits in both 6-- and 12-inch lengths. They are used for sheet metal layout and for making measurements where the accuracy of a vernier or a micrometer is not needed. Theses scales are made of either tempered carbon steel or of satin--finished stainless steel. They may be graduated in either the fraction or the decimal system of English or in metric measurements, with some scales having graduations in both systems. Fractionally graduated scales usually have one scale divided in increments of 1/32 inch and the other in 1/64 inch increments. Decimal scales have one scale in 1/10 or 1/50 of an inch and the other scale in increments of 1/1,000 inch. Metric graduations are in centimetres and millimetres. Scales are available in both the flexible form (about 0.015 inch thick) and the rigid form (about 0.040 inch thick).
RULES AND SCALES
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Figure 17
Flexible Scales
6 INCH FLEXIBLE SCALE
12 INCH FLEXIBLE SCALE (CHESTERMAN)
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Scale Handling When taking measurements with a scale, it should be so held that the graduation lines are as close as possible to the face. The eye which is observing the reading should be as near as possible opposite to the mark being read, to minimise the possibility of parallax error.
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Figure 18
Scale Handling
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Flexible Steel Tape The flexible steel tape is a very useful instrument for taking measurements up to several feet. The steel tape is equipped with a hook on one end so that it will hold onto a corner or ledge, thus making it possible for the rule to be used by one individual. The hook is attached to the tape with rivets and is slotted to allow it to move slightly to account for its thickness in calculations. Most steel tapes are graduated in English and metric measurements.
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Figure 19
Flexible Steel Tape
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Set Square The set square is the most common tool for testing squareness. When using the square, care should be taken to ensure that its blade is held perpendicular to the surface being tested or errors may occur.
SQUARES AND GAUGES
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External Squareness Measurement
Figure 20
Set Square
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Internal Squareness Measurement
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Radius Gauge Radius gauges are used to measure either inside or outside radii. Find a blade that fits the surface being checked.
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Outside radius
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Figure 21
Radius Gauge
Inside radius
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Radii of the work are too large
Radii found okay
Radii of the work are too small
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Protractor The protractor consists of an adjustable blade with a dial that is graduated from 0o to 180o. To use a protractor, set the blade to the angle being checked and lock the nut. The angle is indicated on the protractor head. The protractor is generally used in assembly areas to check part flanges or to verify jig--located angles, clips, etc.
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Figure 22
Protractor
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Thickness (Feeler) Gauge The feeler gauge is made up of a number of thin steel leaves that fold into a handle like the blades of a pocket knife. The thickness in thousandths of an inch or in hundreds of a millimetre is marked on each leaf. The marked leaves are inserted into a gap until the closest fitting leaf is found. The thickness of that leaf represents the size of the gap. The gauge is generally used in assembly areas to check interface gaps or gaps under bolt heads or nuts.
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Figure 23
Feeler Gauge
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Blend Out Measurement Sequence With A Feeler Gauge (Ref. NDT A3 10) 1. Put the straight edge on to the inspection area. 2. Measure the gap between the straight edge and the structure with the leaves of the feeler gauge. Make sure that the gauge touches the straight edge and the structure. 3. Write down the measurement by adding the respective feeler gauge dimensions.
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Figure 24
Feeler Gauge
Gap
✘
Feeler Gauge
Blend Out Measurement Sequence
Skin
Skin Straight edge flat on skin
✔
A-A
SECTION
Straight edge
Straight edge
Area where paint must be removed
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Ball (or hole) gauges are devices that are fitted into a hole and adjusted to fit the hole snugly. The gauge is then removed from the hole (taking care not to disturb the gauge setting) and its diameter measured (eg with a micrometer) to determine the hole’s size.
BALL GAUGES
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Adjustable end
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Figure 25
Ball (Hole) Gauges
Set has variety of diameters
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General Marking out means marking on the material all the lines and points which are needed to work with. In general this will be done in accordance with a dimensional drawing. This is a drawing showing the exact shape with all dimensions indicated. Take a piece of material and accurately copy the given dimensions of the work from the drawing. Then cut out the piece of material with the work marked out on it.
MARKING OUT AND TOOLS
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Figure 26
Marking Out Sequence
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Dividers Dividers are used for scribing arcs and circles, for measuring between points and for transferring dimensions taken from a steel rule. The contacts are the sharp points of the straight legs, and measurement is by visual comparison. Dividers are difficult to use accurately when the legs are widely extended and the points steeply inclined to the work surface. Dividers or compasses should not be used when marks or reference lines are drawn on metal skin surfaces, since the metal points will cause permanent damage. Instead, pencils are commonly used to mark out skins.
Tri-Square For squaring and for lines at right angles a tri-square is used.
Rule For marking out length, a rule or steel tape is used.
Marking Out Rules S Never use a lead pencil on titanium. The carbon, when heated, can infuse the metal and cause cracking. S When using a scriber or pencil with a straight edge, hold it at a slight angle so that the line will be parallel and as close as possible to the straight-edge. S For marking of aluminium alloy use only a soft lead pencil (except for cutlines, when a scriber may be used). S Mark only thin lines. S Mark lines only once.
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Rule
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Figure 27
Marking-Out Tools
Tri Square
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Dividers
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A SCRIBER IS USED ONLY WHEN THE MATERIAL WITHIN THE SCRIBED LINE IS TO BE CUT OUT AND THE SCRIBE MARK IS REMOVED AS PART OF THE SCRAP.
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Pencil When working with aluminium alloy, a soft lead pencil may be used for layout work or for marking reference lines in areas that will not be removed. However, using normal lead pencils on bare aluminium alloy can scratch the surface and introduce graphite into the material, resulting in corrosion. Three examples of acceptable commercial pencils are Stabilo 8008, Dixon Phano and Blaisdell, which use soft wax-charcoal in lieu of graphite.
NOTE:
Scriber The scriber is used to mark lines on metal surfaces.
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Scriber
Figure 28
Marking-Out Tools
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Pencil
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Combination Set The combination set is an elaboration of the steel rule. It consists of a rule with three heads; the stock (or square), the centre and the protractor. These heads slide along the scale and are removable.
M7 MAINTENANCE PRACTICES WORKSHOP PRACTISES
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simple clinometer
When used with rule, forms a
4 Protractor Head
1 Rule 2 Square Head 3 Centre Head
M7 MAINTENANCE PRACTICES WORKSHOP PRACTISES
Clamp 90o
45o
Figure 29
Clamp
Parallel and Scribing
Centre Line of Disk
Uses of Combination Set
face ’A’ is plumb
Spirit level ascertains
Depth Gauge
Tri Square and Height Gauge
45o
Spirit Level
Scriber
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Mitre 45o
45o Angle Gauge
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M7.3 TOOLS
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Pin Punch Pin punches have a parallel shank and the diameter is sized to match rivet shanks. The matching size punch is selected for the diameter of rivet being punched out. During this operation, the structure should be supported (normally with a riveting block) on the opposite face to prevent damage and minimise ’bounce-back’.
Starting (Taper) Punch This is used to start when driving out a bolt or pin. Once the taper almost fills the bolt-hole, the job should be finished with a pin punch.
Automatic Centre Punch An automatic centre punch incorporates an adjustable spring-loaded trip mechanism, negating the requirement for a hammer.
Centre Punch A centre punch’s tip is ground to an angle of approximately 60o and is used to make indentations in metal. This helps to prevent ’wander’ when starting to drill a hole. Care should be taken not to distort the surrounding material by using too agressive a blow.
Composition Punches are generally composed of steel, but can also be made of copper or bronze (to minimise damage to the object being drifted out).
Safety Eye protection should always be worn when a punch is used.
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Looking After Punches Over a period of time, the end of a punch (particularly the softer metals) will become burred over from repeated hammer blows. This burr can eventually split and small chips fly off; potentially a safety hazard. The punch end should be ground back to its original shape. Use a hand-file for the softer materials.
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Introduction Punches concentrate the force from a hammer blow to the immediate area of the punch tip.
PUNCHES
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Centre Punch
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Taper Punches
Figure 30
Punches
Pin Punches
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✔
✘
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Introduction Sawing is mostly used for separating material but also for producing grooves and notches. A saw blade has many teeth. Their cutting edges are shaped like a chisel. When sawing, at any time more than one tooth must be in contact with the workpiece. The teeth remove small chips of the material. The teeth must point in the cutting direction. NB The blade fitted in the junior hacksaw has the teeth facing towards the handle; the cutting direction is towards the operator. This is because the saw frame is springy and compresses the blade if force is applied as the saw is pushed away. The blade subsequently buckles.
SAWING
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wing nut
adapter guide
Figure 31
saw blade
blade adapters
frame
Saw
cutting direction
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handle
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Clearance To prevent the saw blade from binding as it cuts into the material, the slot it creates must be greater than the blade thickness. The saw blade, therefore, must cut the required clearance. This is accomplished by either of the following: S The teeth are set. S The blade is waved.
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Pitch The pitch is the space from one tooth to the next. Saw blades are rated depending on the number of teeth per one inch of blade length: S Coarse: for soft materials S Medium: for normal materials S Fine: for hard materials
SAW BLADE
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32 teeth
25 (1 inch)
22 teeth
25 (1 inch)
14 teeth
25mm (1 inch)
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Fine
Medium
Coarse
Figure 32
Saw Blade
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Waved blade
clearance
Teeth are set
clearance
view
bottom
view
bottom
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Guiding the Hacksaw Cutting is achieved mostly by arm movement. Moving the body assists the process. To produce a good cut, start the cut by holding the saw at an angle. S Forward stroke under pressure. S Return stroke without pressure. Use up as much of the blade length as possible. Near the end of the cut, just before the material separates, reduce the pressure on the saw.
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return stroke without pressure
Figure 33
Sawing
angle
tooth gap
cutting direction
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chips
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cutting stroke with pressure
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Introduction Filing is a process which removes material from metal or wood, etc. Filing can be : S A rough process to alter the size and shape of a part by removing a considerable amount of material. S A finishing process to smooth a surface without removing much material.
FILING
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Figure 34
handle
tang
blade
tip
File Parts
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Half-round files Half-round files are used to file medium and large radii.
Round files Round files are used to file small radii.
Square files Square files are used for filing keyways and for enlarging square or rectangular holes.
Triangular files Triangular files have a cross-section that is an equilateral triangle. These files are limited to internal angles greater than 60˚.
Flat files Flat files are used for flat or convex surfaces.
General The selection of the file shape depends on the size and shape of the surface to be worked.
FILE SHAPES
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SQUARE
FLAT
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Figure 35
File Shapes
HALF ROUND
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ROUND
TRIANGULAR
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Curved-Tooth A curved-tooth file (often called a ’Dreadnought’) is used to produce a very smooth finish on soft metals such as aluminium.
Rasp-Cut A rasp-cut file produces an extremely rough cut and is used on very soft materials such as wood and leather.
Double-Cut Double-cut files are used for fast metal removal and where a rough finish is permissible.
Single-Cut Single-cut files are generally used to produce a smooth surface or to file a keen edge. Also for use on soft metals like lead, zinc or aluminium.
S S S S
Smooth Second Cut (not to be confused with Double-Cut) Bastard Rough
General Files are also graded by the type, or grade, of finish they produce:
General File cuts are divided (with reference to the character of the teeth) into single-cut, double-cut, rasp-cut and curved-tooth.
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GRADE OF CUT
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FILE CUTS
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Single Cut
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Smooth
Bastard
Figure 36
File Cuts
File Grades
Second Cut
Double Cut
File Types
Rough
Rasp
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Curved (Dreadnought)
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Safety Always ensure a file in use has a handle fitted - the tang can puncture your hand.
Holding the file Hold the handle with your right hand so that the end of the handle presses against the palm. With the palm, or fingertips, of your left hand press down on the file tip. Left handed persons should hold the handle in their left hand and press on the file blade with the right hand.
Bench Vice Bench vice adjustment is important to achieve a proper working position. The bench vice should be 5--8 cm (2--3 inch) below your elbow (see picture).
PROPER WORKING POSITION
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Figure 37
5--8 cm 2--3 inch
Working Position
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(Ensure handle fitted for safety)
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Soft Metals However, when filing very soft metals (such as lead or aluminium), pressure should be applied on both forward and backward strokes. This has the effect of dislodging chips from between the file teeth, preventing clogging.
Pressing on the File With your right hand push the file along the longitudinal axis and press it down; with your left hand only press it down. Left handed persons vice versa. Apply pressure on the forward stroke only. Return the file without pressure.
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General Guide the file by moving your body evenly. Move the file in the direction of its longitudinal axis in order to avoid burrs in the work surface.
FILE TECHNIQUE
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Figure 38
File Technique
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Filing of concave radii The radius of the file must be smaller than the radius to be filed. Guide the file straight as if a flat surface is to filed, but turn the file about its longitudinal axis at the same time. To produce an even radius it is necessary to advance the file sideways. To prevent burrs, do not feed sideways .
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Filing of convex radii In order to obtain a radius, flat surfaces are filed until they approximately form a radius. The file is moved in the longitudinal direction and up and down at the same time. The position of the work in the vice has to be changed frequently in order to produce an accurate radius.
FILING OF RADII
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Figure 39
up and down motion
flat surface
Filing of Radii
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General For a final finish, you can use the draw filing process. This process is often used on parts that are long relative to their width, for example aluminium sheet’s edges. This procedure is used to get a fine surface on the edges to prevent crack growth.
DRAW FILING
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1
Figure 40
cut on forward stroke only
Draw Filing
start of stroke
finish of stroke
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General Files need to be cleaned frequently. A dirty file cannot produce a good finish and acts like a dull file. You can clean a file with a file brush by brushing across the file in a direction parallel to the teeth.
CLEANING DIRTY FILES
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Figure 41
Cleaning Dirty Files
Cleaning with file brush
File brush
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Introduction Technicians are often faced with the requirement to drill accurately-sized round holes in order to make attachments and to join parts of an assembly. The tool usually used for drilling such holes is the spiral-- or twist-drill. The steel drill usually consists of a cylinder into which has been cut spiral grooves or flutes. One end is pointed and the other is shaped to fit a particular drilling device such as a hand--drill. Drills are made of both carbon steel and high speed steel (HSS). The carbon steel drills cost less, but they will overheat and lose their hardness when they are used to drill very hard or tough material. For this reason, HSS drills are by far the most economical for use in aviation work. There are several types of drills available, so generally we have to use different drills, drill speeds, cutting agents and pressure for different materials.
GENERAL
DRILLING
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ss
Figure 42
Included angle
Lip angle
Cutting edge (lip)
Twist Drill
Lip relief or heel angle
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Margin The cylindrical portions of the land which is not cut away to provide clearance.
Flutes Helical grooves cut or formed in the body of the drill to provide cutting lips, to permit removal of chips and to allow cutting fluid to reach the cutting lips.
Land The land is the peripheral portion of the body between adjacent flutes.
Cutting edge The point of a drill includes the entire cone--shaped cutting end of the drill. The point includes the cutting edges, or lips, which are sharpened when the drill is ground. The web is the portion of the drill at the centre along the axis. It thickens nearer the shank. The web may also be defined as the material remaining at the centre of the drill after the flutes have been cut out. The web forms the dead-centre tip at the point of the drill. The dead--centre is in the exact centre of the tip and is on the line forming the axis of the drill.
Body The body of a drill is the part between the point and the shank. It includes the spiral flutes, the lands and the margin. The body is slightly tapered, being fractionally larger in diameter at the tip than at the shank, thus causing it to bore a hole with clearance to prevent the drill from binding.
Shank The shank of a drill is the part designed to fit into the drilling machine. It may be a plain cylinder in shape, which is designed for use in a drill chuck on a drill motor, pillar drill or hand drill. The drill shank may also be tapered or pyramid-shaped. The tapered drill shank is usually used in pillar drills. The pyramid--shaped shank is also called a bit shank and is designed to fit a hand brace such as that used for wood bits.
TWIST DRILL NOMENCLATURE
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Shank
Figure 43
Margin
Twist Drill Nomenclature
Land
Body
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Flute
Lip or Cutting Edge
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Extension drill The extension drill has a long shank for reaching limited--access areas. The drill should not be used unless absolutely necessary. Use a drill guard (a plastic tube slipped over the drill to protect adjacent structure from drill whip, and to make it possible to guide the drill by hand). Hold the drill guard as near to the drill point as possible.
Taper shank drills Tapered shank drills have a taper called the Morse taper. The size of taper incorporated on any particular drill depends on the drill diameter. At the end of the taper shank of a drill is a tongue, called the tang, and when the taper shank is fitted into the socket or machine spindle this tang engages in a slot. If the taper itself is in good condition, the frictional grip between this and the surface of the taper hole should be almost, if not entirely, sufficient to drive the drill, but if the taper becomes damaged, more load will be thrown on the tang in driving the drill, and if the drill seizes in the hole the tang may be twisted off. For this reason, every consideration to the care of taper shanks should be given in use, and they should always be extracted with the proper taper drift.
Jobbers Drills The jobbers drill is the most often-used twist drill in sheet metal work. It is a pointed tool that is rotated to cut holes in material. It is made of a cylindrical hardened steel bar having spiral flutes (grooves) running the length of the body and a conical point with cutting edges formed by the ends of the flutes. Twist drills have one to four spiral flutes. Drills with two flutes are used for most drilling; Those with three or four flutes are used principally to follow smaller drills or to enlarge holes. The principal parts of a twist drill are the shank, the body and the point. The drill shank is the end that fits into the chuck of a hand or power drill. The straight shank is generally used in hand, breast and portable electric drills.
DRILL TYPES
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Figure 44
Drill Types
Taper Shank Drill
Extension Drill
Jobber Drill
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Machine Spindle The number of the Morse taper hole in a machine spindle will depend on the size of the machine, varying from No.1 in small machines to No.4 or 5 in large ones. When a drill has to be accommodated in a spindle with a larger taper than its shank, taper sockets must be used. These should also be cared for, because if they become damaged, the drill fitted into them will no longer run true.
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Figure 45
DRIFT
Machine Spindle
BLOW
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Tang on Drill
Machine Spindle
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Grinding Drill Point Angles In order to perform correctly, the drill must be ground or sharpened properly. For general--purpose work, the drill point should be sharpened to a cone (or included) angle of 1180 (lip angle 590). This point will work satisfactorily for most drilling jobs. For very hard or tough metals, a greater angle at the point is often used. The point angle may be as great as 1400 (lip angle 700) in this case. For soft metals or fibre, the cutting angle may be reduced to 400. Plastic materials are usually drilled most satisfactorily with a cutting angle of about 300 (included angle 600) for shallow holes and with an angle of up to 700 for very deep holes. The cutting edge is ground off to produce a zero--rake angle for soft plastics such as plexiglass. For drilling stainless steels or titanium, the drill--point angle should be about 1400. For standard aluminium alloys, a drill--point angle of 1350 is very satisfactory. The point is ground with a lip relief angle ranging from about 12--15 degrees for drills used in normal hard materials. For very soft materials, this angle is usually increased to somewhere around 18--20 degrees. In grinding the drill point, it is important to see that the desired point angle and the proper lip--clearance angle are obtained. Further, it is essential that the lengths of the lips be made equal. Where they are unequal, the drilled hole will be oversize and possible out-of-round. If the cutting lips are ground with different cutting angles, the drill will bind on one side and may break. Otherwise, it will produce an oversize hole.
Introduction Do not use blunt drills or attempt to sharpen them. Using blunt drills wastes time and makes poor holes. Return blunt drills to the tool shop. The drills will be sent for resharpening. Only machine grinding is sufficiently accurate to produce sharpened drills that will cut holes to the correct size. A hand--sharpened drill usually has the point off--centre and will cut oversize holes.
GENERAL
DRILL GRINDING
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Figure 46
Grinding Drill Point Angles
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5. Check the results of grinding with a gauge to determine whether or not the lips are the same length and at a 59o angle.
4. Slowly place the cutting edge of the drill against the grinding wheel. Gradually lower the shank of the drill as you twist the drill in a clockwise direction. Maintain pressure against the grinding surface only until you reach the heel of the drill.
3. Place the hand on the tool rest with the centre line of the drill making a 59o angle with the cutting face of the grinding wheel. Lower the shank end of the drill slightly.
2. Hold the drill between the thumb and index finger of the right or left hand. Grasp the body of the drill near the shank with the other hand.
Drill Grinding Sequence 1. Adjust the grinder tool rest to a convenient height for resting the back of the hand whilst grinding.
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Figure 47
Drill Grinding Sequence
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2. Lips at different angles - Hole will be enlarged, rough hole surface.
Grinding Problems 1. Lips of different lengths - drill moves off starting position.
Point Thinning The metal at the centre of a drill (the web) tapers and gets thicker towards the shank. This causes the centre of a drill point to get thicker as its length is reduced by grinding. To prevent this thick edge from reducing the efficiency of the drill it should be ground thinner. The point thinning of a drill will usually keep the drill in a proper position when starting the hole.
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Figure 48
Grinding Problems
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Lips at Different Angles
Lips of Different Lengths
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-- When drilling, safety glasses, goggles or face shields must be used to protect the eyes. -- Remove the chuck key before starting the drill motor. Serious injury may otherwise result. -- When drilling through structure, give warning to anyone who may be on the opposite side. -- Use drill stops. They will protect aircraft skin material and understructure, as well as personnel. -- Use extreme care when drilling with extended drills. Always use extension drill guards. -- Limit drill speed to a maximum of 6000 RPM for all drills longer than three inches. -- Use only a sharp drill with the correct point angle. -- Never use a drill that is bent. -- Select a drill motor suited to job requirement: size, speed, range and configuration. -- Use the shortest drill practicable. -- If you drill magnesium or titanium alloys, ensure that there is a fire extinguisher next to you. -- Prevent your hair becoming entangled with the spindle of the boring machine.
General The following safety precautions are very important. Study them carefully.
DRILLING SAFETY PRECAUTIONS
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Pillar Drill A pillar drill is a bench--mounted or floor-mounted machine designed to rotate a drill bit and press the sharpened point of the bit against metal in order to drill a hole. The pillar drill is driven by an electric motor through a speed--changing mechanism; either a belt transmission or a gear transmission. The belt transmission consists of two stacks of V--belt pulleys which vary progressively in size from 2 to 6 in (50.8 to 101.6 cm). The pulleys are arranged so that one set decreases in size as the belt is moved up the stack and the other decreases as the belt is moved down the stack. Thus, as the belt is moved up or down the pulleys, the ratio of the motor speed to the spindle speed is changed. This is an important feature because the speed of rotation of the drill bit should vary in accordance with the type of material being drilled and the size of the hole being drilled. The pillar drill spindle is either fitted with a standard chuck or provision is made for the insertion of drill bits with tapered shanks. Many pillar drills are arranged so that a drill chuck with a tapered shank can be installed when the machine is driving small drills and, when large drills are used, the chuck can be removed and a drill with a tapered shank inserted directly into the hole in the spindle. When used correctly, the pillar drill makes it possible to do precision drill work. There should be no play in the spindle, spindle bearing or chuck and all should be in perfect alignment. The drill point should be properly sharpened and should not wobble when the machine is turned on. The work being drilled must be securely clamped to the pillar drill table so it cannot move during the operation. The operator of a pillar drill should make certain that the machine speed is adjusted correctly for the work being performed, that the drill point has the angle most suitable for the machine and that the correct drilling pressure is applied with the feed lever.
STATIONARY DRILL MACHINE
TYPES OF DRILL MACHINES
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Figure 49
Stationary Drill Machine
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9. Stop motor and remove drill and work.
8. Material will have been cut away by the drill and a hole produced.
7. Curling chips (swarf) are formed.
6. Press down drill using the feed lever. Use the recommended feed range.
5. Start pillar drill motor.
4. Wear safety glasses, goggles or face shield.
3. Clamp the work on the pillar drill table.
2. Select the correct drill and install it in the chuck.
1. Select the correct speed and adjust it on the control panel.
Pillar Drill Work Sequence
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Figure 50
Pillar Drill Work Sequence
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Angle Drill Motors Angle drill motors or power vanes are designed to be operated in tight or under limited--access places. Three head angles - 30o, 45o, and 90o - are available.
Common Drill Motors The pistol-grip or straight drill are the most often-used drill motors. These tools are ordered by drill size capacity and speed.
General The most commonly-used drill motor for drilling aircraft sheet metal is the pneumatic or air drill. The main advantage of an air drill over an electric drill is safety. Sparking in the motor of an electric drill can ignite fuel or oil vapour. It is also far less hazardous to have air hoses in the crowded aircraft structure where many sheet metal repairs are made than to have electrical cables. Another advantage is the control offered by air drills. By varying trigger pressure we can make them run slow, intermediate or high speed and there is always adequate torque. Drill motors are equipped with quick-change chucks or keyed chucks.
HAND-HELD DRILL MOTORS
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Common Drill Motors
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Figure 51
Angle Drill Motors
Hand-Held Drill Motors
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Flexible Snake Drill The flexible snake drill is used only in limited--access areas where an angle drill motor cannot be held perpendicular to the surface. The drill motor should be held in one hand, the snake drill steadied with the other.
Flat Offset Drilling Head Another tool designed for use in close quarters is the flat offset drilling head or „pork chop”. This tool uses threaded shank drills up to 1/4 inch diameter. The pork chop is ordered by spindle direction (up or down) motor speed and offset dimension.
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Flat Offset Drilling Head
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Figure 52
Flexible Snake Drill
Special Hand Held Drill Motors
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Hand Drill Handling Position for vertical drilling One hand is used for rotating the operating handle and the other for pressing the drill down. Position for horizontal drilling One hand is used for rotating the operating handle, the other holds the handle and pressure is exerted with the chest.
General The hand drill is a simple device designed to hold a drill and enable the operator to rotate the bit at a comparatively high speed. The hand drill provides a convenient means for drilling small holes, countersinking or deburring. The hand drill consists of a chuck, a handle, an operating handle, a rest and a transmission drive.
HAND DRILL
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Figure 53
Hand Drill
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Handling Precautions Do not tighten the chuck by holding it in your hands with the motor running. This practice can cause injury and can also damage the chuck or the drill. Do not start the motor with the key in the chuck; the key can cause injury. Ideally, disconnect power or air supply whilst working with the chuck.
Using the Keyed Chuck The chuck of a drill machine is a tool which tightens the drill, countersinking bit, reamer, etc. In using the keyed chuck, be sure to use the correct-size chuck key. The key should mesh easily but firmly with the teeth of the chuck. In use, hold the key securely in mesh with the chuck teeth, to prevent it slipping. Turn the key counter--clockwise until the tool slips easily into the chuck jaws. Turn the key clockwise and tighten the tool securely in the jaws, using at least two different keyholes and make sure that the tool shank is gripped uniformly in all three jaws. Check the tightness of the tool. If necessary, tighten further, using the third keyhole.
THE CHUCK OF A DRILL MACHINE
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Figure 54
Keyed Chuck
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1. Hold the drill motor as shown. Notice that the thumb and forefinger of one hand are used to steady the motor. This method can be used only with a short drill. Short drills are always preferred. 2. Put the drill point on the spot to be drilled. 3. Keep the drill perpendicular to the surface being drilled. If necessary use a drill guide. 4. When drilling thick material (two or three times drill diameter or more), withdraw the drill from the hole periodically to prevent chips from packing in the drill flutes. Tightly-packed chips can cause an oversized, scarred hole. 5. Use just enough pressure to allow the drill to cut its way through the metal. Never force the drill; this can cause drill breakage, separation of parts or oversize or out--of--round holes. 6. Ease the pressure just as the drill point breaks through the material. Drill through material no more than 1/4 inch thick. 7. Use a drill-stop to prevent the drill from going through the part further than necessary (adjust the stop). If a drill-stop is not used, the part may be damaged by the drill chuck, and the underlying structure may be damaged by the drill point. 8. Keep the drill motor running while withdrawing the drill from the hole.
Using the Drill
GENERAL
DRILLING WORK SEQUENCE
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✘
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Figure 55
Using The Drill
Pressure on centre-line of drill
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Set drill-stop to material thickness + .10 inch
Set screw
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Drill-stop
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Special Deburring Tool This tool is designed to deburr holes on the exit side which you could not reach with standard deburring tools, due to limited access. This tool is chucked in a drill motor for rapid work. The retractable blade is held in place by spring pressure. To use, push the tool through the hole and remove burrs from the exit side. Then draw the tool back through the hole and remove burrs from the entry side. This deburring tool comes in common hole sizes from 5/32 to 3/8 inch
General When holes are drilled through two sheets of material, small burrs are formed around the edges of the holes and chips can be pushed between the two sheets. It is therefore essential to remove the burrs and chips. Removal of burrs from drilled holes may be accomplished with a manufactured deburring tool, a countersinking tool (using a very light cut) or a large drill which will clear the edges of a drilled hole. Care must be taken to remove only the rough edges and chips from the hole. When two or more sheets are drilled at the same time, it is necessary to remove chips from between the sheets. The right-hand picture shows the results of leaving material between drilled sheets.
DEBURRING
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Figure 56
Deburring
Special Deburring Tool
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Indication
Aug 2004
Hole oversize
Hole wall rough
Drill will not feed into material
Drill splits up its centre
Drill breaks
Cracks in drill cutting edges Drill point improperly ground. Excessive feed rate. Drill blunt. Flutes clogged with swarf.
Drill point improperly ground/blunt. Insufficient or incorrect lubricant. Excessive feed rate. Material not rigid. 1. Unequal angle and/or length of cutting edges. 2. Loose spindle.
1. 2. 3. 4.
1. Drill blunt. 2. Insufficient drill cutting edge clearance. 3. Drill too large (i. e. pilot hole required).
1. Insufficient drill cutting edge clearance. 2. Excessive feed rate.
1. 2. 3. 4.
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1. Drill overheated or cooled too quickly whilst sharpening or drilling.
1. Excessive feed rate. 2. Excessive drill cutting edge clearance.
Probable Cause 1. Excessive cutting speed. 2. Hard spots in the material. 3. Flutes clogged with swarf.
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Parts of the cutting edges break off
Outer corners of drill break off
COMMON DRILLING PROBLEMS
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Drilling Hints 1. For soft metals use a drill with a quick twist to its flutes, and vice versa for hard metals. 2. Cut with soluble oil for steel and malleable iron, kerosene or turpentine for very hard steel. Cast--iron or brass should be drilled dry, or with a jet of compressed air. 3. If the corners wear away rapidly, the cutting speed is too high. 4. If cutting edges chip, reduce the feed or grind with less clearance. 5. If the drill will not start drilling there is no clearance on lips. 6. Examine relative sizes of turnings produced from each flute. They should be approximately the same but, if not, the drill is incorrectly ground with one lip doing more cutting than the other. 7. Drill breakage may be caused by the point being incorrectly ground; feed too great; not easing drill at ”break through”; binding in hole due to lands being worn away; drill choked in a long hole. 8. The blueing of a high--speed steel drill is not detrimental but it is fatal to a carbon steel drill. 9. A hard spot encountered may be removed by reducing speed and using suitable cutting compound or fluid. 10.For holes larger than 3.2mm, it is necessary to initially drill a pilot hole and enlarge it to the required hole size.
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Clamps and Dogs The tables of most pillar drills are provided with either T-slots to accommodate bolt heads or long slots running through to enable bolts and clamps/dogs to be used.
Vice Most work will be secured by using a vice. The main use of the vice is to hold the work during drilling, reaming etc. in the correct position. Care should be taken to ensure that when the drill passes through the work it does not drill into the bottom of the vice.
Pillar Drill Clamping To secure work when using the pillar drill a vice, clamps and dogs are often used.
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General Unless work is so large and heavy that there is no danger of its moving or being rotated with the drill, it should always be clamped or held by some method. The necessity for clamping cannot be understated because unclamped or insecurely clamped work is not only a cause of inaccurate work and broken drills, but also a danger to the operator. The chief danger in drilling occurs just as the drill point breaks through at the underside of the part being drilled. Whilst the point is being resisted by solid metal, the feeding pressure causes some spring-back to take place in the machine and the work, putting them into a similar condition to a strong spring which is compressed slightly under a load. As soon as the drill point breaks through, most of the resistance against it suddenly vanishes and the stress in the machine releases itself by imparting a sudden downward push onto the drill, just as a sudden relieving of the load from a spring would allow the end of it to jump up. The sudden downward push on the drill generally causes one or both of the lips to dig in, often with disastrous results. When feeding the drill by hand, pressure should be eased off when the point is felt to be breaking through, and for this reason small drills should always be fed by hand. Special care is necessary when drilling thin plate, as the drill point often breaks through before the drill has cut its full diameter.
WORK CLAMPING
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Figure 57
Pillar Drill Clamping
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Hand Drill Clamping When using a hand drill motor, the work to be drilled must be properly secured so it cannot move. It should never be held by hand because, in the event of a broken drill, the broken end may pierce the hand or a finger, causing a painful injury. Angle vices, pin vices, hand vices etc. are to be used to hold the work to be drilled in position.
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Figure 58
Hand Drill Clamping
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THE TOTAL AMOUNT THAT THE STOP-DRILL HOLE MAY BE ENLARGED MUST BE DETERMINED FOR EACH SPECIFIC CASE DEPENDENT UPON THE LOAD PATTERN AND STRESS LEVEL IN THAT AREA. 3. Install a 2017--T3 flush plug rivet in the stop-drilled hole, if required.
NOTE:
Stop drilling of cracks (Ref. SRM (Structural Repair Manual): hole preparation and stop drilling of cracks) Propagation of a crack may be stopped by drilling a hole at the end of the crack as follows: 1. Drill or counterbore a 0.25--inch diameter crack stop-hole through the structure at the end of a crack. Locate each stop-hole so that the centre of the hole is 0.10 inch beyond the visible end of the crack. 2. Carry out an Eddy Current Method inspection of each stop-drilled hole to confirm that there is no further cracking extending beyond the hole. S If the crack has not continued through the hole, enlarge the hole to 0.312--inch diameter to ensure the removal of fatigue-damaged material. S If the crack has continued through the hole, enlarge the hole by additional l/16-inch diameter increments until the crack indication is removed. Enlarge the hole an additional 1/16 inch in diameter to remove any fatigue damaged material.
ADDITIONAL TOOLS FOR DRILLING
DRILLING AIDS
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Drill guide The hand-held drill guide keeps the drill 90o to the skin surfaces. The guide assembly consists of a clear plastic housing and special screw in type hardened steel bushing. The bushing can be interchanged.
Drill stop The drill stop regulates the hole depth, cushions the break through, eliminates surfaces marks and reduces drill breakage. The drill stop locks onto the drill with a set screw.
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Figure 59
Drill Stop and Drill Guide
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2. Align the pilot with the pilot hole, pilot-pin the hole drilled in the first operation and then drill the second hole.
Drill Jig Handling 1. Align the pilot with the pilot hole when drilling the first hole.
Nut Plate Drill Jig The nut plate drill jig is designed for accurate drilling of rivet holes for nut plates (sometimes called ’anchor-nuts’). It is manufactured with a flexible handle to provide hand clearance when the jig is in use. There are a lot of different drill jigs available.
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Figure 60
Nut Plate Drill Jig
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Hole Finder When replacing an old skin with a new one, if there are no pilot holes drilled in the new skin it is quite difficult to precisely locate the holes in the structure. For this procedure, a hole finder (sometimes called a ’back-marker’) may be used. The finder resembles a clamp that slips over the new skin, and on its underside is a pin that exactly fits through the hole in the structure. A hole in the top side guides the drill in making a hole in the new skin that will align with the one in the structure.
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Figure 61
Hole Finder
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Drill Gauge The size of a drill is stamped on its shank. If the size cannot be read, it can be determined by using a drill gauge. Drill gauges are available for all three series of drill sizes; fractional, letter and number. Fractional drills are furnished in sizes from 1/16 to 1 inch in diameter, graduated in sixty--fourths of an inch. Letter drills range in size from A (the smallest) to Z (the largest). Number drills range from I (the largest) to 80 (the smallest). To gauge a drill, insert the point into a hole in the drill gauge (remember the shank is fractionally smaller than the point). If the drill slips easily into the hole, insert it into the next smaller hole. When the correct size has been determined, the drill will rub lightly in the hole.
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Figure 62
Drill Gauge
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Remaining Boelube residue must be removed within 48 hours after use.
-- compatible with most lubricant application systems
-- removed by solvent wiping or washing with warm water and mild detergent
-- excellent lubricating properties under extreme pressure
-- non--toxic, non--polluting and non-irritating under normal conditions
Boelube lubricants have the following characteristics:
Boelube Boelube is used as an agent for drilling aluminium, magnesium and steel, as well as titanium. Boelube consists of cetyl alcohol, a non--toxic lubricant from the fatty alcohol chemical family. It is suitable for many production operations and is manufactured in solid, paste, and liquid forms. It is approved for use with aluminium, steel or titanium materials. It is also sealant- and paint-compatible, and is non-corrosive. Disassembly for cleaning is not required in sealant or paint areas.
General Drilling agents are recommended (unless prohibited by the engineering drawing) to improve tool life, hole tolerance and hole finish. Recommended cutting agents for drilling, reaming, and countersinking are shown in the following table. Cutting agents are mandatory only when so specified.
DRILL AGENTS
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④
Directly to cutting tool
BOELUBE (Countersinking)
Directly to cutting tool Directly to cutting tool Mist
Flood, mist or through oil hole drill or reamer ② Directly to cutting tool
Mineral oils BOELUBE (countersinking) Freon TB-1 Water soluble coolants or BOELUBE BOELUBE (Countersinking)
①
Flood, mist or through oil hole drill or reamer ②
Water soluble coolants or BOELUBE
③
Flood, mist or through oil hole drill or reamer or directly to the cutting tool ②
Water Soluble Coolants or BOELUBE
①
Mist
Application
Freon TB-1
Cutting Agent
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① Freon and TB-1 must be applied as a mist. Several systems for applying TB-1 are available and are generally supplied by the tool rooms or to the shop as shop equipment. ② ST1219C-11T mist coolant tank was designed for water soluble coolants. Do not use Freon TB-1. ③ Special systems have been designed for application. ④ Refer to BAC 5440 for lubricants and application when it is specified on the engineering drawing.
Titanium
Steel (includes stainless steels)
Aluminium and Magnesium
Material
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General Twist drills used in aircraft sheet metal are usually of the number drill sizes between one and sixty. However, for larger-sized holes either fraction drills or letter drills may be used. The diagram opposite shows a twist--drill size chart that lists sizes from No. 80, the smallest normally in use, up to 5/16 inch. There are, of course, drill sizes smaller and larger than those listed, but they fall outside of the general use of the aircraft mechanic. You will notice that the smallest drills have the largest numbers; for example, a No. 80 drill is much smaller than the No. 1 drill. In addition to the number drills, there are letter drills from A to Z, with A being the smallest. The fraction drills are interspersed among the number and letter drills, and only at one point do we find a fraction and a number or letter drill of the same size; both the 1/4-inch drill and the E drill are 0.250 inch.
DRILLING SIZES
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Figure 63
Drill Size Chart
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Table IV--5 Material / RPM - Drilling composite with metal (graphite or kevlar epoxy and aluminium stack, and graphite or kevlar and titanium stack)
Table IV--4 Material / RPM - Drilling nonferrous metals (fibreglass laminates, nylon Teflon, graphite, epoxy, kevlar epoxy)
Table IV--3 Material / RPM - Drilling nonferrous metals (aluminium alloys, magnesium)
Table IV--2 Material / RPM - Drilling high Temperature alloys (Inconel, titanium)
Material / RPM tables Table IV--1 Material / RPM - Drilling ferrous metals
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Introduction Drill speeds are an important factor in getting good results. Drill speed determines the rate at which the outer cutting edge of the drill is moving across the material being out. The correct speed for aluminium alloy will not produce the best results with stainless steel or titanium. When harder materials are drilled, slower speeds are required. The following drill speed tables are recommended for drilling. Material / revolutions per minute (RPM) values and speeds and feeds for most materials commonly used are given. These speeds and feeds are a guide for selecting the correct portable and stationary drilling units to improve tool life, hole tolerance, and hole finish. In some portable drilling applications, speeds and feeds may have to be reduced to be compatible with motor power and other limitations. However, the speeds and feeds shown in the tables should never be exceeded. Despite all these facts and figures, though, for practical purposes use the correctly-ground drill and appropriate lubricant, start drilling slowly and increase the revolutions until swarf starts to appear. Then you know you are using the correct drill speed.
GENERAL
DRILL SPEEDS
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Figure 64
RPM Table IV - 1
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RPM Table IV - 1 (Continued)
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RPM Table IV - 1 (Continued)
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RPM Table IV - 1 (Continued)
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RPM Table IV - 1 (Continued)
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RPM Table IV - 1 (Continued)
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Table IV - 2
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Table IV - 2 (Continued)
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Table IV - 3
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Table IV - 4
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Table IV - 4 (Continued)
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Table IV - 4 (Continued)
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Table IV - 5
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Table IV - 5 (Continued)
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REAMING
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Interference Fit In this assembly there is no space between the parts. The shaft is always larger than the part it fits into. This means that force is required to assemble the parts.
Clearance Fit In this assembly there is a space between the two parts. The shaft is always smaller than the part it fits into.
The ISO system of limits and fits gives a range of sizes to which parts should be made if the type of fit is known. The following list gives you examples of the types of fit in use: S Clearance fit S Interference fit S Transition fit
THE ISO SYSTEM OF LIMITS AND FITS
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0.02 = Tolerance
24.99 -
25.01
Page: 163
If you subtract the lower limit from the upper limit the result is known as the tolerance.
24.99 -- Lower limit
25.0I -- Upper limit
Tolerances The type of fit between two assembled parts depends on the size to which each part is made. Since no size can be exact, then each part must be made within two sizes. The two sizes within which a part must be made are called limits. If the basic size (also known as the nominal size) of the part is 25mm then the limits could be given as
Transition Fit This is a range of fits which can be either clearance or interference. The shaft can be larger or smaller than the part it fits into.
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General In precision manufacture it is not possible to make an engineering component to an exact size. Gauge blocks are considered to be very accurate standards of length, but even these are not exact. If a component cannot be made to an exact size then the amount by which it can be in error (known as the deviation from the exact size) must be known and included with the dimension. If moving parts in machines are to function properly, then the relationship between the size of one part and the size of the part which fits into it is of extreme importance. When. for example. manufacturing a shaft which has to run freely in a bearing. there must be enough space for a film of oil between the two in order to prevent wear. The maximum and minimum permanent sizes of a component are known as limits. The difference between the maximum and minimum sizes (limits) is called tolerance. There are a number of limits and fits systems in use which give the largest and smallest size of a part for any required type of fit.
LIMITS AND FITS
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CLEARANCE FIT
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Figure 78
Basic Types Of Fit
Can be clearance or interference
TRANSITION FIT
CLEARANCE (space between hole and shaft)
A force is required to push the shaft through the hole
NO CLEARANCE
INTERFERENCE FIT
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The Shaft Basis System of Fits In this system the shaft is the fixed size and the hole sizes are varied. This system is sometimes used when a variety of components. e.g. bearings. couplings. gears etc. are all to fit the same shaft.
The Hole Basis System of Fits This is the preferred system. The range of fits is obtained by manufacturing the hole to a fixed size and the shaft size is varied. This system is preferred because reamers, for example. are made in a range of standard sizes. (It would be impossible to make a range of reamers to cover all types of fit.)
Systems of Fits There are two systems of fits in use: S Hole basis system S Shaft basis system
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Figure 79
ISO Fits (Hole Basis) - British Standard 4500
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Basics Reaming is a process in which a fluted tool, called a reamer, is used to enlarge a drilled hole. Reaming is a finishing operation that provides closer control of hole sizes and better finish than drilling alone. In normal practice, a hole that is to be reamed is drilled 1/32 inch under the finished hole size. Reamer pilots are sized to suit the drilled holes. Before using a reamer on a production part, try it out on scrap material of the same alloy and thickness in a drilled hole of the same size as the one to be reamed. Verify that the reamer will cut to the required tolerance or continue testing until the right combination of reamer size, speed and feed is found. A reamer will generally produce a hole that is from 0.0001 to 0.002 inch larger in diameter than the exact size of the reamer. Reamer are made of either carbon tool steel or high--speed steel. The cutting blades of a high--speed steel reamer lose their original keenness sooner than those of a carbon steel reamer. However, after the first super-keenness is gone, they are still serviceable. The high--speed reamer usually lasts much longer than the carbon steel type. Reamer blades are hardened to the point of being brittle and must be handled carefully to avoid chipping them. When reaming a hole, rotate the reamer in the cutting direction only. Turn the reamer steadily and evenly to prevent chattering, or marking and scoring of the hole walls. Reamers are available in any standard size. The straight--fluted reamer is less expensive than the spiral--fluted reamer, but the spiral type has less tendency to chatter. Both types are tapered for a short distance towards the end to aid in starting.
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-- Removing reamer from hole.
-- Amount and type of lubrication.
-- Sharpness of reamer.
-- Rate of feed (pressure).
-- Speed of reamer.
-- Amount of material being removed by the reamer.
-- Hardness of material being reamed.
Page: 167
Bottoming reamers have no taper and are used to complete the reaming of blind holes. Many factors affect the finished size of a reamed hole. The following are the most common: -- Pilot hole diameter.
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Introduction Holes must be of high quality. Finishing operations such as reaming improve the quality of the hole. Under certain flight conditions, the maximum design strength of every fastener is required. Proper hole fill is essential in attaining maximum design strength. When a fastener does not fill the hole, it is the weak link in a chain of several fasteners. Care and good workmanship are essential in reaming high quality holes. Surface defects of holes are given in the SRM Chapter 51 ”Surface Defect Criteria for Fastener Holes in Metal“.
REAMING GENERAL
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Figure 80
Table Of Defect Criteria (ATA-Chapter 51-- 40-- 05)
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Right--hand twist affects the direction of the removal of chips like a normal twist drill. The Left--hand twist moves the chips into the advance direction. The chips cannot have an adverse effect on the reamed part of the holes drilling. Therefore left--hand twist--fluted reamers are only suitable for transmission drills. They have the advantage that they do not tend to pull themselves into the hole. When reaming grooved holes, it is better to use spiral--fluted reamers.
Left--hand twist -- Right--hand twist (For the use of Right--hand cutting tools)
Chucking grooves Chucking grooves are the spaces between the single teeth; all chips are collected and transported in these spaces. The course of the chucking grooves affect the direction of the removal of chips. There are straight--fluted and spiral--fluted reamers. Straight--fluted reamers have no precise affect on the direction of the removal of chips. They have a low abrasion and are the most used type. Spiral--fluted reamers, on the other hand, lead the removed chips in a definite direction.
Shaft Shafts of reamers can take different shapes and forms. There is never a characteristic shape for either a hand-- or a machine--reamer. The type of driving mechanism determines the shape of the shaft. Hand reamers mostly have a cylindrical shaft with a square end (for a tap wrench). Shafts of machine--reamers are mostly designed as Morse tapers.
REAMER DESCRIPTION
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Square
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Shank
Reamer
Flutes (body)
Figure 81
Neck
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Straight flutes
Spiral flutes
Chamfer (straight taper)
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Spacing Vibration of the tool or work whilst cutting often leads to undesirable chatter marks. Modern reamers are made with an uneven spacing; in that way the effect of periodical vibration is reduced. Remove the reamer from a hole by rotating it in the cutting direction (working direction). Otherwise, due to the wedge effect of the chips at positions A and B, the hole surface and/or the cutting edges will be damaged.
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Figure 82
Space Of Cutting Edges
Correct direction of rotation of reamers (working direction)
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Spacing and diametral pitch are designed in such a way that two cutting edges are facing one another (measurability)
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Machine Reamer The machine reamer is designed with a large cutting angle, short major cutting edges (short first cut) and short overall cutting edges. Due to the short first cut the machine reamer, in principle, can only be used if the work piece and the reamer have no axial play during the reaming process. So you cannot use a hand drill. The advantages of a machine reamer are a much higher cutting capacity and the possibility of reaming dead centre holes.
General There are two basic types of reamers; the hand-- and the machine--reamer.
TYPES OF REAMERS
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Shank length
Figure 83
Chamfer relief angle
Chamfer angle
Margin
Land width
Machine Reamer
Actual size
Chamfer relief
Helix angle
Cutter sweep
Overall length
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Chamfer length
Straight shank
Taper shank
Shank length
Tang
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Radial rake angle
Helical flutes RH helix shown
Chamfer angle
Flute length
Body
Actual size
Chamfer length
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Hand Reamer The hand--reamer is designed with a small cutting angle, large major cutting edges (large first cut) and large overall cutting edges. The hand--reamer will be guided into the hole through the long first cut and the long major cutting edges.
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Land Width
Square
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Shank
Taper
Starting
Land
Hand Reamer
Bevel
Actual size
Cutting edge
Margin
Flutes (body)
Figure 84
Neck
Core diameter
Flute
Cutter face
Heel
Relief angle
Relieved land
Spiral flutes
Straight flutes
Chamfer (starting taper)
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Pilot Chuck Reamer The pilot chuck reamer is the most commonly used reamer which gives accurate lead into a drilled hole and a superior finish.
Pilot Reamer The pilot reamer is guided into the hole through a bushing.
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Figure 85
Pilot and Pilot Chuck Reamer
Pilot Chuck Reamer
Pilot Reamer
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Taper Reamer This reamer is used to finish a taper hole (for example for a taper shank bolt) accurately and with a smooth finish. Because of the long cutting edges, taper reamers are somewhat difficult to operate.
Expansion Hand Reamer This reamer is used when the hole must be cut a few thousandth of an inch over nominal size for fitting purposes. Slots are cut into the hollow centre of the tool and the centre opening is machined on a slight taper. The reamer is expanded by tightening a taper screw into this opening. The amount of expansion is limited and the reamer could be damaged if overexpanded. It is not recommended that the expansion reamer be used in place of a solid reamer because of the danger of producing oversize holes.
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Figure 86
Expansion Hand Reamer and Taper Reamer
Taper Reamer
Expansion Hand Reamer
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Adjustable Hand--Reamer This reamer is threaded its entire length and fitted with tapered slots to receive the adjustable blades. The blades are tapered along one edge to correspond with the taper slots in the reamer body so that, when they are in position, the cutting edges of the blade are parallel. The diameter of the reamer is set by loosening one adjusting nut and tightening the other. The blade can be moved in either direction. This type of reamer is manufactured in sizes ranging from 3/8-1/2 inch and each reamer has sufficient adjustment to increase the diameter to the size of the next larger reamer.
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CUTTER
Figure 87
Adjustable Hand Reamer
Adjustable Hand Reamer
LARGER
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TAPER
SMALLER
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Reaming composites and composites with metal
Table V--5
Aug 2004
Reaming titanium or aluminium stackup
Table V--4
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Reaming titanium alloys
Table V--2
Reaming speeds The reaming speed is the speed of the chip removal. The recommended material / RPM values (speeds and feeds) for reaming are shown in the following tables: Table V--1 Reaming aluminium alloys
REAMING SPEED AND AGENTS
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Figure 88
Table V - 1
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Figure 89
Table V - 1 (Continued)
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Figure 90
Table V - 1 (Continued)
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Figure 91
Table V - 2
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Table V - 2 (Continued)
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Table V - 2 (Continued)
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Table V- 4
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Table V - 5
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Table V - 5 (Continued)
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Reaming Agent To ream a hole to a high degree of surface finish, a cutting agent is needed. A good agent will cool the work and tool, and will also act as a lubricant between the chip and the tool to reduce friction and heat build--up. The following cutting agents given in Table VII--l are recommended (unless prohibited by the engineering drawing) to improve tool life, hole tolerance and hole finish.
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④
Directly to cutting tool
BOELUBE (Countersinking)
Directly to cutting tool Directly to cutting tool Mist
Flood, mist or through oil hole drill or reamer ② Directly to cutting tool
Mineral oils BOELUBE (countersinking) Freon TB-1 Water soluble coolants or BOELUBE BOELUBE (Countersinking)
①
Flood, mist or through oil hole drill or reamer ②
Water soluble coolants or BOELUBE
③
Flood, mist or through oil hole drill or reamer or directly to the cutting tool ②
Water Soluble Coolants or BOELUBE
①
Mist
Application
Freon TB-1
Cutting Agent
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① Freon and TB-1 must be applied as a mist. Several systems for applying TB-1 are available and are generally supplied by the tool rooms or to the shop as shop equipment. ② ST1219C-11T mist coolant tank was designed for water soluble coolants. Do not use Freon TB-1. ③ Special systems have been designed for application. ④ Refer to BAC 5440 for lubricants and application when it is specified on the engineering drawing.
Titanium
Steel (includes stainless steels)
Aluminium and Magnesium
Material
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If you take a reamer or a reamer set out of the toolshop, check out given dimensions marked on the shank with the given hole sizes in the SRM.
Reamers should be stored so that they do not get in contact with another reamer to avoid burrs on the tools.
Check the reamer if it gradually starts cutting larger holes; it may be caused by built--up edges on the reamer cutting surfaces. Some aluminium alloys and mild steel are affected by these built--up edges.
Oversize holes can be caused by inadequate work support, worn guide bushings, worn or loose spindle bearings or a bent reamer shank.
Chatter corrections may be made by reducing the speed, increasing the feed or using a reamer with a pilot.
When removing the reamer from the hole rotate it by hand in the direction of the cut; backing up the reamer will dull it.
Stop reamer rotation as soon as the reamer’s major diameter breaks through.
General Do not try to straighten the drilled hole by applying side pressure; you will probably cut oversize.
REAMING ADVICE
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Figure 97
Reaming Advice
90˚
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BUILT-UP EDGE
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COUNTERSINKING
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IN GENERAL, ALL SHEET METAL WORK IS DONE USING 100O FASTENER HEADS.
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NOTE:
Introduction To install a countersunk fastener, it is necessary to provide a conical cut-out or depression in the surface of the skin so that the head of the fastener will be flush with the surface. This provides smooth aerodynamic surfaces on airplane structures or smooth surfaces for attaching adjoining members. The use of countersinks on riveted joints also provides weight saving by eliminating the weight of the rivet head material. The depression is made by means of a countersinking tool when the skin is sufficiently thick and by dimpling when the skin is thin. The use of a machine countersink is limited by the size of the fastener and the thickness of the skin. Generally, sheet metal should not be countersunk entirely through the sheet (See SRM - minimum sheet thickness for countersinking for fasteners), as this results in ’knife-edging’ - potential crack sources. A countersinking tool is usually provided with a straight shank for use in a hand drill, a drill motor or a bench drill. Countersinks are made with a variety of cutting angles. In sheet-metal work, countersink cutters are available for 82o, 100o and 120o fastener heads, and for special NACA rivets. Always be sure that the cutting angle you use is the correct one for the fastener to be used.
GENERAL
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Figure 98
M7 MAINTENANCE PRACTICES TOOLS
Example Table Of Sheet Thickness For Countersinking
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Standard Countersink with Pilot This type of tool looks like the standard countersink. The only difference is the pilot pin which guides the countersink into the material.
Standard Countersink / Plain Counter A standard countersink can be used in a drill motor or a hand drill, but the difficulty in cutting the depression to the correct depth makes this tool impractical when you have several holes to countersink. Standard countersinks are available with one, three or multiple cutting lips.
COUNTERSINKING TOOLS
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Countersink / Plain Counter
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Figure 99
Standard Countersink
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Countersink With Pilot
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Always be sure that the cutting angle you use is the correct one for the fastener to be used.
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NOTE:
Microstop Countersink For general purposes the microstop countersink, fitted with a removable cutter, has been proved to be the most efficient countersinking tool. This tool controls countersink depth and keeps the cutter perpendicular to the work surface. The microstop is equipped with a removable cutter and pilot. The cutter consists of a cutting head and a pilot that may be removable. Countersink cutters are available for 82o, 100o and 120o fastener heads and for special NACA rivets.
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Figure 100
LOCKING RING
CUTTER
PILOT
SKIRT (BROKEN VIEW)
Typical Microstop Countersink
BARREL
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ENSURE THE CUTTER IS SEATED IN THE COUNTERSINK SHAFT BEFORE USING THE STOP COUNTERSINK, OTHERWISE INCORRECT DEPTH OF COUNTERSINK WILL RESULT.
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NOTE:
MAKE SURE THAT THE LOCKING SPLINES INTERMESH; ONLY THEN IS THE ADJUSTMENT SECURELY LOCKED. IN GENERAL, ADJUSTMENT OF THE MICROSTOP WILL BE MADE ON SCRAP MATERIAL. The stop countersink may be adjusted or set up on the part to be countersunk, providing the following precautions are taken: 1. Be sure the adjustable foot piece is extended far enough to ensure that the cut will not be too deep. 2. Gradually increase the depth adjustment until the depth and diameter of the hole are the same as the size of the fastener head. 3. If at all doubtful of the accuracy of the adjustment, try the countersink on a piece of scrap material before using. The pilot pin guides the spinning cutter as it cuts into the material. The pilot pin is approximately 0.002 inch less in diameter than the fastener hole. This allows the cutter to spin without binding in the hole. Cutter-- pilots which are more than 0.002 inch smaller than the hole size will allow the cutter to wobble and result in a lop--sided countersink.
NOTE:
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WHEN COUNTERSINKING A CONCAVE OR CONVEX ITEM, THE CUTTER WILL NOT CUT TO THE SAME DEPTH AS SET UP ON A FLAT PIECE OF MATERIAL. TRY TO SET UP ON A TEST-PIECE OF THE SAME CURVATURE. Ideally a countersink tool will have a nylon face fitted to minimise damage to the workpiece. Chips will become embedded in this face during the countersinking operation. It is vital that the skirt is prevented from rotating (see diagram) to stop these chips becoming ground into the workpiece.
NOTE:
In actual practice, the proper depth of the countersink is determined by driving a test rivet in a scrap piece of metal. The depth adjustment of the microstop countersink tool is gradually increased until a countersink depth is obtained that provides the required flushness of a driven rivet. Once the correct countersink adjustment has been established in this manner, the tool can be used for countersinking on the actual job.
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Instructions For Using Microstop Countersink Tool The shaft of the microstop countersink tool rotates on a bearing inside an adjustable locking sleeve and foot piece assembly. The foot piece (or ”stop” as it is often called) screws onto the shaft bearing, enabling depth adjustments to be made. Markings, indicating depth differentials in 0.001--inch increments, surround the bevelled circumference of the locking sleeve to aid in depth adjustments. Adjustment is made by pulling the sleeve back and turning the stop to increase or decrease the cut. The sleeve is then dropped back into its original position to effect a lock.
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ADJUSTMENT OF MICROSTOP COUNTERSINK TOOL
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Figure 101
Microstop Handling
HOLDING MICROSTOP COUNTERSINK TOOL SKIRT
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COUNTERSINK CUTTER
1/2 100˚ 1/8
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Back Countersinking The back countersinking tool is used to countersink inaccessible holes. The tool consists of a pilot rod and a countersink cutter. The rod must be slightly smaller than the hole. Work sequence 1. Install the rod in a drilling motor. 2. Insert the pilot rod through the hole. 3. Attach the cutter to the rod end. 4. Start drilling motor and pull back the motor.
M7 MAINTENANCE PRACTICES TOOLS
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PILOT ROD
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COUNTERSINK CUTTER
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Figure 102
Back Countersinking
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Spotfacing Spotfacing is the method used for cutting a flat area or seat for a bolt head or nut on a contoured or uneven surface. This operation should be done in a pillar drill whenever possible, but must occasionally be done with hand--held equipment. Spotfacers have interchangeable pilots that must be slightly smaller than the fastener hole. The spotfacer diameter will be called up on the drawing. The operator should use a pilot 1/32 inch smaller than the hole.
M7 MAINTENANCE PRACTICES TOOLS
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Figure 103
Spotfacer
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General -- Because countersinking is done through skin tape or through a protective spray coating, allow for this added thickness when adjusting countersink cutter depth. -- Be sure the skirt of the countersink tool is smooth and polished; burrs or nicks on the skirt may mark the skin. -- Do not allow the skirt to rotate on the metal; this can scratch the skin. -- Be sure the locking ring is kept snug; the ring tends to work loose during use. -- Countersink depth requirements are given in the SRM (aerodynamic smoothness) for each airplane. -- Periodically check countersink depth throughout the countersinking operation to ensure that flushness requirements are being met. Countersink depth will vary depending upon the skin thickness and understructure support. -- Before using, check countersink cutter for pilot size, sharpness, angle and true running. -- Hold countersink at a 90o angle to material. -- Cut to full depth each time. -- Apply pressure directly behind countersinker. -- Ensure there is a thickness of material behind the skin being countersunk to guide the pilot to prevent chattering of cutter.
GUIDELINES FOR COUNTERSINKING
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General Cutting agents are recommended (unless prohibited by the engineering drawing) to improve tool life, hole tolerance and hole finish. Recommended cutting agents are shown below.
COUNTERSINK CUTTING AGENTS / SPEEDS
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Figure 104
Cutting Agents
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Figure 105
Cutting Guidelines
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THREAD CUTTING
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UNC UNF
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The Whitworth thread form was once a widely-used general-purpose thread. The British Association thread form is widely used for small screws in electrical fittings and scientific apparatus. It has a metric pitch.
There are two series: Unified National Coarse Unified National Fine
General There are several different thread forms. In the illustration opposite you can see some of the commonly-used threads. Observe how one thread form differs from another by comparing: S The thread angle S The shape of the crest S The shape of the bottom of the groove S The height and pitch of the thread. The ISO thread form is a modern general purpose screw thread form, developed by the International Standards Organisation for both metric and imperial Series threads. The American National and DIN metric thread forms are commonly used on aircraft. The root of an external thread is rounded. The crest may be either rounded or flat depending on the method of manufacture. The root of an internal thread is usually rounded. The crests are usually flat.
THREAD FORMS
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Figure 106
American National Thread & DIN Metric Thread
Thread Forms
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ISO Metric / Unified Imperial Series Thread
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British Association Thread
Whitworth Thread
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Screw Pitch Gauges Screw pitch gauges are used to determine the pitch of a thread quickly and exactly. S Select a screw pitch gauge of the correct thread form. S keep the leaf parallel to the thread axis. S Check that the gauge leaf fits the thread accurately. S Read the required pitch directly from the leaf that accurately matches the thread.
Unified National Threads The pitches are given as the number of threads per inch. Below 1/4-inch diameter the nominal size is given as a series of numbers from 0 to 12. Above 1/4-inch diameter the nominal size is given as fractions of an inch. For example, a 3/16 inch bolt with UNF thread has the nominal diameter number of 10 and 32 threads per inch. The designation of this screw is 10--32 UNF.
THREAD PITCH
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Screw pitch gauge
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Figure 107
Screw Pitch Gauge
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Internal
External
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The Die Dies have three or more flutes to form cutting edges on the internal threads and cavities for removal of chips. They have chamfers ground on the first few threads of the leading end of the die to facilitate easy starting.
The Stock The stock is the tool used to hold and turn a threading die when producing external threads by hand.
HAND THREADING TOOLS
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Handle
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Stock
Leading face of die
Hand Threading Tools
Cutting teeth
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Figure 108
Recess for die
Locking and adjusting screws
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Die
Leading face of die
Chamfer
Flute
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Hand Taps Hand taps have three or more flutes to form cutting faces on the external threads and channels for removal chips. Hand taps have chamfers ground on the leading threads of the tap to enable easy starting. The end of the shank is squared to allowed it to be gripped firmly in the tap wrench.
Tap Wrench Tap wrenches are tools used to hold and turn a tap when cutting internal threads by hand. Tap wrenches have adjustable jaws to grip the hand tap.
HAND TAPPING TOOLS
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Adjust jaw by turning handle
Hand Tapping Tools
Flute
Chamfer
Tap wrench grips squared part of shank
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Figure 109
Bar-type tap handle
Aug 2004
Handle
Jaws
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Hand tap
Cutting face
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Regular Hand Taps Each regular hand tap set consists of a taper, an intermediate and a bottoming tap. Each tap in a set has identical length and thread measurements and only the tapered lead is different. S Always use the taper tap to start thread. S Use the intermediate tap to follow the taper tap. S Use the bottoming tap to complete the thread.
TYPE OF TAPS
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Taper tap
Start with taper tap
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Figure 110
Types of Taps
Intermediate tap
Use intermediate tap after taper
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Bottoming tap
Page: 228
Bottoming completes thread
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Size and Condition Holes of the correct size and condition are essential for successful tapping. Theoretically, a tap would produce a 100% thread in an accurate hole of the same diameter as the minor diameter of its thread. Calculations based on a different standard formula for each thread may be used. Engineering handbooks and manufacturers give tables of tapping drill recommendations.
HOLES FOR TAPPING
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Major diameter
Minor diameter
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Figure 111
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Holes for Tapping Page: 230
Drilling swarf left in bottom of blind hole may cause tap to jam on packed swarf and break
Drill hole not round may cause tap to break
Drill hole too small may cause:- threads to break tap may break
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16.If the flutes are clogged, reverse the tap carefully and remove it from the hole. Use a brush to remove the chips from the tap and the hole and continue the tapping process. 17.Continue turning the tap until at least half the tap extends below the lower surface of the material. 18.When the taper tap reaches the required depth, change to the intermediate tap. Hand screw the intermediate tap into the thread drilled by taper tap and continue turning with the wrench. 19.To complete the hand-tapping, change to the bottoming tap after the intermediate tap reaches the required depth. Do it the same way as with the intermediate tap.
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Procedure 1. Check the size of thread required and select the correct taps. 2. Determine the correct size of tapping drill. Drill the tapping hole carefully and deburr the edges. 3. Fit the taper tap in a matching size bar-type tap wrench. 4. Hold the tap wrench with both hands close to the centre. Place the end of the tap in the hole. Sight up that the tap is perpendicular to the surface of the work. 5. Apply steady downward pressure and begin turning the handles clockwise in a horizontal plane. 6. Complete two turns while keeping the wrench handles level and applying even downward pressure. 7. Release and remove the tap-wrench, leaving the tap in place. 8. Place a small tri-square on the work to check that the tap is vertical to the work surface. Test again in a second position about 90˚ from the first. If the tap is not square to the surface, note the correction required. 9. Refit and tighten the tap-wrench. 10.Hold the tap wrench as before and begin turning. To correct a tap that is out of square, apply slight side pressure in the direction required as the wrench is turned. 11. Complete two turns and check as before that the tap is square. The tap must be square within the first few turns. Out of squareness cannot be corrected after this. 12.If the tap is square with the work, apply a suitable cutting fluid. 13.Hold the tap-wrench at the end of the handles with the fingers to allow sensitive feel of the torque applied to the tap. 14.Turn the wrench with constant pressure applied evenly with both hands. No downward pressure is required once the tap begins to feed itself into the hole. 15.As you turn the wrench try to feel the degree of resistance being offered to the tap. If you feel it is increasing, reverse the wrench a quarter turn. This will break off metal build-up.
HOW TO TAP
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Figure 112
How to Tap
Check tap is square
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Quarter reverse when necessary
Start tapping
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Complete tapping by constant turning
Squaring up the tap
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Effects of Lubrication Lubrication on threads has a significant effect on torque and great care should be taken when setting up torque wrenches to given values. Clarify whether the torque load specified is for wet or dry threads.
Toggle This type of torque wrench is set to a pre-determined torque prior to tightening the fastener. This is done by screwing the handle in or out, either S setting it to a scale along the wrench body, or S setting up in a rig.
Torsion Bar When a force is applied, a bar deflects in torsion (twisting) as well as bending. When the bar is twisted, a rack-and-pinion gear within the wrench is connected to a dial indicator which shows the amount of torque.
Deflecting Beam This consists of a square-drive at one end of an accurately-ground beam with a handle (mounted on a pivot) at the other end. A pointer indicates on a scale the amount of torque applied as the beam bends.
Types of Wrench There are three basic types of torque wrench S Deflecting Beam S Torsion Bar S Toggle
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Calibration Because torque wrenches and setting rigs are precision instruments, they are subject to periodic calibration testing. Depending on the frequency of use, this is either 6--monthly or annually, but if in very frequent use they should be checked on a weekly basis.
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General Torque is the amount of rotational force applied when tightening a fastener. To prevent over-tightening (and thus damaging threads), accurate application of torque is achieved by using a torque wrench. A torque wrench is a precision tool that either indicates torque applied or, through adjustment of the tool, prevents over-tightening. Depending on the range, a torque wrench is calibrated in inch-pounds or foot-pounds (Imperial) or Nm (metric).
TORQUE WRENCHES
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Toggle
Torsion Bar
Deflecting Beam
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Figure 113
Torque Wrenches
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Torque Analyzer
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ROTATING A NUT BY A VERY SMALL AMOUNT INCREASES THE TORQUE CONSIDERABLY. WITH THIS IN MIND, ALIGNING COTTER PIN HOLES SHOULD BE CARRIED OUT VERY CAREFULLY.
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Using Extension Bars Indicated torque on either a deflecting beam or torsion bar torque wrench is taken from the centre of the square drive. If an extension bar is to be used, its length must be taken into consideration (see calculation example).
CAUTION:
REMEMBER, TORQUE LOADING VARIES CONSIDERABLY BETWEEN WET AND DRY THREADS. THE VALUES IN THIS TABLE ARE FOR DRY THREADS. It is common practice to give a minimum and maximum value when specifying torque figures. In the case where a castle nut is tightened then secured with a cotter pin, always torque initially to the lower figure. Adjust the torque loading upwards (but not exceeding the upper value) to align the cotter pin hole with the nut castellation gaps. If this is unsuccessful, replace the washer for one with a different thickness and re-try.
CAUTION:
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The actual amount of torque applied to a fastener when a 5--inch extension is used with 120 pounds of indicated torque is 150 inch-pounds.
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Torque Values Torque values will normally be specified in the Maintenance Manual. If, however, no figure is given, the table opposite shows standard values.
TORQUE WRENCHES (CONT’D)
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Figure 114
Torque Values
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Metric Micrometer The bore of the barrel is screwed 1/2mm pitch and the spindle, which is attached to the thimble, screws through. Adjustment is provided for the longitudinal position of the spindle and for tightness of the screw head. The barrel is graduated in mm and 1/2mm for a length of 25mm and the rim of the thimble is divided into 50 equal divisions. Measurement is taken between the face of the anvil and the end of the spindle, and the range of the micrometer is 25 mm, so if we wish to measure up to 150 mm we must have six micrometers; 0 to 25, 25 to 50, 50 to 75 and so on with 125 to 150mm as the largest size.
Description A micrometer consists of a semi--circular frame having a cylindrical extension (barrel) at its right end, with hardened anvils inside, at the left end.
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Calibration Should the micrometer’s accuracy be in doubt (or it is due periodic calibration), it can be checked and readjusted. This is accomplished by using a standard or gauge block; a piece of metal or ceramic that is manufactured to very close tolerances which itself is subject to routine calibration. The gauge block is inserted between the anvil and spindle and the spindle then closed gently onto the block. The tool is then adjusted by means of a wrench (supplied with the micrometer) so that the zero mark on the thimble exactly coincides with the sleeve datum line. Calibration/adjustment is normally carried out by a specialist in a temperature/humidity controlled environment.
Imperial Micrometer In this case, the pitch of the screw thread on the spindle is 40 threads per inch. One revolution of the thimble advances the spindle face toward or away from the anvil face precisely 1/40“ or .025“. The reading line on the sleeve is divided into 40 equal parts by vertical lines that correspond to the number of threads on the spindle. Therefore, each vertical line designates 1/40“ or .025“. Lines vary in length for easy reading. Every fourth line, which is longer than the others, designates a hundred thousandths. For example, the line marked „1“ represents .100“ and the line marked „2“ represents .200“ etc. The bevelled edge of the thimble is divided into 25 equal parts, with each line representing .001“ and every line numbered consecutively. Rotating the thimble from one of these lines to the next moves the thimble longitudinally 25 of .025“, or .001“. Rotating two divisions represents .002“ etc. 25 divisions indicate a complete revolution of .025“ or 1/40 of an inch.
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General When a part has to be measured to the second decimal place in the metric system (or the third place in the English system), a more accurate method of measurement is needed than can be obtained with a vernier calliper, so a micrometer is commonly used.
MICROMETER
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1
2
1. Anvils 2. Spindle 3. Locknut 4. Sleeve 5. Main nut
11
3
4 9
5 6
7
Figure 115
Micrometer
6. Adjusting nut for main nut 7. Thimble adjusting nut 8. ratchet stop 9. Thimble 10. Frame
Index to parts
10
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Reading Example The thimble has moved out 8 complete turns = 1 additional half-millimetre division is visible = 36 thimble lines have passed the datum line = Reading = 8.00 0.50 0.36 8.86mm
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Reading Example The thimble has moved out 3 complete turns = 2 additional 0.025“ divisions are visible = 12 thimble lines have passed the datum line = Reading =
0.300 0.050 0.012 0.362 in
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Micrometer Readings - Imperial The screw in the metric micrometer has a pitch of 0.025 in, so that the jaws open 0.025 in (1/40 in) for each revolution of the thimble. The rim of the thimble is divided into 25 divisions, each of which gives a reading of 0.001 in. The barrel is marked in 0.1 in and 0.025 in divisions, so that to take a reading we add the number of thousandths indicated on the thimble to the tenths and hundredths uncovered on the barrel.
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Micrometer Readings - Metric The screw in the metric micrometer has a pitch of 0.5mm, so that the jaws open 0.5mm for each revolution of the thimble. The rim of the thimble is divided into 50 divisions, each of which gives a reading of 0.01mm. The barrel is marked in millimetres and 0.5mm divisions, so that to take a reading we add the number of hundredths indicated on the thimble to the millimetres and half-millimetres uncovered on the barrel.
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Imperial
Metric
8 = 8.0
= 0.36
=.300
Reading Examples
=.012 Measurement = .362 in
Lines on thimble which have passed sleeve datum line ..... 12
Lines (bottom) visible between 3 and thimble edge ..... 2 (2 x .025) =.050
Highest number (top) visible on sleeve ................................ 3
Figure 116
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Measurement = 8.86mm
Lines on thimble which have passed sleeve datum line ..... 36
Lines (bottom) visible between 8 and thimble edge ...... 1 (1 x 0.50) =0.50
Highest number (top) visible on sleeve ...............................
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20 Complete Turns 20 x 0.50 = 10.00 mm Plus 50 x 0.01 = 0.50 mm Reading is 10.5 mm
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Figure 117
13.00 mm Plus 0.01 mm 13.01 mm
Reading Examples (Continued)
26 x 0.50 = 1 x 0.01 = Reading is
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..... x 0.50 = ..... x 0.01 = Reading is
.......... mm Plus ......... mm .......... mm
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USE ONLY THE RATCHET STOP, OTHERWISE THE MEASUREMENT WILL BE INACCURATE DUE TO OVERTIGHTENING.
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NOTE:
Micrometer handling 1. Set the micrometer to a oversize dimension 2. Set the frame anvil straight to the work 3. Clamp the spindle against the subject using the ratchet stop
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Tighten using the ratchet stop
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Figure 118
Handling on hard-to-get locations or one-hand handling
Micrometer Handling
Micrometer mounted on a stand (use when you have to measure a lot of objects)
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Description The vernier calliper consists of a bar and two measuring jaws. One jaw is fixed to the bar, the other one slides on the bar. The bar of a metric vernier calliper is equipped with an engraved scale, graduated in mm. Opposite to this scale there is the vernier scale on the slide. This scale is divided in 10, 20, or 50 equal spacing, known as 1/10, 1/20 or 1/50 vernier.
General Vernier callipers / sliding gauges are used to make accurate inside or outside as well as depth measurements faster than those made with a micrometer, and for measurements that exceed the practical range of a micrometer.
VERNIER CALLIPER
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1 2 3 4 5
Figure 119
Reference surface Main scale Vernier scale External measuring jaws Step measuring face
Vernier Calliper
6 7 8 9 10
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Internal measuring jaws Clamp screw Slider Depth bar Main beam
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1/50 Vernier The accuracy reading is 0.02mm.
1/20 Vernier The most often used vernier calliper is the calliper with the 1/20 vernier and an accuracy reading of 0.05mm.
1/10 Vernier The distance from 0 to 1 on the main scale is 10mm and it will be seen that 10 divisions on the sliding vernier scale are equal to 9mm on the top main scale. The length of the bottom division is 9mm: 10 = 0.9mm, and since the top division is 1mm, the difference is 1mm -- 0.9mm = 0.1mm. This difference represents the accuracy to which readings may be taken.
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1/10 Vernier
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Figure 120
Vernier
1/20 Vernier
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1/50 Vernier
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Count the total length indicated on the main scale and note the mark on the vernier scale which is level with a mark on the main scale. This latter amount will represent the number of dimensions which must be added to the first reading.
Vernier Calliper Readings Readings are carried out as follows:
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Figure 121
Principle of a Vernier
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Figure 122
Vernier Examples
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Figure 123
Vernier Reading
Reading is 68.32 mm (1/50 Vernier)
Reading is 73.65 mm (1/20 Vernier)
Reading is 30.00 mm (1/10 Vernier)
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Figure 124
Vernier Reading Examples 1
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Reading .......... mm
Reading .......... mm
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Figure 125
.......... inches
.......... inches
Vernier Reading Examples 2
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Reading .......... mm
Reading .......... mm
.......... inches
.......... inches
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Depth measurement Ensure that the recess in the depth gauge is in the corner area.
Outside Measurement Set the fixed leg against the work and slide the movable leg to the final position. Set the starting position with the vernier calliper in the oversize dimension until in place.
Vernier Calliper Handling The vernier calliper is made in various sizes from 150mm upwards, a useful size being one capable of working up to 300mm. When it is used for a bore or any other inside measurement, set the cross jaws to an undersize dimension and slide it to the final position.
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✘
Internal Measurement
✔
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Take the smallest reading (groove).
✘
✔
Take the maximum reading (internal diameter).
Insert jaws as deep as possible into workpiece.
✘
Measurement Force Do not apply excessive force to the workpiece. This can result in inaccurate measurement due to positional deviation of the calliper jaws.
✘
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✔
Figure 126
✘
Vernier Measuring Precautions
✔
Set the depth bar perpendicular to the measured surfaces.
✘
Depth Measurement
Parallax Error When taking the reading, ensure you view the scale perpendicular to the measured point. When viewed obliquely (direction A) parallax error occurs, resulting in inaccurate reading.
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✔
✘
Page: 256
Align the step measuring face with the surface of the object.
Step Measurement
✔
Outside Measurement Place the workpiece as deep as possible into the jaws, ensuring the faces are square to the object being measured.
✘
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Description One revolution of the large hand corresponds to 1mm. The second smaller hand of the rotation tachometer counts the revolutions of the large hand. Measuring range is normally 10mm. Set to zero by revolving the rotary scale.
General The dial indicator is a high-precision measurement tool with an accuracy of 0.01mm. It is especially used in the mechanical engineering section to measure alignments of shafts or to check the smoothness of surfaces. A special type of dial indicator is an excellent tool to measure material removed after corrosion or lightning-strike repairs.
DIAL INDICATOR
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Pin
Spindle
Figure 127
Tolerance marks
Dial Indicator
Climb shaft
Rotation tachometer (mm)
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THIS PROCEDURE MEASURES THE DEPTH OF THE MATERIAL REMOVED. THE THICKNESS OF THE MATERIAL REMAINING MUST BE FOUND OUT BY CALCULATION.
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NOTE:
4. Carry out the inspection at different points in the inspection area until you find the maximum depth of removed material.
3. Use of the dial gauge for inspection is as shown.
2. Put the dial indicator with the measuring stand on a flat surface and rotate the rotary scale mark to zero.
Work sequence 1. Clean up damaged area.
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Figure 128
Dial Indicator Work Sequence
Area where you must remove the paint
Base flat on skin
Dial gauge
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Skin
Measuring stand
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Description The off-hand grinding machine is basically an electric motor with grinding wheels mounted onto the spindle (normally one on either side). It is common practise to have different grade wheels; one for rough finishes and the other for finer grinding. Grinding machines can be either bench- or floor-mounted. Floor-mounted (or pedestal) grinding machines often have a tank mounted on the front containing some sort of queching fluid (usually water). Excessive grinding of items without periodic cooling can destroy it’s tempering.
NEVER USE THE SIDE OF AN ABRASIVE WHEEL; A GROOVE CAN FORM OVER TIME, CREATING A WEAK POINT THAT HAS, IN THE PAST, LED TO WHEELS EXPLODING. Over a period of time, the surface of the wheel will become grooved and pitted and embedded with metal. A specially-trained operative will dress the wheel using a diamond-tipped tool.
CAUTION:
Safety An off-hand grinding machine is potentially very dangerous, so approximately 3/4 of the circumference of the wheel is encased in the wheel guard. Additionally, there is a transparent screen covering as much of the exposed part of the wheel as is practical. Despite this screen, always protect your eyes with goggles as well. The tool rest should be adjusted to give the smallest possible clearance between it and the wheel.
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CAUTION:
Page: 261
THE POINT OF A PUNCH SHOULD ALWAYS BE GROUND WITH THE GRINDING LINES PARALLEL TO THE AXIS. TRANSVERSE GRINDING WEAKENS THE POINT.
Grinding a Centre Punch 1. Hold the punch in one hand and position the fingers of the other hand towards the head of the punch so that it can be rotated during the grinding operation. 2. With the first hand steadied against the tool-rest, adjust the angle of the punch so that it is approximately 60o to the face of the wheel. 3. As you touch the point of the punch on the wheel, maintain a light, even pressure and rotate the punch. 4. Quench the punch frequently to prevent over-heating and subsequent softening of the metal.
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Introduction The abrasive wheel is made of abrasive materials bonded together. Most wheels are made from silicon carbide (carborundum), but aluminium oxide abrasives are occassionally used for fine grinding.
ABRASIVE WHEELS
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Tool rest adjuster
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Tool rest
Grinding wheel
Drive motor
Wheel guard
Screen
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Figure 129
Screen
Off-Hand Grinding Machines
Quenching fluid
Goggles
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Pedestal Grinding Machine
Quenching tank
Bench Grinding Machine
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What is mineral oil and why is synthetic oil different? Mineral oil is derived from crude oil, which is extracted underground from rock structures. In the industry, we call mineral oil a base oil or a base stock, simply because it forms the base of a formulation. To manufacture base oils, crude oil is heated up and the evaporated material collected at different temperatures (atmospheric distillation). The material collected is then vacuum distilled, processed through a furfural extraction unit to remove aromatic components and solvent dewaxed to remove wax crystals. Hydrofinishing is then undertaken to remove impurities and make the base oil brighter. Synthetic oils are manufactured by chemical reaction and can produce very consistent quality base stocks of different viscosities depending on the molecular weight of the material produced. The key differences are that mineral base stocks contain some impurities, are less molecularly pure and less thermally stable than equivalent synthetic oils. However, catalytic techniques are making special base stocks almost identical to synthetic oils. Interestingly, it has been found that impurities in mineral base stocks can enhance certain performance aspects, for example anti--oxidant properties.
LUBRICANTS ARE GENERALLY VOLATILE AND SHOULD BE STORED IN LOCKERS AND AREAS DESIGNED TO MINIMISE THE POSSIBILITY OF FIRE.
CAUTION:
Page: 263
LUBRICANTS SHOULD NOT BE MIXED; COMPONENT SEALS ARE CHOSEN FOR THEIR COMPATIBILITY WITH A SPECIFIC LUBRICANT. INTRODUCING AN INCORRECT LUBRICANT CAN BREAK DOWN A SEAL, DESTROYING ITS EFFECTIVENESS. OILS AND GREASES SHOULD BE KEPT IN CLEARLYMARKED CONTAINERS, PREFERABLY THAT IN WHICH THEY ARE RECEIVED FROM THE MANUFACTURERS. OIL CANS AND GREASE GUNS SHOULD BE CLEARLY MARKED WITH THEIR CONTENTS.
CAUTION:
Oil or Grease? The Maintenance Manual will indicate the correct lubricant, method and frequency of application.
Personal Safety Oil and grease in contact with the skin can result in dermatitis. Barrier cream should be applied prior to handling these lubricants. The accidental subcutaneous injection of oil or grease can also have serious health implications. Oiling and greasing equipment should be handled with care and horseplay can result in disciplinary action.
Methods of Application Oils and greases are normally applied via oil cans and grease guns, whereby the lubricant is pumped into the area requiring it. Usually the lubricant is hand-pumped, but large grease drums can be fitted to pneumatic devices to facilitate greasing of multiple points.
What are lubricants ? Lubricants control friction and wear by introducing a friction-reducing film between moving surfaces in contact. They may be fluid, solid or plastic. Lubricants are generally formulated for specific applications. For example, engine oils. In this application, they reduce fiction and so increase fuel efficiency, reduce wear of moving parts, protect the inside of the engine against corrosion, cool the piston and other hot components, remove combustion impurities and blow--by gases and help seal the piston during combustion, thus improving energy conversion. Lubricants are highly sophisticated products, not easily formulated.
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What is grease? Grease is a lubricant composed of an oil or oils thickened with a soap or other thickener to make a solid or semi--solid product.
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Introduction To prevent heat build-up, increase efficiency and prolong component life, moving parts must be lubricated.
LUBRICATION
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Lumatic Minor HP Grease Gun
Filling handle
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Operating lever
Pressure spring
Grease container
Plunger piston
High pressure piston
Outlet tube assembly
Air release valve Lubricating connector
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Figure 130
Filling handle
Light alloy head
Non-return valve
Plunger piston
Pressure spring
Lubrication Tools
Wanner HP Grease Gun
Operating lever
Lubricating connector
High pressure piston
Outlet tube assembly
Transfer valve
Air release valve
Grease container
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Oil container
Pump assembly
Application spout
Oil Can
Pump operating lever
Page: 264
Handle
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Special Performance Greases Special performance greases include: S Royco 11MS S MIL--PRF--81322 (NATO G--354) S BMS 3--24. In some applications, a special purpose grease is necessary. Where only one grease is recommended for a specific application, it will be listed with the word ”Only” after it.
General--Purpose Aviation Grease Boeing selects the grease to use based on the specific application. Greases that meet the following specifications are considered general--purpose aviation grease for the --100oF (--73oC) to 250oF (121oC) range: S BMS 3--33 S MIL--PRF--23827 S MIL--G--21164 (NATO G--353). BMS 3--33 is the preferred general--purpose aviation grease recommended by Boeing for applications exposed to temperatures of less than 250oF. It is recommended because it shows better wear, corrosion protection and low temperature torque properties. Greases that have been used before and approved by Boeing for the specific assembly are listed as flagnotes on the lubrication instructions for the specific assembly. If there is an application where only one grease must be used, it will be listed with the word ”Only” after it.
General Instructions for Lubrication This section of the AMM gives the normal aircraft lubrication procedures. Specific data about where to lubricate is given in the subsequent subjects of this section. There are other lubrication instructions in other ATA sections of the AMM about equipment removal and replacement.
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Page: 265
Lubrication Application Procedures and Cautions Do the following to prevent lubricant contamination: S Put lubricant identification labels on all containers, guns and dispensers. S Keep lubricants in containers that have tight covers. S Make sure that the container material will not absorb contamination. S Keep out dust and other contamination when the container is open. S Keep grease guns, brushes and oil cans clean.
Lubrication Symbols Lubrication blocks are used to show the part or unit to be lubricated. Examples of lubrication blocks used in the manual are shown opposite. If necessary, more data is given near the lubrication block to help you lubricate the airplane correctly. Each block shows this data: S The lubrication method S The type of lubricant S The access panel number is given above or below the lubrication block for points if it is not easy to find the area you must lubricate. More data on commonly-used grease is available in Boeing Service Letter 737--SL--20--027, Summary of Most Commonly Used Greases on Boeing Airplanes.
Other Lubricants S BMS 3--32, Type II Landing Gear Shock Strut Fluid, Anti--Wear S MIL--H--5606, Hydraulic Fluid, Petroleum base, Aircraft (NATO H--515) S MIL--PRF--7870, Lubricating Oil, General Purpose, Low Temperature (NATO O--142).
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GENERAL LUBRICATION INSTRUCTIONS - BOEING
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Figure 131
Lubrication Symbol Examples
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Correct Lubrication Do not S let dirt, swarf and other unwanted material get in the lubricant during and after lubrication. Remove dirt from the grease fittings before you attach the grease gun. S lubricate Teflon bearings and bushings; lubricants may cause damage to the Teflon and decrease the bearing life. S push the seal out with the grease. Do S ensure that the pressure that you set is less than 2500 psi (17237 KPa). Too much pressure will cause the fitting to blow out, resulting in injuries to personnel and/or damage to equipment. S set the pressure at 100 to 200 psi (689 -- 1379 KPa) unless otherwise specified. This is usually sufficient to push out used grease. S find all of the lubrication points that are identified in the specific maintenance task. S use the specified lubricant. S use an Alemite Midget flush adapter (No. 314150) for flush--type grease fittings. S apply all lubricants slowly and smoothly. S dispense grease into the grease fitting until the used grease is visually removed and only new grease comes out. S remove unwanted grease or lubricating fluid that is around the part or on other parts to prevent contamination and damage to other surfaces. S be careful when you lubricate sealed--ball or sealed--roller bearings that have a grease fitting. S Use a restrictor--type adapter to decrease the flow rate of the grease. S Stop the operation if the shape of the seal starts to change, or if the grease comes out of the bearing. If a grease fitting comes out, carry out the following: S Look for blockage in the fitting or part. S If necessary, dismantle the part to remove the blockage. S Install a new fitting (AMM TASK 20--10--24--421--001).
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Alemite Midget 31450
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Figure 132
B737 Main Landing Gear Lubrication Example
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PUT THE LUBE FITTING INTO THE HOLE IN THE MATING PART AS QUICKLY AS POSSIBLE SO THAT IT DOES NOT WARM UP TOO MUCH. 7. Let the lube fitting cure for 12 hours at room temperature before using it.
NOTE:
Installation Of A Lubrication Fitting Which Has Blown Out 1. Get the specified standard size or a modified size lube fitting for installation. 2. Clean the lube fitting hole as follows: A. use cotton swabs to remove as much grease as possible from the lube fitting hole. B. use cleaner on a clean cotton swab to clean the hole to a depth of 1/2 in minimum. 3. Carry out the following steps to apply the primer: A. Use a cotton swab to apply a thin coat of primer to the bore of the hole. B. Let the primer air-dry at room temperature for a minimum of 5 minutes before you apply the retainer compound. 4. Use a cotton swab to apply a thin coat of adhesive to the bore of the hole. The depth of the adhesive should be 0.25 to 0.40 inch. 5. Put the lube fitting into liquid nitrogen for a minimum of 1 minute to ensure the lube fitting cools equally. 6. Use the correct driving tool to fit the lube fitting into the hole in the mating part.
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ENSURE YOU USE THE CORRECT TOOL TO INSTALL THE LUBRICATION FITTING. DRIVE THE LUBRICATION FITTING IN STRAIGHT TO PREVENT DAMAGE TO THE MATING SURFACES. 1. Get the specified standard lube fitting for installation. 2. Clean the lube fitting hole as follows: A. use cotton swabs to remove as much grease as possible from the lube fitting hole. B. use cleaner on a clean cotton swab to clean the hole to a depth of 1/2 in minimum. 3. Use the correct driving tool to fit the lube fitting into the hole in the mating part.
CAUTION:
Lubrication Fittings -- Installation
EXAMPLE: B737 LUBRICATION FITTINGS REMOVAL/INSTALLATION
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Figure 133
Lubrication Fitting Modification and Installation
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DO NOT OPERATE POWER--OPERATED LUBRICATION EQUIPMENT AT MORE THAN 103.5 BARS (1500 PSI). HIGH LUBRICATION PRESSURE CAN CAUSE DAMAGE TO THE AIRCRAFT. S Lubricate the MLG uplock, Item No. 5 of the MLG Door and Uplocks Table, with COMMON GREASE (Material No. 04--004) as follows: Lubricate the greasers Items 1 thru 4 in the Main Landing Gear Door and Uplock Table with COMMON GREASE (Material No. 04--004) until new grease comes out. If you use hand--operated lubrication equipment, lubricate each greaser with a maximum of two full strokes. Remove the unwanted grease: S clean the greasers with a clean MISCELLANEOUS (Material No. 19--003) and CLEANING AGENTS (Material No. 11--026). S ensure that the greaser ball has seated correctly.
CAUTION:
USE THE TABLES THAT FOLLOW TO DETERMINE THE CORRECT GREASER. Lubricate the MLG Uplock:
NOTE:
MLG Lubrication
Equipment Preparation 1. Ensure that the lubrication equipment is in a serviceable condition before you fill it. 2. Operate the lubrication equipment to make sure that the lines and adaptor are full of new lubricant. 3. Clean the greasers with a clean MISCELLANEOUS (Material No. 19--003) and CLEANING AGENTS (Material No. 11--026).
MLG and Doors Lubrication No specific lubrication equipment required.
EXAMPLE: A320 MLG AND DOORS LUBRICATION
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Figure 134
Greaser Table
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Figure 135
Greaser Table (Cont’d)
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Figure 136
Lubrication Points
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Bonding Connections When a bonding connection is to be made or renewed, it is essential that the conductor has the specified current-carrying capacity. Braided copper or aluminium cords fitted at each end with connecting tags or lugs (’bonding jumpers’) are used for bonding connections between moving parts or parts subjected to vibration. All bonding connections must be properly locked to prevent intermittent contact which may be caused by vibration. Intermittent contact is worse than no contact at all. Bonding connections must not interfere (either mechanically or electrically) with any associated or adjacent equipment, nor should they be excessively tight or slack. Provided that all insulating materials (anodic finish, paint etc) are removed from contact faces before assembly, the following joints are considered self-bonding: S metal-to-metal joints held together by threaded devices or rivets S most cowling fasteners, locking and latching mechanisms S metal-to-metal door and panel hinges S metal-to-metal bearings
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Secondary
Primary
Bonding Classification
Between equipment containing circuits carrying 50 volts (rms or dc) or more, and the main earth system.
1 ohm
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0.5 megaohm or 100,000 ohms per sq ft of surface area (whichever is the less)
Between all isolated conducting parts which may be subject to appreciable electrostatic charging and the main earth system. Between equipment supplied fromthe unearthed system, of any voltage, and the main earth system.
1 ohm
0.05 ohm
Estimated and declared by manufacturer.
Maximum Resistance
Between metallic parts normally in contact with flammable fluids and main earth system, and also between the parts themselves.
Between bonded components and portions of main earth system to which they are connected.
Between extremities of the fixed portions of metallic aircraft.
Between extremities of the fixed portions of aircraft of non-metallic or composite construction.
Test Condition
Resistance Values The Civil Aviation Authority’s requirements with regard to the maximum resistance values for the various conditions of bonding are summarised here.
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Bond Testing Bonding is the electrical interconnection of metallic parts (normally at earth potential) for the safe distribution of electrical charges and currents. Bonding provides a means of protection against charges as a result of the build-up of precipitation, static and electrostatic induction (as a result of lightning strikes) so that the safety of the aircraft and its occupants is not endangered. Bonding also reduces the possibility of electric shock from the electrical supply system, reduces interference with the functioning of essential services (radio communications and navigational aids) and provides a low-resistance electrical return path for electric current in earth-return systems. The aircraft’s earthing system is automatically connected to the ground upon landing via the nose (or tail) wheel tyre, which is impregnated with an electrically conducting compound.
ELECTRICAL TEST EQUIPMENT
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Milliohmmeter
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Figure 137
Electrical Test Instruments
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Voltmeter
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Method 1 1. The 60--foot cable should be connected to main earth (also known as the bond datum point) at the terminal points usually shown diagrammatically in the relevant Aircraft Maintenance Manual. Since the standard bonding tester lead is 60 feet, the measurement between the extremities of larger types of aircraft may have to be done by selecting one or more main earth points successively, in which case the resistance value between the main earth points should be checked before proceeding to check the remote point. 2. The 6--foot cable should be used to check the resistance between selected points, usually specified in the bonding test schedule or the Aircraft Maintenance Manual. When the two spikes of the test lead probe are brought into contact with the aircraft part, the test-meter will ndicate, in ohms, the rsistance of the bond.
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Excessive Resistance 1. In the case of bonding jumpers, the connecting tag or lugs should be removed and the contacting faces thoroughly cleaned, using a slight abrasive if necessary. All traces of abrasive must be removed. The connecting area should be sealed and treated with anti-oxidant as specified in the relevant drawing and specification. 2. If a holding bolt is the bonding connection, the bolt should be removed and the area under the bolt-head (or nut) cleaned and protected as above. 3. If the required bond value cannot be obtained at a structural joint, the advice of the manufacturer must be sought. Note: corrosion tends to form at a bonding or earth connection and is often the cause of excessive resistance.
Method 2 Alternatively, the four-terminal method of resistance measurement may be adopted with the appropriate miliohmeter (see Fig 1). The test leads may be in the form of duplex spikes (see Fig 2) or, when used in association with crocodile-type test leads, single spikes. Note: In order to check that the instrument is functioning correctly, the two hand spikes should be placed on a low-resistance conductor with the potential spikes (P1 and P2) closely together (see Fig 3). The result of this test should be a zero reading on the meter. 1. A test current (approx 2 amps) is supplied via the internal batteries and passed through the resistance via cables C1 and C2. 2. The voltage drop across the rsistance is measured (P1 and P2) and compared with the current flowing. The resultant value is then displayed (normally digitally) on the meter. Note: To ensure good electrical contact at the probe spikes, it may be necessary to penetrate or remove a small area of a non-conducting protective coating. Therefore any damage to the protective coating must be restored after the test.
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Bond Testing (Cont’d) Special test equipment, consisting of a meter and two cables each of specific length, is required for checking the resistance of bonding. A meter commonly used consists of an ohmmeter operating on the current ratio principle and a single 1.2 volt nickel-alkaline cell housed in a wooden carrying case. The associated cables are 60 feet and 6 feet in length and are fitted with a single-spike probe and a double-spike probe respectively. Note: prior to testing, a check should be made on the state of the cell by observing: S that a full-scale deflection of the meter is obtained when the two spikes of the 6--foot cable probe are shorted S that the meter reads zero when the two spikes of the 6--foot probe are shorted by the single spike of the 60--foot probe.
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P
Figure 138
Bond Testing Methods
Fig 3: Test Position of Hand Spikes
P
LOW RESISTANCE CONDUCTOR
P1
Resistance
P2
C2
P
Fig 2: Duplex Hand Spikes
P
C1
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Fig 1: Four Terminal Resistance Measurement
Resistance
C1 P1 P2 C2
Ohmmeter terminals
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of potential spikes
NOTE: observe position
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Millivolt Drop Test Excessive resistance in high-current carrying circuits can be caused by loose terminal connections, poorly swaged lead ends etc. Faults of this kind are indicated by low terminal voltage at the connections to the service load and by heating at a conductor joint. If such faults are suspected, a millivolt drop test is recommended. For continuously-rated circuits, the test should, whenever possible, be made with the normal operating current flowing, the power being derived from an external source. For short-rated circuits, a suitable resistance or other dummy load should be used in lieu of the normal load and the current should be scaled down to avoid overheating. The millivolt-meter should be connected to each side of the suspected joint and a note made of the volt drop indicated. The indicated reading should be compared with the figures quoted in the relevant publication (an approximate guide is 5 mV/10 amps flowing).
Continuity Testing A concealed break in a cable core or at a connection may be found by using a continuity tester, which normally consists of a low-voltage battery (2.5 volts) and a test lamp or low-reading voltmeter. Before testing, the main electrical supply should be switched off or disconnected. Check that fuses are intact and that there is no intermediate disconnection. Switches and circuit-breakers, as appropriate, should be closed to complete the circuit. When carrying out a low-voltage continuity check, it is essential to work progressively through the circuit, commencing from the relevant fuse or circuit breaker and terminating at the equipment. Large circuits will probably have several parallel paths and these should be progressed systematically, breaking down as little as possible at plug and socket or terminal block connections.
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M 7.5 ENGINEERING DRAWINGS
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GENERAL Drawings are normally drawn to a uniform scale which is stated on the drawing and is usually shown in a SCALE BOX by a ratio e.g. 1:1 (full size), 1:2 (half size), etc. In practice, no drawing should be measured to obtain a dimension which is not shown. Drawings to scale 1:1 would be too large to handle comfortably, so they are generally printed smaller for convenience. During this ’shrinking’ process actual dimensions can become distorted, so taking a measurement directly from the print would invariably be inaccurate. If a particular dimension has been omitted, enquiry must be made to the Design Office or appropriate authority for the information.
SCALE
Standards Other standards encountered when reading aircraft engineering drawings include. ISO, international standards organisation and MS, military standard.
The layout, content and numbering system for aircraft engineering drawings is decreed by Specification 100 of the Air Transport Association of America. This topic is expanded on in Section M7.20 Maintenance Procedures.
AIRCRAFT ENGINEERING DRAWINGS
DRAWING PRACTICES To understand drawings, the engineer must be familiar with common drawing practices. The most common practices will be explained in the following pages and will include the important aspects of:-1. scale 2. use of lines 3. methods of presentation 4. types of projection 5. special views.
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INTRODUCTION Engineering drawing is the language of engineers. Drawings convey the designer’s requirements in a much clearer way than could be done by the use of words. Drawings are widely used and must include sufficient information to enable manufacture, assembly, production planning, testing and inspection of the particular component, or assembly, to be carried out. A British Standard (BS308) lays down criteria and conventions which should be adhered to when creating an engineering drawing. As well as showing the shape by drawing, the actual size of the shape must be given. For reasons that will be explained later, engineers do not measure drawings to determine sizes, they refer to dimensions which are given on the drawing. The engineer will need to know the finish required on the material. He must, of course, also know the specification of the material from which the component is to be made. if you have previously used drawings your list may have been completed as follows: S shape S size or dimensions S material specification S material finish S relationship between the component and associated components in an assembly. Additionally, data should be provided regarding: S method of manufacture S assembly/disassembly sequence S installation and operation
ENGINEERING DRAWINGS (GENERAL)
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Figure 139
SCALE
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1:1
DATE
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Traditionally, the list of all component parts on a drawing are listed above the title block. It is also known as the ’Bill of Materials’. Multi-sheet drawings may have many parts, so to reduce clutter and for convenience they usually have separate ’BoM’ sheets reflecting all the parts, their part numbers, their locations (by zone) and their effectivity (which mark of aircraft they are fitted to).
PARTS LIST (BILL OF MATERIALS)
Prototype aircraft drawings are not formally released until the aircraft type goes into production. Then the drawing will be detailed as ’Issue 1’. From time to time, amendments are made to engineering drawings, for example if an item is modified in some way, or perhaps a new component is added. This amendment must be recorded on the drawing, as it is important to be working from the latest issue of an engineering drawing. This revision process is known as ’raising-in-issue’ and the drawing issue will increase by one digit, ie from Issue 1 to Issue 2. Conventionally, the Revision Block starts in the top right-hand corner of each sheet and subsequent amendments are recorded to the left.
REVISION
Aircraft drawings are very large and often run over many sheets. As can be seen on the diagram opposite, a drawing is bounded by a grid system similar to a map. Typically, the vertical divisions are marked with letters and the horizontal numbers. A combination of a vertical and horizontal coordinate indicates a zone. The zone can be used to locate sections and parts on large drawings. For example, Zone D-1 in the diagram opposite shows the position of the Revision Block. With multi-page drawings, reference will be made to the map reference on the relevant sheet, ie D-1--2 (the ’2’ being the sheet number).
Every print must have some means of identification. This is provided by the title block. The title block consists of a drawing number and certain other data conceming the drawing and the object It represents. This information is grouped in a prominent place always in the lower right--hand side of every sheet. When a print is correctly folded, the title block is on the outside for easy reference. The title block on Boeing production drawings contains the following information: S DRAWING NUMBER: The drawing number is in 1/2--inch--high characters. S TITLE: The title of a drawing is in 1/4--inch--high characters. S SCALE: The scale of which the majority of views and sections are drawn is entered as a ratio. When various parts are drawn to different scales, or if there is no picture on Sheet One, the word ”NOTED” is entered. S DIMENSIONAL TOLERANCE NOTES: Preprinted here are the general tolerances to be used with the various drawing dimensions if a tolerance is not otherwise shown on the drawing. S SH of : The total number of sheets is shown with the consecutive sheet number such as SH 1 of 1, SH 1 of 4. On drawings with an automated parts list (APL), this entry does not include the total number of picture sheets. The application block of the separate parts list lists all applicable sheets for each item. S SIGNATURES: The ”signature” block Is a list of approval signatures for the drawing. S SECT NO: The section number of the aircraft in which the item is installed. when an installation extends through several sections ”MS” Is used for multisections. S USED ON: The basic model number.
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ZONES
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TITLE BLOCK
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Figure 140
The drawing number should appear in the top left--hand corner as well as bottom right.
M7 MAINTENANCE PRACTICES ENGINEERING DRAWINGS, DIAGRAMS AND STANDARDS
Engineering Drawing - Standard Layout
The title block -- normally standardised by the manufacturer -- contains all the general information relevant to the drawing.
The parts table only applies when the drawing shows two or more components assembled together. All parts (both ’bought in’ and manufactured should be listed.
Tables are arranged so that part numbers and revision letters build up from the border inwards to allow for future additions to the drawing.
Full details of all modifications should be listed in the revision table.
Zone references are provided for quick and easy location of revisions (modifications).
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GENERAL Different types and thicknesses of lines are used on drawings for the purposes as shown in the table opposite.
TYPES AND USE OF LINES
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Limits of partial or interrupted views and sections
Limits of partial or interrupted views and sections
Hidden outlines and edges
Continuous thin irregular
Continuous thin straight with zigzags
Dashed thick
Types And Use Of Lines
Outlines and edges of adjacent parts, alternative and extreme positions of movable parts, centroidal lines, initial outlines prior to forming, bend lines on developed blanks or patterns
Chain thin double dashed
Figure 141
Lines or surfaces to which a special requirement applies
Cutting planes
Centre lines, lines of symmetry, trajectories, pitch lines and circles
Chain thick
Chain thin, thick at ends and changes of direction
Chain thin
Hidden outlines and edges
Imaginary lines of intersection, dimension lines, projection lines, leader lines, hatching, outlines of revolved sections, short centre lines
Continuous thin
Dashed thin
Visible outlines and edges
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Continuous thick
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BREAK LINES Because of limited space on a sheet of drawing paper, and so as to produce a compact drawing, the use of break lines is often practised as shown on the graphic below.
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Break Lines
Rectangular (wood)
Round Tube
Figure 142
Rectangular
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Round Bar
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REPETITIVE INFORMATION Where several features are repeated in a regular pattern, such as rivets, bolts or slots, only the number required to establish the pattern may be shown, by marking their centerlines. Any further information may be given in a note. The graphic below shows a typical skin joint which could be drawn in this manner.
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Figure 143
Repetitive
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Holes As can be seen opposite, holes can be plain--drilled, reamed or threaded. S Drilled holes are portrayed by a thick--lined circle. Its diameter may be shown by a note. If the hole is ’blind’ the note will include the depth. Fastener holes are often shown as symbols with an accompanying explanatory table. S Reamed holes symbols will include an explanatory note differentiating them from plain holes. S Threaded holes are defined with a thick circular line for the thread crest and a thin, broken one for the root.
Introduction To minimise confusion, certain conventions have been adopted to standardise the way items appear on engineering drawings.
SYMBOLS
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Straight--through hole
Common Drawing Symbols - Holes
A hole may incorporate one or more features, as in this case (spotfaced, threaded and countersunk).
Reamed Hole
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Figure 144
Blind hole
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Threaded Hole
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Holes can be counterbored, spot--faced or countersunk to accomodate fastener heads for flush fitting. S A counterbore is a larger diameter hole, concentric to the primary hole, with a flat shoulder. It is portrayed in plan view as two concentric thick--line circles. S A spotface is effectively a shallow counterbore to provide a flat, smooth seating for a mating part or for a fastener head or nut. It is necessary when the casting has a rough finish or is not square to the hole. It is portrayed in plan view just like a counterbore, but the diameter of the spotface must be given. The depth is not given; it is the minimum necessary to achieve a flat seating. S Countersunk holes accept the tapered head of a fastener and are created by special countersinking bits. It is portrayed in plan view by two concentric thick lines, with details of the hole and the angle and diameter of the countersink.
SYMBOLS - RECESSED HOLES
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Counterbored Hole
Figure 145
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Spotfaced Hole
Common Drawing Symbols - Recessed Holes
Countersunk Hole
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The figure opposite shows some typical conventions used in engineering drawings. These are, however, just a few used.
SYMBOLS - CONVENTIONS
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Figure 146
Typical Conventions
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Surface texture shown in micrometres
Surface texture shown in roughness numbers
Machining symbol
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When there is just a single number on the symbol, it shows the maximum degree of roughness that is acceptable. Sometimes, however, the surface texture is required between limits -- it must not be too rough or too smooth. This is shown by giving the maximum and minimum values:
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Surface Texture Surface texture is a measure of the smoothness of the surface finish. Where this is important, it will be specified on the drawing. When a particular quality of surface finish is required, it will be stated by numbers above the triangle. The drawing should specify which scale is being used -- centreline average or roughness number.
SYMBOLS - SURFACE TEXTURE
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Figure 147
Surface Texture Symbols
The machining symbol can be applied directly to the line representing the surface or it can be placed on a leader or extension line.
There are three scales commonly used for measuring surface texture. The smaller the number, the smoother the texture.
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Horizon
Right Vanishing Point
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A sketch is a loosely-structured hand-drawing graphically depicting an object or perhaps a proposed repair scheme. They are typically created without the benefit of drawing instruments. For this reason, an invaluable aid when creating a sketch is graph paper.
SKETCHES
Left Vanishing Point
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First Angle Projection The principle of first angle projection (European in origin) is shown opposite. Each view represents the side of the object remote from it in the adjacent view.
Orthographic Projection In order that drawings clearly show the designer’s requirements and provide the opportunity to show all dimensions, they are usually drawn in either first- or third-angle orthographic projection.
A perspective drawing shows an object in the way the human eye sees it. Lines used to construct this type of drawing meet up at a distant point - the vanishing point. Perspective drawings are seldom used in engineering, as they cannot accurately portray dimensions.
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PROJECTION
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C
Front View B
A
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Figure 148
Side View C
Plan A
Front View B
First Angle Projection
B
C
A
Symbol
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Side View C
B
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Third Angle Projection The principle of third angle projection (American in origin) is shown in Fig. 2. Each view represents the side of the object nearest to it in the adjacent view. The majority of drawings produced for aircraft purposes show the parts in third angle projection, but you may have occasion to use older drawings that were produced in first angle projection. Both systems show objects as they actually are, both in size (unless for convenience the drawing is scaled up or down) and shape, when viewed in the vertical and horizontal planes. The projection used for a drawing must be clearly stated and the appropriate international projection symbol must be placed in a prominent position on the drawing. Any views not complying with the projection stipulated, e.g. a view showing the true shape of an inclined face, as will be explained later, are generally marked with an arrow and suitably annotated.
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Figure 149
B
Plan A
Symbol
Side View C
Third Angle Projection
Front View B
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A
Front View B
Plan A
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GENERAL A sectional view shows the object drawn as if part of it is removed so that the interior shape is seen clearly. For this purpose the cutting plane selected must be clearly shown on one of the other views as shown below. As the example opposite shows, section lines are drawn equally spaced across the material which has been cut. These section lines, sometimes called hatching lines, are drawn at 45o to the axis of the section. if the drawing shows an assembly of parts, adjacent parts are hatched in different directions so as to distinguish the separate parts clearly. Nuts, bolts, rivets, shafts and ribs are not normally shown in longitudinal section.
SECTIONAL VIEWS
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Figure 150
Sectional View
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PART, HALF, AND STAGGERED SECTIONS If full sectioning is considered unnecessary, a part or half-section may be used, and staggered sections are often used to illustrate particular features. Examples of these are shown opposite.
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Figure 151
M7 MAINTENANCE PRACTICES ENGINEERING DRAWINGS, DIAGRAMS AND STANDARDS
PART, HALF AND STAGGERED SECTIONS
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AUXILIARY VIEWS None of the types of view mentioned will show the true shape of a surface if it is inclined to the normal planes of projection. The true shape of such a surface is shown by means of an auxiliary view drawn at right angles to the surface. An example of this is shown opposite.
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Figure 152
AUXILIARY VIEW
VIEW IN DIRECTION OF ARROW
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One of the methods shown below is usually used when dimensions are given from a common datum. Dimensions between holes are not often used since this allows a build up of tolerances. An alternative method, used with riveted joints, is to locate the end holes and add a note such as ’11 rivets equally spaced.’
DIMENSIONING FROM A COMMON DATUM
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20
75
DIMENSIONING FROM A COMMON DATUM
55
35
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20
Figure 153
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A general tolerance is usually given for all dimensions on a drawing and is stated in a printed box on the drawing. When the general tolerance is not appropriate, an individual tolerance may be given to a dimension. As shown opposite, tolerances may be expressed by:-S quoting the upper and lower limits, or by S quoting the nominal dimension and the limits of tolerance above and below that dimension.
DIMENSIONAL TOLERANCES
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Figure 154
Dimensional Tolerances
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GENERAL The blueprint system is used by the engineer to communicate his ideas to the various people who buy the raw material, plan the manufacturing sequences, build the parts and finally buy the product. Manufacturing. Planning, and Quality Control personnel will find that most of their contact with the blueprint system will be with engineering and tooling drawings. The purpose of this training section is to familiarize individuals from these and other areas with the engineering production drawing, procedures and specifications most commonly used in the fabrication, assembly and installation of the components that make up today’s modern aircraft and vehicles. Drawings used in the design, construction and maintenance of engineering projects are called ”production drawings”. Drawings used in the design, construction and maintenance of the jigs, tools and checking fixtures that are held in the building of an engineering project are called ”tool drawings”. Blueprints are simply copies of engineering drawings. Many ”blueprints” are not blue at all, but black lines on white, blue lines on white or even brown lines on white. ”Blueprint” has come to mean almost any colour of drawing reproduced on paper. Blueprints reproduced on metal or Mylar film are also available.
BLUEPRINT READING FUNDAMENTALS
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Figure 155
Detail Drawing 1
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Drawings used In the detailing or fabrication of single parts are called ”detail” drawings. Sometimes these drawings may be called ”fab” (for fabrication) drawings. Detail drawings do not put parts together. Most detail drawings are easily recognized by their titles. If the word ”assembly” or ”Installation” does not appear in the title, the drawing Is a detail drawing. An inseparable assembly delineates items or parts separately fabricated and permanently joined together, such as welded or riveted parts not subject to disassembly. The size of the drawing gives no indication of the drawing type. Some detail drawings are small, whereas others are large. The size of the drawing Is governed only by the size of the part or parts being detailed. S Remember: detail drawings do not ordinarily show location, position or fastening method. They will occasIonally show where a fastener will eventually be installed, but they do not show the fastener itself. Detail drawings are designed primarily to give instruction for fabrication personnel and provide only information used to make a part, since the assembly and installation information is of little value in fabrication work. Detail information indudes: S Size and shape description S Material and heat treatment requirements S Protective finish Instruction (painting, plating, etc.) S Machine finish if required (surface smoothness for metal) S Part numbering and marking instructions -- the next higher drawing number (here the part will be used). The engineer may not issue a separate detail drawing for each individual part. Frequently, several parts are detailed on one detail drawing, or some parts are detailed on assembly or installation drawings.
DETAIL DRAWINGS
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Figure 156
Detail Drawing 2
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NOTE: SOME OF THIS INFORMATION IS FOUND IN THE PARTS LIST. In addition, an assembly drawing may provide detail fabrication information about some or all the parts from which it is made. Thus, many are actually combination detail/assembly drawings. These are called assembly drawings even though they are not strictly assembly. Many assembly drawings contain some detail fabrication information. Bear In mind that there is a great difference between ”detailing” a part and merely ”showing” a part. To show a part requires only that the outline of the part, or a symbol of some sort, be pictured. Detailing a part requires a complete picture description. If a part is detailed on an assembly drawing, the assembly drawing completely describes that part. But a part can be shown on an assembly drawing by means of a symbol, incomplete picture, or even by location only, with no picture actually shown. Remember: A part that is detailed on one drawing can be shown on many drawings but cannot be detailed on another drawing. We see, then, that fabrication personnel are often required to work from the assembly drawings and that assemblers often find detail Information on their drawings.
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The engineer may not issue a separate assembly drawing for each assembly. Some assembly drawings tell how to built several different assemblies. Also, some assemblies are built from information on installation drawings. Most assembly drawings are recognized by their drawing titles, which must contain the word assembly” or ”assemblies”. The word ”assembly” is defined as follows: ”An assembly Is a multiple--piece item that can be disassembled into its component parts or units without destruction; it does not independently of Itself perform or fulfil a specific complete function but is essential for the completeness or proper operation of a more complex Item of equipment with which it is mechanically combined”.
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An assembly may comprise of only two parts or it may comprise many, depending on the judgment of the designer. In some cases, a large assembly may comprise several small assemblies fastened together. Information about how to locate the parts In reference to each other (not In reference to the entire airplane or vehIcle) and about how to fasten them together is called ”assembly Information”. The primary function of the assembly drawing is to show the relationship of two or more parts and subordinate assemblies, or a group of assemblies to form an assembly of a higher order. An assembly drawing must provide five items of information: S A list of required component parts and process specifications S Location dimensions (showing exactly how parts fit together) S Fastening methods S A part number for the finished assembly S The next higher drawing number (where the assembly will be used).
ASSEMBLY DRAWINGS
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Screw
Faucet Body
Upper Gasket Seat
Figure 157
Handle
Assembly Drawing
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Valve See Detail A
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NOTE: SOME OF THIS INFORMATION IS FOUND IN THE PARTS LIST. Note that the Items listed above are almost identical to those listed for assembly drawings. The major difference between the two lies in the interpretation of the word ”location”. Assembly drawings give locations of parts only as they pertain to each other; InstallatIon drawings give position within the aircraft or vehicle structure. Installation drawings are similar to assembly drawings in that the two are often combined. Actually, most of the Installation drawings are combination assembly/installation drawings. The drawing name describes the final operation performed. Detailed information about some or all of the assembly or installation components may also be given on the Installation drawing. Thus, many of the Installation drawings are actually combination detail assembly/installation drawings. They, too, are named by the final operation performed by the Installation. The word ”installation” appears In the title of all installation drawings
Installation drawings are designed to describe exactly where on the airplane or vehicle, or in a portion of the airplane or vehicle, certain parts or assemblies are to be permanently affixed. Installation drawings must provide the following information: S A list of required component parts and process specifications S Location dimensions (in reference to the entire airplane or vehicle) S Fastening methods S A part number for the finished installation (tabulation) S The next higher drawing number (used on drawing number).
INSTALLATION DRAWINGS
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Figure 158
Installation Drawing
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Illustrated parts lists often make use of exploded--view drawings to show every part that is in an assembly. All of the parts are in their relative position, but are expanded outward, so that each part can be identified by its physical appearance or by its name. It can also be identified by a reference number that is coded to the parts list.
EXPLODED-- VIEW DRAWING
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Figure 159
Exploded - View Drawing
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A schematic drawing does not show an exact image of an object; it is used to illustrate a principle of operation. It does, however, indicate where objects are located in relation to each other in a system and (if applicable) direction of fluid flow. Schematic drawings are ideal for trouble-shooting.
SCHEMATIC DRAWING
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Figure 160
Schematic Drawing
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Wiring diagrams indicate such things as size of wire and type of terminals to be used for a particular application. Several types of wiring diagram exist; some show only one circuit whilst others portray several circuits within a system. They also normally identify each component by both its part number and serial number. More detailed diagrams show wire connections at splices or the arrangement of parts. Like schematic diagrams, wiring diagrams do not show an exact image of a circuit; it is used to illustrate a principle of operation and also wire sizes. It does, however, indicate where objects are located in relation to each other in a circuit. Wiring drawings are ideal for trouble-shooting.
ELECTRICAL WIRING DIAGRAM
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Figure 161
Wiring Diagram
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CD--ROM With the development of compact discs and their incorporation into computers, it was a logical step to store electronic copies of drawings onto CD--ROMs. Now a complete aircraft’s drawings could be stored on perhaps 10 CDs; quite a difference to the small building necessary for it’s equivalent paper copies. Designers can distribute their drawings (and any amendments) to customers via this cheap medium. Doubtless as their use becomes more common, DVDs (with their superior storage capacity) will become the preferred option over CDs.
Computer Aided Design (CAD) The advent of computers resulted in engineering drawing software development; computer aided design, or CAD. Aircraft and their component parts could now be designed on a medium that did not have the problem of physical storage space for the finished drawings; they could be held digitally on magnetic media. Amendments to drawings was a formality and hard--copies could be produced via a printer linked to the computer.
Microfilm Instead of copies of each drawing being mounted in its own individual aperture card, hundreds could be stored onto a photographic film (microfilm). As with the aperture card, this microfilm could be loaded into a reader for ease of viewing and, if necessary, printing of hard--copies.
Aperture Cards One method used to reduce drawings’ physical size (and thus storage space) was to photograph them and mount the resultant slide onto a card. This card could be loaded into a viewer for ease of reading and a hard--copy subsequently printed off if necessary.
Introduction Engineering drawings have historically been created on paper at 1:1 scale and stored in cabinet drawers sufficiently large enough to contain them unfolded. This poses problems of storage space. A modern large aircraft has thousands of drawings; if paper copies of drawings were stored at their original scale, a small building would be needed for all the drawing cabinets.
DRAWING STORAGE
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Drawing Storage Methods
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Figure 162
Drawing Cabinet
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Microfilm Reader
Aperture Cards
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M 7.6 FITS AND CLEARANCES
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D = 25
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- 0,004 lower Dimension Upper Limit = 25 mm + 0,009 mm = 25,009 mm Tolerance = 25,009 mm 24,996 mm = 0,013 mm Lower Limit = 25 mm - 0,004 mm = 24,996 mm or 0,009 mm - (- 0,004 mm) = 0,009 mm + 0,004 mm = 0,013 mm Actual Size says the size the finished work piece actually is.
Example: Nominal Size
DIMENSIONS Dimensions are the ideal measurements for parts. Upper Limit is the largest measurement that will be accepted in production. You can calculate it with the help of the nominal size and the upper off size: In case c: upper limit = 30 mm - 0.04 mm = 29.96 mm Lower Limit is the lowest tolerable measurement and can be calculated using the nominal size and the lower off size: case c: lower limit= 30 mm - 0.06 mm = 29.94 mm + 0,009 upper Dimension
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A fit defines how tight or loose two joined parts fit. In single part production, those parts which are to be joined are usually fitted individually. In mass production this procedure would be uneconomical. It is essential that the work pieces can be assembled and if required changed without rework, regardless where and by whom they are manufactured. This interchange is only possible when there are uniform regulations (standards) for fits. This is why manufacturers’ fit standards were developed initially, then DIN fit standards for Germany and finally international fit standards ISO (International Organization for Standardisation). Shaft According to fit standardization a shaft is every rounded part that is fitted into a bore, regardless if otherwise called a peg, an axle, a bolt a pin etc. Nominal Size is the measurement which is calculated in the draft and used in the drawing. In the illustration below for example it is represented by the measurements 40,20 and 30. Tolerances In production the nominal size can never be exactly adhered to. A certain deviation has to be accepted. The tolerance defines which difference (measured in mm or in) is acceptable between the largest and smallest size. Reference Line At this line the deviation from the nominal size is zero. The off size 0 is not entered into the drawing unless misinterpretation could result.
SYSTEMS OF FITS
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Nominal Size
Upper Deviation Lower
Tolerance
Lower Limit
Reference Line
a b
Fits and Clearances - Fundamentals
Deviation
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Figure 163
Upper Limit
Nominal Size
Upper Deviation Lower
Tolerance
Lower Limit Upper Limit
40
-0.08 -0.03
20
+/-0.35
c -0.04
30
-0.06
d
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INTERFERENCE FIT In case of interference fit the hole is smaller than the item being fitted (for example in the case of a bearing bushing and its housing).
TRANSITION FIT In the case of transition fit, play or interference can occur between the parts, depending on the size of their actual sizes. The tolerances of bore and shaft overlap.
CLEARANCE FIT In cases of clearance fit you will always have some play after assembly, eg in bearings.
KINDS OF FIT According to their purpose the work pieces to be fitted are made with a different play or interference. This is why we distinguish between several kinds of fit.
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CLEARANCE FIT
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Figure 164
Basic Types Of Fit
Can be clearance or interference
TRANSITION FIT
CLEARANCE (space between hole and shaft)
A force is required to push the shaft through the hole
NO CLEARANCE
INTERFERENCE FIT
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INTERFERENCE The difference in diameter of the shaft and the bore is called interference if the diameter of the shaft is bigger than the diameter of the bore. Because of the tolerances of the shaft and the bore you get a maximum interference and a lower limit (maximum play)
CLEARANCE Play is the difference in diameter of the bore and the shaft, provided that the diameter of the bore is bigger than the diameter of the respective shaft. Because the shaft and the bore have to be subjected to a tolerance, in case of a larger quantity the parts usually have different play. You will get the largest play, if a shaft with the lower limit is fitted into a bore with high limit. The lowest play will result from a combination of a lower limit bore and a high limit shaft.
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Bore Tolerance
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Clearance
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Minimium Clearance Shaft Tolerance
Maximum Clearance
Figure 165
Interference
Clearance Fit
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Bore Tolerance
Minimum Interference
Maximum Interference
Shaft Tolerance
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UNIT-SHAFT SYSTEM When using the unit-shaft system, all shafts are manufactured with an H-tolerance (regardless of the required fit). The high limit of every shaft reaches the reference line and is identical with the nominal size. The lower size of the shaft is the nominal size minus the tolerance. The unit-shaft system is used for parts of transmissions, lifting equipment, textile machines and in precision mechanics.
UNIT-BORE SYSTEM When using the unit-bore system, all bores are manufactured with an H-tolerance (regardless of the required fit). The lower limit of every bore reaches the reference line and is identical with the nominal size. The high limit is the nominal size plus the tolerance. The unit-bore system is used for parts of machine tools, engines, motor cars, railroads and airplanes.
FIT SYSTEMS In order to maintain the different kinds of fit during manufacturing, you can either use the unit-bore system or the unit-shaft system.
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Nominal Size
Reference Line
Nominal Size
Reference Line
Transition Fit
Types Of Fit
Unit Shaft System
Transition Fit
Unit Bore System
Figure 166
Clearance Fit
Clearance Fit
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Shaft Tolerance
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Hole Tolerance
Interference Fit
Interference Fit
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Holes For: standard and oversize dia solid rivets standard and oversize dia blind rivets standard dia blind rivets (NAS54212 & NAS54213) standard dia Cherry-Buck titanium solid rivets standard and oversize dia blind bolts standard dia threaded pins and bolts (transition fit) 1st oversize dia threaded pins and bolts (transition fit) 2nd oversize dia threaded pins and bolts (transition fit) standard dia threaded pins and bolts (clearance fit) oversize dia threaded pins and bolts (clearance fit) standard dia threaded pins and bolts (transition fit close tol.) 1st & 2nd o’size threaded pins and bolts (transition fit close tol.) standard dia threaded pins (interference fit) 1st & 2nd o’size dia threaded pins (interference fit) standard dia special clearance fit bolts (tension) 1st & 2nd o’size dia special clearance fit bolts (tension)
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Table 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
The following tables are extracted from a typical aircraft Structural Repair Manual (in this case an Airbus A340--200/300). They give the permitted tolerances for holes for fasteners, depending on the type of fastener and kind of fit, as follows.
FASTENERS - HOLE AND DRILL DATA - METALLIC STRUCTURE
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Figure 167
Extracts From Airbus SRM - 1
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Figure 168
Extracts From Airbus SRM - 2
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Figure 169
Extracts From Airbus SRM - 3
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Extracts From Airbus SRM - 4
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Extracts From Airbus SRM - 5
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Extracts From Airbus SRM - 6
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Extracts From Airbus SRM - 7
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Extracts From Airbus SRM - 8
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Figure 175
Extracts From Airbus SRM - 9
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Figure 176
Extracts From Airbus SRM - 10
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Figure 177
Extracts From Airbus SRM - 11
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Figure 178
Extracts From Airbus SRM - 12
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Figure 179
Extracts From Airbus SRM - 13
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Figure 180
Extracts From Airbus SRM - 14
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A300 Outer Airbrake Attachments This is an example from the Maintenance Manual of wear limits.
WEAR LIMITS
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Page: 355
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Outer Airbrakes - Wear Limits (A300)
AIRBRAKE No 1
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Figure 181
HINGE AND JACK RIB
CENTRE HINGE BRACKET
AIRBRAKE No 2
M7 MAINTENANCE PRACTICES FITS AND CLEARANCES
Page: 356
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A300 Twist Check This is an example from the Maintenance Manual of twist limits. S Record height of the points of fuselage horizontal datum using the two sight tubes placed on either side of the fuselage. S Z variations of the fuselage horizontal datum points indicate fuselage twist. NOTE :The values in the table are actual measurements recorded on aircraft at zero flight hours and must only be used as guidelines for alignment checks. Deviation from the values and tolerances given does not automatically mean that the aircraft is not serviceable.
TWIST LIMITS
M7 MAINTENANCE PRACTICES FITS AND CLEARANCES
Page: 357
M7.6 (Cat A)
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Definition of Datum Axes
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Figure 182
Twist Check
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Alignment and Fuselage Twist Check
Page: 358
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Checking Method Engine crankshaft runout is checked with a DTI by assembling the instrument onto a stand and positioning it onto a smooth part of the crankshaft. A preload is then applied to the DTI by pressing it against the shaft so that the pointer deflects by a few thousandths of an inch. The DTI is then zeroed and, as the crankshaft is turned, the DTI will indicate the amount of deviation in both directions.
Dial Test Indicator (DTI) Dial test indicators are precision measuring instruments that can be used to determine the amount of movement between certain engine and airframe parts. They may also be used to determine and out-of-round condition on a shaft or the plane of rotation of a disk.
STANDARD METHODS FOR CHECKING SHAFTS & BEARINGS
M7 MAINTENANCE PRACTICES FITS AND CLEARANCES
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Figure 183
Using Dial Test Indicators
Dial test indicators are used to check shafts for out-of-round and for bends. They are also useful for checking backlash in gears and for measuring axle end play.
M7 MAINTENANCE PRACTICES FITS AND CLEARANCES
Page: 360
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ATA 20
CONNECTORS
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M7.7 ELECTRICAL CABLES AND CONNECTORS
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Electrical circuits are protected from excess current and overheating by circuit breakers.
These precautions apply to low voltage and high voltage equipment. Where electrical shock and burns are concerned, it is the current that does the damage, not the voltage.
When preparing to work on de--energized electrical circuits ensure that: -- the external power switch is off. -- the battery is disconnected. -- red safety tags are fitted.
If it is necessary to work on energised circuits or on live electrical equipment, always use adequate protective materials and extreme care.
Electrical equipment should never be operated in areas where explosive vapors are present or suspected, unless the equipment is explosion proof and designed specifically for use in such areas.
As well as the ever present danger of being caught or struck by moving parts, electrical equipment also presents the dangers of electric shock, burns, fire and explosion.
Note:These safety precautions are of a general nature and apply to all aircraft types.
SAFETY PRECAUTIONS ON AIRCRAFT
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R
Disconnect Battery
Battery
Remove External Power Plug
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Figure 184
R
to aircraft
Safety precautions
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This distance may be reduced to 15mm (0.59 in) for lines that do not carry flammable liquids i.e.: hot air, static air etc.
from lines carrying flammable liquids such as fuel, hydraulic oil, oxygen etc.
3 Wire bundles must run above or alongside piping at least 50mm (1.9 inch)
Carbon arc tracking -- installation precautions The installation segregation rules must be observed in order to limit the possibility of damage and interaction between routes. The electrical cables, connectors and the boxes and panels which accommodate them must be protected against water contamination.
must be protected against chafing by ensuring that there is no contact between the wire bundles and mechanical cables, metal tubes, or structural components.
2 Ensure that no mechanical stretch is present on the wire. Wire bundles
and groups which may include a variety of different wire types. i.e.: single, shielded, multicore etc. Individual groups must be spot tied and when these groups are bundled together the spot ties must not be removed. No plastic ties are allowed in unpressurised areas.
1 For ease of installation and maintenance, wires are arranged into bundles
ESPM 20--33--41
SWPM 20--10--11
ESPM 20-33--10
Each time a connector is disconnected and reconnected: -- Do a visual check of the connector locking. -- Carry out a functional test of the related systems.
Page: 365
-- The wire is correctly, mechanically connected to the plug or terminal block/ module as applicable. For wires with crimp contacts this involves pulling the wire lightly. -- A continuity check and functional test of the related system is carried out.
General Inspections and checks (ESPM 20--52--10) Each time a wire is added, repaired, or reconnected, ensure that:
c) For single co--ax cables and wire bundles with co--ax cable attached, the minimum bend radius is 10 times the outside diameter of the co--ax cable.
b) The smallest bend radius for wire bundles is 6 times the outside diameter.
a) The minimum bend radius for single wires or cables is 3 times the outside diameter. The best and preferred value is 10 times the outside diameter.
possible in order to prevent cracks occurring in the insulation.
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4 The bend radius of wire bundles must be extended to the maximum
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Design of the wiring installation shall conform to the following precedence : S 1st-- Flight safety. S 2nd-- Ease of maintenance , removal and replacement of parts. S 3rd-- Cost effective aircraft production and repair.
GENERAL NOTES
CONNECTORS
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FRAME
GROUP SPOT TIES
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Figure 185
WIRE BUNDLE
General Installation
4
3
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WIRE BUNDLE
NOT CLAMPED ON HYDRAULIC, HOT AIR, FUEL OR OXYGEN TUBES
Page: 366
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A wire bundle that has an overbraid shield installed must be identified with a W number: -- Within 18 inches of all connectors -- Within 18 inches of all shield terminations -- At branches -- Every six feet. The shield must have the same temperature grade as the wire bundle.
5 General Conditions for Overbraid Shields (SWPM 20--25--11)
4 Conduits provide mechanical protection for wire bundles. Wires must not be tied or fastened together inside conduit or insulating sleeving. A draw wire must be installed for ease of modification. Oil or temperature resistant Scotch Electrical Tape as applicable must be used for abrasion protection and secured with flat waxed binding tape at both ends. Make a drainage hole after installation is complete and the lowest point is firmly established.
3 When a wire bundle is dressed downward to a connector, terminal block etc. a drip loop must be installed to prevent fluid contamination.
required to facilitate connector removal. This is particularly important if the connector is at the rear of an indicator which has to be pulled forward through a panel for disconnection.
2 When wiring is terminated at a connector, a minimum length of slack is
Coaxial cables must be installed separately from other wire bundles and with the maximum possible bend radius (10 times the outside diameter).
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Aircraft that are fitted with AP wires at manufacture must be repaired and modified with the same wire type or suitable alternative as listed in the Wiring Diagrams Manual.
Aircraft that are not fitted with AP wires and cables at manufacture must not have AP wires and cables fitted during repair or modification. Only the wire and cable types in the Wiring Diagrams Manual are authorised for use. If however, you find AP wires already installed, they can be left on the aircraft.
Aromatic polyimide (AP) wires and cables
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1 Wire bundles in the fuselage or wing must be clamped at every frame.
GENERAL NOTES (CONTINUED)
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5
Drainage hole 1/8 in diameter at lowest point
General installation (cont)
WIRE BUNDLE LENGTH SUFFICIENT
4
3
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Figure 186
WIRE BUNDLE CLAMPED AT EVERY FRAME
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
DRIP LOOP
WIRE BUNDLE
Page: 368
PLUG
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Note: Aromatic polyimide wires must be wrapped with insulation tape prior to clamping to prevent damage to the insulation.
Metal clamps can be used in any area of the aircraft provided that they are fitted with the appropriate insulation material.
Plastic clamps must not be used in areas where the temperature exceeds 250 _ F (121_ C).
Page: 369
(SWPM 20--10--12, ESPM 20--33--42)
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Wire harnesses are: -- Permitted to move in a longitudinal direction in a loop clamp -- Permitted to turn clockwise and counterclockwise in a loop clamp -- Not permitted to move or turn in a block clamp.
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Cable Clamps Primary support of the wiring installation is provided by plastic and metal cable clamps spaced at intervals not exceeding 24 inches. Clamps must fit properly to prevent damage to the wire insulation. No wires must be pinched in the clamp Rubber fillers can be used to improve the fit of a clamp but must not be used with co--axial cables.
WIRE AND CABLE SUPPORT
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Folding Wing Clamp
b) Metal clamp
a) Plastic Clamp
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M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Insulation
Figure 187
High Vibration Clamp
Clamps
CORRECT
Cut
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Rubber Fillers not for Coax-Cables
Filler Plugs
INCORRECT
0.10 in to 0.25 in
Page: 370
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3 Wires passing through a bulkhead must be supported at each hole by a cable clamp. If the clearance between the wires and the edge of the hole is less than 1/4 inch, a suitable grommet must be fitted.
Bundles must be routed and clamped to preclude chafing against the edges of equipment and structure. Where physical separation of at least 3/8 inch cannot be maintained, the edges must be fitted with suitable protection strips or grommets. Shielded cables must have an external insulating cover.
2
No washers, ties, tapes, etc. are allowed inside fuel tanks as they could become loose and clog filters.
1 If nylon clamps use a spacer, a washer must be fitted.
Clamps ( continued)
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Frame
Structure
Figure 188
Wire Bundle
Clamps
3
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Grommet
Clearance
Less Than 6mm
Page: 372
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It is also desirable that the back of the clamp rest against a structural member where practicable.
Clamp installation Clamps should be installed in the prefferred attitude, as shown below. The mounting screw should be above the wire bundle.
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Figure 189
Clamp Installation
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Preffered installation
Less desireable installation
Page: 374
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SWPM 20--10--11
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Note: do not use ties inside fuel tanks
S In normal applications, ties are required at approximately 8 in intervals. In high vibration areas the interval must be decreased to 2 in maximum.
S It is not necessary to install the new wires under existing ties. They must however, be installed within all the support clamps of the parent bundle and not on the outside of plastic ties or other hard material.
S Tie additional wires to the exterior of the bundle with ties between clamps at approximately one foot intervals.
S Do not place ties on wire bundles located inside conduits.
When tying, observe the following precautions: S Tie bundles tightly enough to prevent slipping, but not so tight that the cord cuts into or deforms the insulation. This is especially applicable to coax cable, which has a soft dielectric in between the inner and outer conductor.
Cotton, nylon or fiberglass lacing cord is used for tying. Cotton cord must be of the waxed type to ensure moisture and fungus resistance.
This ensures that the wires are neatly secured in groups and bundles to aid compliance with wire bundle separation requirements and to avoid possible damage from chafing or equipment operation.
Wire groups and bundles are tied to provide ease of installation, maintenance and inspection.
WIRE BUNDLE TIES
CONNECTORS
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Figure 190
BUNDLE TIES
Bundle Ties
GROUP BUNDLE TIES
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3
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SWPM 20--10--11
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ESPM 20--33--41
The three illustrations below show some correct and incorrect methods for wire bundle tying in a high vibration area.
1
Examples of tying bundles
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Incorrect
Correct
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Figure 191
2 in max
Incorrect
Correct
Scotch Tape
Wire bundle tying examples
3
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SWPM 20--10--11
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ESPM 20--25--51 and 20--33--44
Plastic wire ties must not be used in the following applications: S On wire bundles with wire larger than10 AWG S On wire bundles installed in unpressurised areas S On wire bundles installed in high vibration areas S On wire bundles in high temperature areas (higher than 85_ C (185 _F)) S On wire bundles designated ’Fly By Wire’ on engineering drawings S With aromatic polyimide wires unless the bundle is wrapped with tape. S With coaxial cables
Plastic wire ties or straps Plastic wire ties or straps are available in a variety of different sizes, they must only be installed with the correct tool. The tool for installing tywraps NSA935401 is shown below.
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Figure 192
OF THE TIE WRAP
Plastic wire ties
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SWPM 20--10--13 ESPM 20--53--2X --The cable shield must be fully closed and electrically continuous around the repaired area.
--The repair technique adopted is dependant upon the type of damage.
Repair of shielded cables
--It may be necessary to change the wire routing to prevent the damage reoccurring.
--Wire lengths subject to heat damage must be replaced wherever the outside insulation has changed colour. The replacement wire length must be the same type and size.
Repair of single conductor wires --Wires with chafed or broken insulation must repaired by splicing if possible.
--An engine harness wire or a fire warning wire repaired with a splice is considered an acceptable temporary repair and must be replaced when the next maintenance is carried out.
--In a wire bundle where all the wires require repair by splicing, the splices must be staggered. This means that the diameter of the wire bundle is increased symmetrically, slowly and continuously so that no splices overlap.
--The maximum number of splices allowed in a wire is 3. This does not include production splices identified in wiring diagrams.
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ESPM 20--24--01
Page: 381
b) In high temperature areas, only grade D insulation tape must be used.
a) Outside the pressurised area, only aircraft fluid resistant tape must be used
Notes:
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Conditions for repair with a splice --Replacement of the damaged wire is is always the preferred option over the repair of the wire with a splice.
REPAIR OF WIRE AND CABLE
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Existing wire
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Crimped splice
Repair of wire and cable
Staggered splice locations
Figure 193
Crimped splice
New wire
Wire tape wrapped to protect against chafing and abrasion
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Existing wire
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--Splices must not be installed: S inside metal or flexible tubes S within 12 in of a termination device S under clamps or other wire bundle support S inside fuel tanks S in wire harnesses that are frequently bent (hinged panels or doors)
--Splices must not be used to salvage scrap lengths of wire.
Splice restrictions --There shall not normally be more than two splices in any wire segment.
CONNECTORS
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There is a wide range of techniques available for creating electrical connections, almost all of which involve crimping tools. This section will cover those which are most commonplace.
High quality electrical connections can be consistently achieved by using the correct terminations, with the correct tool for the job, accompanied by the correct wire preparation technique.
A high proportion of aircraft faults are due to poor connections caused by normal wear and tear. It is therefore vitally important that tradesmen with a responsibility for creating new connections do not build in any further, future problems.
The importance of high quality, low resistance connections in electrical and electronic systems can not be over emphasised.
INTRODUCTION
ELECTRICAL CONNECTIONS
CONNECTORS
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It is strictly forbidden to use the Superchamp for crimping!
Wire strippers The graphic below illustrates two common hand wire strippers.The stripmaster on the left is a versatile automatic hand stripper. The gripper holds the wire in position and one light squeeze of the handle severs and strips the insulation slug up to 7/8 in. The Superchamp tool can also be used for wire stripping.
In all cases, the greatest care should be exercised during wire stripping as any decrease in overall conductor diameter will incrrease the resistance of the joint.
The first and one of the most important operations required before any wire can be assembled to connectors, terminals, splices, etc. is the stripping and preparation of the wire. The following general precautions are to be observed when stripping any type of wire: S When using any type of wire stripper, hold the wire so that it is perpendicular to the cutting blades. S Adjust automatic stripping tools carefully; follow the manufacturers instructions to avoid nicking, cutting, or otherwise damaging strands. S When using hand plier strippers, the removal of lengths of insulation longer than 3/4 inch is easier to accomplish in two or more steps. S Use stripping blades appropriate to the insulation thickness. S When stripping coaxial cables with a knife, scratch the soft outer insulation carefully without damaging the underlying shield. S After stripping ensure that the insulation is cut cleanly with no frayed or ragged edges. S Make sure all insulation is removed from the stripped area .Some wire types are supplied with a transparent layer of insulation between the conductor and the primary insulation which can be missed during stripping. S Where necessary, re-twist strands to restore natural lay and tightness.
STRIPPING WIRE AND CABLE
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SWPM 20--00--15 ESPM 20--25--11
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BLADE or DIE
Numbering system on blades:
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Figure 194
Wire stripping
Blades for thick wire Insulation
(BLADES)
CHANGEABLE
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Blades for thin wire insulation
Page: 388
Wire Stripping Allowed
Crimping Forbidden
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ESPM 20--25--41; 20--53--51 SWPM 20--61--17; 20--63--00
Apr 2004
Rear release contact removal 1. Slip the white removal tool around the wire of the contact to be extracted. 2. Slide the tool along the wire into the insulator until it buts against the shoulder of contact. 3. Remove wire and tool rearwards.
Rear release contact insertion 1. Press the wire into the coloured slot with the thumb. 2. Under this pressure the slot will open to accept the wire. 3. Hold the connector in one hand and insert the contact into its cavity,pushing with tool perpendicular to the insulator face. When contact is in place a metallic click is audible. 4. Remove tool to the rear. Check that contact is firmly in position by pulling gently.
The graphic below illustrates the rear release system
All connector contacts are inserted from the rear. There are however two general systems for removal of connector contacts: The Rear release system and The Front release system
General Great care must be taken when inserting and removing connector contacts. The internal mechanism of the connector is easily damaged and can only be repaired by connector replacement.
CONTACT INSERT & REMOVAL
CONNECTOR TOOLS
CONNECTORS
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Figure 195
Rear release removal
Rear release contacts
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Rear release insertion
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
REMOVAL
Incorrectly Locked Contact
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SWPM 20--61--11; 20--61--16 (-19)
--Align tool squarely with insert face. --Push tool squarely into insert hole until it butts against insert face. --Holding the tool firmly, advance the slider knob so that the contact is ejected from its seated position. --The contact may than be pulled free of the grommet by hand.
Front release contact removal
--Slip insertion tool over the wire and butt it against the contact shoulder --Align tool and contact axially with the grommet --Guide contact carefully through grommet hole, pushing tool axially to grommet --Remove tool and check that contact is firmly in position by pulling gently.
Front release contact insertion
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Incorrect
Figure 196
Correct
TOOL
TUBE
CONTACT
FRONT RELEASE CONTACT REMOVAL
PUS H SLIDER FrontHAN release contacts DLE
WIRE
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FRONT RELEASE CONTACT INSERTION
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Apr 2004
--Rotate the multi--locator turret to the correct colour coded position.and push in to engage. --Select the appropriate wire size on the selector knob. --The crimping operation is completed as for MS3191--1.
Prior to crimping with this tool the following set up must be carried out:
This tool is similar in construction to the MS3191--1. The major difference is that it has one, multiple locator turret secured by two allen screws instead of three separate turrets.
Crimping tool MS3191--4
Page: 393
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ESPM 20--25--21
All crimping tools must be inspected and certified at a regular interval.
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Crimping tool MS3191--1 Crimping tool MS 3191--1 is a precision tool used to crimp standard contacts size 12, 16 and 20. Each contact size uses its own colour coded locator which must be inserted prior to crimping. The locator is needed to position the contact in the correct position for crimping so that no additional setting of the tool is required. The handle ratchet mechanism will open automatically after crimping when the handle is fully depressed.
CONNECTOR CONTACT CRIMPING-TOOL
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COLOR CODE DATAPLATE
YELLOW
BLUE
RED
CODE
COLOUR
LOCATOR
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
P/N
CONTACT SIZE
Figure 197
WIRE SIZE
Crimping Tool
Positioners R, B, Y
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ESPM 20--25--11 (-21) SWPM 20--61--00
Apr 2004
Assembling the back-shell With the contacts inserted, screw the back-shell onto the body of the connector. Tighten the back-shell nut using the plug wrench as necessary until it is mechanically tight.
Filler wires can be used to increase conductor outside diameter for larger contact sizes. Cut filler wires flush with rear of crimp barrel taking care not to damage the strands of the primary wire.
The illustration below shows some correct and incorrect examples of connector contact crimping. In all cases, ensure that: -- All the strands of the conductor are in the crimp barrel -- The end of each conductor is bottomed in the crimp barrel -- The conductors are visible in the inspection hole.
In almost all cases the wire insulation must have no direct contact with the end of the crimp barrel. Adherence to the correct stripping length dimensions will ensure that a small gap exists to provide flexibility.
The pictures below give a general idea of the wire stripping lengths required for connector contacts. For exact stripping lengths appropriate to each contact type, refer to the SWPM and ESPM.
As previously specified, for a good crimping result it is first necessary to prepare the wire correctly.
CRIMPING OF CONTACTS
CONNECTORS
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PLUG WRENCH
FILLER WIRE
PRIMARY WIRE
CORRECT
INCORRECT
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Clamp
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Connector
INSPECTION HOLE
Figure 198
FILLER WIRE CUT HERE
LOCATION OF FILLER STRANDS
Crimping check
Plastic Inserts
WIRE NOT BOTTOMED
AND CONTACT
WIRE BOTTOMED
SPACE BETWEEN INSULATION AND CONTACT
NO SPACE BETWEEN INSULATION
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The solder sleeve slides into position over the wire with the solder band centered over the stripped area of outer insulation and the shield ground wire. It should be noted that one end of the solder sleeve is slightly wider than the other. The wider end should be toward the shield ground wire.
The heatshrink gun is then used to shrink the sleeve into position and enable the solder in the sleeve to run. This creates an electrical connection between the ground wire and the cable shield.
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Post shrinking inspection: --Solder sleeves exhibiting dark areas or slight discoloration are acceptable, provided that the solder can be inspected and the solder sleeve is not ruptured or split. --Ensure that the seal rings have melted and provide an environmental seal. --Ensure that the solder band has melted fully around the pigtail and shield braid.
The shield ground wire and the cable shield must be stripped to the correct dimensions.
1
The solder sleeve is equipped with two sealing rings on the inner ends of the sleeve and a band of solder in the center.
The solder sleeve pigtail is the most common method for attaching a shield ground wire to shielded cables.
SOLDER SLEEVE PIGTAIL
CONNECTORS
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Solder Ring
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Correct stripping of shield and ground wire insulation
Seal Ring
Solder sleeve pigtail
CONNECTORS
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Figure 199
Seal Ring
Solder sleeve pigtails
3
2
1
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Heat Shrink Gun
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ESPM 20--48--00
RED
BLUE
YELLOW
22--18
16--14
12--10
Apr 2004
YELLOW
26--24
2,7 - 6,6 mm2
1,0 - 2,6 mm2
0,25 - 1,6 mm2
0,1 - 0,4 mm2
WIRE SIZE COLOR CODE
colour coded to identify the wire sizes that can be crimped in each lug or splice.
In addition, pre-insulated terminal lugs contain an insulation grip ( a metal reinforcing sleeve) beneath the insulation for extra grip on the wire insulation. Pre-insulated terminals accommodate more than one wire size, the insulation is
In this range of terminals and splices, the insulation is part of the terminal and splice construction. It extends beyond its barrel so that it will cover a portion of the wire insulation, making the use of an insulating sleeve unnecessary.
Ring tongue type terminals are used for most aircraft applications.
PRE INSULATED DIAMOND GRIP (PIDG) TERMINALS AND SPLICES
CONNECTORS
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SERRATIONS
COLOR CODED
INSULATION GRIP
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Figure 200
FUNNEL RAMP ENTRY
PIDG Terminals & Splices
WIRE STRANDS
COPPER SLEEVE
TINPLATED COPPER TONGUE
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INSULATION
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The following video gives a general overview of the crimping process for AMP PIDG terminals and splices.
Video: Introduction to Crimping Basics
After the crimping operation is complete, the quality check described below must be carried out.
The crimp tool has an Insulation grip position selector which sets the insulation crimp, appropriate to the insulation thickness.
The picture below illustrates a typical AMP crimping tool for PIDG terminals and splices.
CRIMPING OF PIDG TERMINALS AND SPLICES
CONNECTORS
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COLOR CODE INFO TABLE
LOCATOR
INSULATION CRIMP SETTING
RATCHET
AMP ’T’ HEAD CRIMPING TOOL
CONNECTORS
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Figure 201
Crimping of Terminals
a) strands must be visible b) dots must be present
QUALITY CHECK:
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SWPM 20--30--12
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The illustration shows the unsealed variant. Sealed, moisture resistant versions are also available which are supplied with a crimp ferrule and insulating sleeve.
After crimping, the closed end splices may be placed side by side in an upright position within 30 degrees of eachother.
The correct splice size is determined by the cross sectional area of the all the wires to be inserted.
The length of the breakout is limited to 21/2 in max, unless further limited by the bundle assembly drawing.
The use of closed end splices is possible where it is specified in the aircraft wiring diagram manual chapter 91.
CLOSED END SPLICES
CONNECTORS
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Crimp Tool
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M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
1
1
1
Figure 202
Closed End Splice
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45_ to
45_ to
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Note: Only one un-stripped wire allowed per end cap.
A typical wire cap crimping tool is shown below.
-Stowed wires must be visible at the outside of the bundle.
-After installation of wire caps, the spare wires must be wrapped, tied and stowed near the unused termination.
The same conditions apply for spare wire caps that were previously described for dead ending of wires, i.e. -Spare wire caps must be installed within four to six inches of connectors.
SPARE WIRE CAPS
CONNECTORS
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Figure 203
Crimping spare wire caps
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Correct colour codes.
Wire size corresponds to marking on terminal.
Conductor strands visible.
Conductor strands visible in window.
Insulation correctly crimped.
Both ends crimped on upper side.
3
4
5
6
7
8
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Crimping in center of crimp abrrel.
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1
CORRECT
CRIMPING-INSPECTIONS
CONNECTORS
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Wire not properly inserted or incorrect stripping length
Wire incorrectly inserted in the terminal.
Number of dots incorrect.
Wire size does not correspond to marking on terminal..
Conductor strands not visible.
No strands visible in window.
Insulation crimping incorrect .
Both ends not crimped on upper side.
1 2 3 4 5 6 7 8
INCORRECT
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POSITIONED
SPLICE INCORRECTLY
CORRECT
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Figure 204
PRINTED HERE
MAX WIRE SIZE
TOOL TURNED 180 DEGREES
Crimping inspections
PRINTED HERE
MAX WIRE SIZE
INCORRECT
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SWPM 20--30--00
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Note: The maximum number of terminals on one stud is four.
Terminal strips Install terminal strips as indicated on the illustration below.
TERMINAL STRIPS, BLOCKS & MODULES
CONNECTORS
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Figure 205
Terminal strips
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C--Type - One Block 8 sockets, one bus, eight common contacts.
D--Type - One Block 8 sockets, two busses, four contacts per bus.
A--Type - One block, 8 sockets, four busses, two contacts per bus.
Different bussing configurations are also possible:
In some installations the contacts are labeled A, B, C and D.
The two upper contacts are both labeled - A. The two lower contacts are both labeled - X.
The completed block installation below right details how connections are presented on wiring diagrams.
The installation method above right is an alternate method for inserting or changing a single block on the track.
The left lower picture shows the proper method for installing the terminal blocks on the tracks.
The left upper picture on the following page illustrates the different terminal block configurations which are available.
TERMINAL BLOCKS
CONNECTORS
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“A”
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
“D”
Figure 206
“C”
Terminal blocks
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eg.:
eg.:
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Terminal block contact replacement The process for contact preparation, insertion and extraction is described on the illustration below.
CONNECTORS
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Figure 207
Crimping terminal block contacts
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ESPM 20--44--51
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Typical module configuration and identification is illustrated below.
--All unused positions can be environmentally sealed by the insertion of a seal plug.
--Many different combinations are used with different wire size contacts in the same module.
--Each module has its own number mounted on top of the module.
The main differences between terminal modules and blocks are:
Terminal modules Terminal modules can accomodate either ten or twenty one contacts.
CONNECTORS
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PRINTED ON WIRING
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M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Figure 208
VIEW ON BLOCK
G H J K
B C D E
Terminal modules
BLOCK NUMBER
BLOCK NUMBER
F
A
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TYPICAL COMBINATIONS
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ESPM 20--51--22 SWPM 20--20--00
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The illustrations below show some typical bonding techniques.
1. To minimise radio and radar interference. 2. To eliminate fire hazard by preventing a spark between two metallic components at different potentials. 3. To minimise the damage to the aircraft and its passengers from lightning strikes . 4. To provide a low resistance return path for single wire electrical systems. 5. To aid in the effectiveness of the shielding.
The reasons for bonding may be summed up as follows:
An aircraft can become highly charged with static electricity whilst in flight. Aircraft electrical bonding is the process of obtaining the necessary electrical conductivity between the component metallic parts of the aircraft. Bonding also provides the low resistance return path for single wire electrical systems. This low resistance return path also aids the effectiveness of shielding and provides a means of bringing the entire aircraft to the earth’s potential when it is on the ground.
BONDING
CONNECTORS
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M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Bonding
Tank
Bearing
Bonding
Structure
Figure 209
Bonding
Junction box
Structure
Anti- vib mounting
Bonding metal clamp
Bonding
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Bonding metal clamp
Black box mounting
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SWPM 20--20--00 ESPM 20--51--22
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The illustration below shows methods for measuring bonding resistance.
Values for bonding are detailed in the aircraft maintenance manual.
If this process is done correctly, measurements not higher than 0.025Ω can be obtained.
Measurement of bonding resistance To ensure a low resistance connection for bonding leads, non conducting paint and anodizing films must be removed from the surfaces to which the bonding terminals are to be attached.
BONDING RESISTANCE
CONNECTORS
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Figure 210
Bonding resistance measurement
Basic Structure
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Structural Interface
Ω
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Bonding
Test leads
Bonding Meter
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When installing grounds, the following conditions apply: -Grounds must be seperated; AC, DC and shields. -There must be no more than four terminals on one stud. -In fuel vapour area (see right) dual grounds must be installed.
Grounding points must be of sufficient dimensions in order to allow the required current flow, including fault current, without generating heat.
Grounding is the process of connecting these systems and the shields of shielded cables to the aircraft metallic structure at pre-designated points. Grounding must be effected with particular care by means of good quality contacts.
The aircraft metallic structure is used as a conductor for current returns for the single wire electrical systems.
GENERAL
GROUNDING
CONNECTORS
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
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Additional ground wire, same wire size or one size larger
1
TERMINALS
SAFETY NUT
Figure 211
SWPM 20--20--00
Grounds
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TYPICAL GROUND STUD IN FUEL VAPOUR AREAS
CONNECTORS
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TYPICAL COMMON GROUND
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ESPM 20--44--71
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NOTE: Exact values are given in the Aircraft Maintenance Manual
Instruments, computers etc.
5MΩ
200MΩ
Between terminals and grounds
C) Wires for other systems :
100MΩ
Between terminals
B) Wires without accessories terminals, plugs, contacts etc:
10MΩ
5MΩ
Galleys, lighting, service systems
Other service systems
2MΩ
Engine cowlings, landing gear, wheels, etc.:
A ) Wires for accessories:
Summary of British Civil Airworthiness Requirements Chap. EEL/4--1, Page 9.
General overview of insulation-resistance measurement values.
Insulation resistance testing should only be carried out on wires disconnected from their systems at both ends.
The usual test voltages are 250V or 500V.
The insulation resistance is measured between individual wires (wire to wire) and between individual wires and the aircraft structure (wire to ground).
Carry out tests prior to installation where possible.
INSULATION RESISTANCE MEASUREMENT
CONNECTORS
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M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Measurement of insulation resistance
MEASUREMENT OF INSULATION RESISTANCE WIRE TO GROUND ESPM 20--52--24
INSULATION ERROR
MEASUREMENT OF INSULATION RESISTANCE WIRE TO WIRE
INSULATION ERROR
INSULATION RESISTANCE MEASUREMENT
Figure 212
2
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Continuity testing must only be performed on circuits with no power applied.To use an ohmmeter or multimeter as a continuity tester it is necessary merely to contact the end terminals of the circuit being tested with the test probes of the meter.
Testing continuity is the process whereby an ohmmeter or multimeter is used to determine if a circuit has a complete (continuous) current path.
CONTINUITY TESTING
CONNECTORS
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Turn off power to the circuit
Apr 2004
Plug the black test lead into the COM input jack. Plug the red test lead into the ohms input jack
Select resistance
M7 MAINTENANCE PRACTICES M7.7 ELECTRICAL CABLES AND
Figure 213
Continuity testing
View reading
Connect the probe tips across the protion of the circuit to be measured
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ESPM 20--52--23
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The reflected pulse form will give an idea of the incident: -Any short will reflect a negative pulse (picture 2b). -Any open coax cable will reflect an positive pulse (picture 2c).
The TDR is sensitive to impedance changes. Problems in the cable will be detected and displayed as changes in impedance along the cable. These will be displayed as hills and valleys in the reflected pulse. The TDR is capable of finding shorts, opens, defect shield, foreign substances in the cable ( water, etc.), kinks and more.
Principle The TDR sends an electrical pulse down the coax cable and detects any reflections made by discontinuities.
General Time Domain Reflectometry (TDR ) is a measurement concept that is beginning to find great usefulness in the analysis of wideband systems.
COAX CABLE TESTING
CONNECTORS
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PICTURE 2
REFLECTED IMPULSES
PICTURE 1
ZV
Apr 2004
TESTED COAX CABLE ZM
IMPULSE GENERATOR
TIME DOMAIN REFLECTOMETER
CONNECTORS
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ZE
Figure 214
Z = TERMINATION RESISTOR
OSCILLOSCOPE
Coax Cable Testing
PICTURE 3
DENTED CABLE 4% IMPEDANCE CHANGE. IMPULSE IS OPPOSITE TO FRAYED CABLE
FRAYED CABLE 8% IMPEDANCE CHANGE, CORROSION MAY OCCUR LATER
TYPICAL CABLE PROBLEMS
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SHORTED CABLE SHORTED TO THE CENTER CONDUCTOR.THE IMPULSE IS OPPOSITE TO OPEN CABLE.
OPEN CABLE POSITIVE IMPULSE
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M7.8 RIVETING
M7 MAINTENANCE PRACTICES RIVETING
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Types There are essentially two types of rivet head; one that protrudes and one that sits flush with the material. These are known as universal and countersunk heads. The most common countersink angle is 100o.
Sizes The most common diameters of solid rivets fitted in aircraft are: S 3/32in (2.4mm) S 1/8in (3.2mm) S 5/32in (4.0mm) S 3/16in (4.8mm) Different lengths are available in 1/16“ increments.
Rivets A rivet is a metal pin with a formed head at one end; either protruding or countersunk. A hole is drilled through the parts to be joined, the rivet is inserted into the hole and the end opposite the head is hammered to hold the components together. As the rivet tail is hammered down, its cross-sectional area increases together with its bearing and shearing strengths (its resistance to the force of the components trying to slide apart). This process creates a union betwen the parts at least as strong as the individual parts. Because weight is an important factor when constructing aircraft, the solid-shank rivet is the most preferred method when joining metal parts together.
Joining Methods Modern materials, particularly composites, use adhesive to form a permanent bond. Traditionally, aluminium alloy (and other metal) parts are joined using rivets.
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Storage Time (Hours) 48 72 150 Infinite
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One further ’cook’ is permissable if time runs out, but then the rivets must be discarded.
Storage Temperature (oC) 0 -6 -15 -40
Heat Treatment D-, DD- and E-rivets are made from an alloy called duralumin and are very hard and brittle. Before fitment they are heated to approximately 4950c and held at the temperature for long enough that all rivets are completely heated through. The rivets are then quenched. This process produces a soft rivet that is designed to harden over a period of time. The hardening process can be speeded up by cold working the rivet. Rivetting provides just such a cold working process and rivets that are driven within 30 minutes of quench will change from soft and malleable to hard fasteners. If rivets are not to be used within the 30 minute post-quench period, they can be frozen to retard the natural age hardening process. freezer storage life depends on storage temperature:
Material Aircraft structure is made up of many materials, including steel and titanium. The designer must consider various factors (weight, heat, load etc) when deciding which material to use, only sacrificing weight when it is necessary. For its excellent strength-to-weight ratio, the most common material used in an aircraft structure is aluminium alloy. This section will concentrate on aluminium alloy solid rivets (as opposed to steel and titanium, which are rarely encountered). To prevent dissimilar metal corrosion and other stresses, rivets are composed of the same alloys as the structures they are joining together. As covered in Module 6, aluminium is alloyed with various other elements, depending on where it is fitted and what loads it is subjected to.
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Aircraft structure consists of various components manufactured separately and subsequently joined together.
INTRODUCTION
M7 MAINTENANCE PRACTICES RIVETING
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M7 MAINTENANCE PRACTICES RIVETING
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Aeronautical Material Specifications Air Force Navy Air Force Navy Design Aeronautical Standard American Standards Association American Society for Testing and Materials Military Standard Naval Aircraft Factory National Aerospace Standard Society of Automotive Engineers
99.00 % minimum aluminium Copper Manganese Silicon Magnesium Magnesium and Silicon Zinc Other elements Unused series
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Rivets also have a letter assignation which is commonly used for quick identification, as well as head markings.
1XXX 2XXX 3XXX 4XXX 5XXX 6XXX 7XXX 8XXX 9XXX
Wrought Alloys Alloy Number Major Identifying Elements
The aluminum industry uses a four--digit index system for the designation of its wrought and cast aluminum alloys, and this is carried across to rivet coding.
Abbreviations for Common Aircraft Hardware Standards/Specifications
AMS AN AND AS ASA ASTM MS NAF NAS SAE
M7 MAINTENANCE PRACTICES RIVETING
Shank Diameter
Figure 215
Solid Rivets
Length measurements correspond to grip length.
Shank Diameter
Countersink Angle (100o)
426 (Countersunk)
Length of Rivet
470 (Universal)
Rivet part numbers indicate head style, material and size.
5/16in Length
4/32in Diameter
2117T4 Alloy
Universal Head
Airforce Navy
AN 470 AD 4 - 5
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1.5D
2117 5056 AD B
1.5D
2017 2024 DD D
7050 E
2 raised Raised dashes cross Raised Raised Dimple dot ring
Page: 432
Hole is normally drilled 0.1mm larger in diameter than rivet shank diameter. When driven, rivet swells to diameter of hole. Exact dimensions are given in aircraft SRM.
.5D
1100 A
Plain
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Allowance The amount of protrusion of the rivet shank that is sufficient to form the shop head (’tail’).
Sphere of Influence The area of sheet metal over which a rivet will achieve a water-tight joint (typically 5D).
Spacing Spacing is the distance between fastener rows, taken from the hole centres. Use 4D as a rule of thumb.
Edge Margin Use 2 to 2.5 D as a rule of thumb.
Edge Distance The bolt and pin hole edge distance values are from the centre of one fastener hole to the nearest edge of the component. The edge distance values applicable to the protruding head fasteners for the wing structure are quoted in terms of the fastener nominal shank diameter ‘D’. For example, factor 2.0 x ‘D’ = edge distance . The edge distance values applicable to protruding and countersunk head fasteners are given in the repair instructions provided by the SRM.
Pitch The bolt and pin hole pitch values are from the centre of one fastener hole to the centre of the next fastener hole in a row and are quoted in terms of the fastener nominal shank diameter ‘D’. For example, factor 4.0 x ‘D’ = pitch. RD
P
SP EM
1.1D to 1.5D
0.5D
Allowance
0.6D to 0.75D
Fastener Pattern Terminology
1.3D to 1.5D
ST
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When a sheet metal repair is to be done, there are certain minimums that must be attained for rivet spacing, edge margin and fastener diameter. The fastener spacing and margin data applicable to metallic and composite structures are given in the Structural Repair Manual (SRM) Chapter 51.
Layout
RIVETED JOINTS
M7 MAINTENANCE PRACTICES RIVETING
Page: 433
1.6D to 1.7D
EM -- Edge Material RD -- Rivet Diameter SP -- Spacing ST -- Skin Thickness P -- Pitch
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Extract from Airbus SRM
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Figure 216
Fastener Edge Distance
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Extract from Boeing 737-- 300 SRM
Figure 217
M7 MAINTENANCE PRACTICES RIVETING
Dimensions for Driving Non-Fluid-Tight Solid Rivets (Boeing)
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Figure 218
Extract from Boeing 737-- 300 SRM
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Grip Ranges/Recommended Lengths: Standard Aluminium Alloy Rivets (Boeing)
M7 MAINTENANCE PRACTICES RIVETING
Page: 436
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Extract from Boeing 737-- 300 SRM
Figure 219
M7 MAINTENANCE PRACTICES RIVETING
Dimensions for Driving Non-Fluid-Tight Solid Rivets (Boeing)
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Extract from Boeing 737-- 300 SRM
Figure 220
M7 MAINTENANCE PRACTICES RIVETING
NACA Method BACD 2027 Type II Countersink Driven Head
Dimensions for Driving Fluid-Tight Solid Rivets (Boeing)
Driven Head
Drive to Fill Countersink
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Because the aircraft engineer will encounter both metric and Imperial units of measurement (particularly when carrying out structural repair work), a pocket-sized manual (such as the Zeus book) is an invaluable aid for quick conversion work.
UNITS OF MEASUREMENT
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Figure 221
Standard Drill Sizes & Decimal Equivalents
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Wing Structure Maximum rivet spacing of the wing structure is deemed to be 3.75D (solid rivet) or 4.5D (or 10t, whichever is smaller) for a Hi-Lok rivet.
Pressurised Fuselage To prevent skin plates buckling, the maximum permissable rivet spacing of a pressurised fuselage should be 6D or 18t (whichever is the smaller).
INTER-RIVET BUCKLING
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Figure 222
Fuel Tank Fastener Spacing
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Introduction If skin is too thin to cut-countersink, it is shaped (dented) to accept the head of a countersunk fastener by dimpling. There are three methods of dimpling. S Coin Dimpling. A male die fits through the rivet hole and the coining ram in the female exerts a controlled pressure on the underside of the hole whilst the male is forced into the upper side. The pressure on the dies forges the edges of the hole to exactly fit the shape of the dies. Coin dimpling gives the hole sharply-defined edges that closely resemble machine dimpling. The top and bottom of the dimple are formed to a 100o angle, enabling dimpled skins to be stacked (or ’nested’). S Radius Dimpling. The pilot on the male die passes through the hole in the material and presses into the female die. The dimple formed does not have parallel sides as the lower side has an angle greater than 100o, therefore these dimples cannot be nested. Radius dimpling equipment is smaller than that used for coin dimpling and can be used in locations too tight for coin dimpling. S Hot Dimpling. Magnesium and some of the harder aluminium alloys (such as 7075) cannot be successfully cold-dimpled, as the material is so brittle that cracks will form during the process. To prevent this cracking, the material is heated during the process. The equipment is similar to that used for coin or radius dimpling except that the dies are heated. The material is put in place and heat and pressure applied. The metal softens under the heat and the pressure then increased to form the dimple. The amount of heat and duration it is applied is carefully controlled to prevent the temper condition of the metal being destroyed.
DIMPLING
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Page: 443
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100o 100o 100o 100o
Female Die
Movable Coining Ram
Sharp Break
Coin Dimple
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Coin Dimpling
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Male Die
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Figure 223
Dimpling
Radius Dimpling
Setting Block
Pilot Tip
Punch
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Hot Dimpling Machine
Page: 444
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Gun Riveting The rivet gun, used with a back-up dolly (bucking bar), forms the upset head. This is known as reaction riveting. A correctly-shaped rivet set (rivet snap) is held in the gun and located on the manufactured head end of the rivet. At the same time the dolly is held against the end of the rivet to be upset. When the gun operates, the dolly reaction to the pneumatic hammering of the gun forms the upset head.
Riveting Methods For the installation of rivets, the following methods can be employed: S pneumatic rivet gun S hand hammering S continuous squeeze-riveting.
TOOLS USED FOR SOLID RIVETING
M7 MAINTENANCE PRACTICES RIVETING
Page: 445
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Adjusting of Force
WOODPLATE
SafetySpring
Rivetset
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Trigger
Figure 224
Rivet Guns
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Rivet Gun Capacity (Boeing -- assembler / installer manual)
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MAKE SURE THAT THE HAMMER BLOWS ARE HEAVY AND AS FEW AS POSSIBLE BECAUSE A LARGE NUMBER OF LIGHT BLOWS WORK-HARDEN THE RIVET. THIS CAN RESULT IN CRACKS IN THE UPSET HEAD. Make sure that the tools are sufficiently large to quickly form the upset head. The subsequent times for the formation of the upset head are recommended: S three or four seconds is the optimum time, S seven seconds is the maximum time. Hold the back-up dolly in position until the rivet is fully installed. Before you install rivets in the aircraft structure, make some test pieces to check the rivet and tool precision. These test pieces must be the same type of material and thickness as the parts to be riveted, and the rivets must be the same type of material, length and diameter as the rivets to be used. Visually check rivets before they are installed. If a rivet appears defective (eg deep scores or indication of wire drawing) reject it. Some apparent defects (eg isolated nicks, abrasions, die marks or fins) are acceptable up to a maximum depth of 0.10mm (0.004 in). Rivets made from 2017 and 2024 materials must be kept in a refrigerator after they have been heat-treated.
NOTE:
Hand Riveting Hand hammering (also known as ’percussion riveting’) is the basic method used to make the upset head of a rivet. For this method follow these steps: 1. Support the manufactured head with a correctly-shaped rivet set 2. Hold a dolly against the end of the rivet and hit it until the upset head has achieved the correct shape.
M7 MAINTENANCE PRACTICES RIVETING
Page: 447
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Rivet Set for Flush (Countersunk) Head
Rivet Set for Universal Head
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Figure 225
Rivet Sets
Curved Rivet Snap
Straight Rivet Snap
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Upset Rivet Set (for frame area)
Reworked Rivet Set (for stringer area)
Page: 448
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Squeeze Riveting The continuous squeeze method is the preferred method for riveting, but if this method is not available then pneumatic hammering is the next recommended method. The hand hammering method is used primarily for small repairs that include very few rivets. It can also be used if other methods are not available. A squeeze riveting tool makes the upset head of a rivet in a single continuous action. Tools to perform this are either hydraulically or pneumatically operated. Static and portable types of tools are available.
M7 MAINTENANCE PRACTICES RIVETING
Page: 449
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Guard
Trigger
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CP214 C Rivet Squeeze
CP351 C-Type Squeeze
CP351 Alligator-Type Squeeze
Trigger
M7 MAINTENANCE PRACTICES RIVETING
Die
Air Supply
Guard
Air Supply
Guard
Y
T
Rivet Squeezers
C. Installed Rivet
Figure 226
A
C
MS
With trigger pulled, add enough snap die length so the total distance between die faces (’C’ dimension) equals T + A
A. ’C’ Yoke Squeeze
G
X
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Y
X
X & Y - snap dies. If X & Y length must be adjusted, use a steel washer.
T - material thickness
MS - maximum stroke
G - steel washer (die length adjustment option)
C - T + A (opening left after full travel of piston)
A - desired rivet button thickness
With jaws closed so the die seats are parallel to each other (surfaces B & D) and jaw faces E & F form a straight line, add enough snap die length so that the ’C’ dimension equals T + A
B. Alligator Squeeze
D
B
G
C
Page: 450
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3/32 7/64 1/8 9/64 5/32 11/64 3/16 13/64 7/32 15/64 1/4 17/64
2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 6.0 6.4 6.8
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in
mm
Rivet Diameter
2.57 2.97 3.35 3.76 4.17 4.57 4.95 5.36 5.77 6.17 6.55 6.96
in
in 0.097 0.113 0.128 0.144 0.160 0.176 0.191 0.207 0.223 0.239 0.254 0.269
Minimum 2.46 2.85 3.25 3.66 4.06 4.47 4.85 5.26 5.66 6.07 6.45 6.83
mm
Hole Diameter
0.101 0.117 0.132 0.148 0.164 0.180 0.195 0.211 0.227 0.243 0.258 0.274
Maximum
mm
May 2004
Extract from Airbus SRM
Hole Diameter - Solid Rivets
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Replaceable Pilot-Pin
Countersink Bit
Stop
Typical Microstop Countersinking Tool
Adjuster
Page: 451
Flush Rivets The use of a countersunk fastener requires a countersunk recess in the surface of the material. The countersunk recess receives the head of the fastener and therefore gives a smooth surface. The tools, used to produce the countersunk recess, are of various types: S a countersink bit with an integral pilot pin, a cutting edge to produce the required internal corner radius and an adapter for use with a drilling machine, S a countersink bit with a replaceable pilot pin and an adapter for use with a drilling machine, S an adjustable countersink tool with an integral pilot pin and a cutting edge to produce the required internal corner radius, S an adjustable countersink tool with a replaceable pilot pin. NOTE: The diameter of the pilot pin must fit the diameter of the fastener hole. The diameter of the countersink bit must be larger than the maximum diameter of the required countersunk recess. Before countersinking, observe the minimum part thickness (see table opposite).
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Introduction The dimensions of a fastener hole have an important relation to the strength of the fastened joint. CLearance fit, transition fit or interference fit fasteners are used depending on the loading. Deburr the hole using a suitable deburring tool. NOTE: A twist--drill is not permitted for this step.
HOLE PREPARATION
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Extract from Airbus SRM
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Figure 227
Minimum Part Thickness for 100o Countersinking
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Flush Rivets (Cont’d) CAUTION: CARE SHOULD BE TAKEN THROUGHOUT THIS PROCEDURE TO ENSURE THAT THE COUNTERSINK PRODUCED IS NOT TO DEEP. Obtain a piece of scrap metal to use as a test piece, similar in type and thickness to the material that is to be used for the repair . Also obtain a fastener of the same type and diameter as the ones to be installed. Drill several holes to the required diameter in the test piece. Adjust the micro stop on the countersinking tool to give a minimum countersink. Make a countersink on the test piece. Gradually increase the amount of countersink by adjusting the micro stop until the required depth is obtained. Check the depth with the correct fastener. Refer to Chapter 51--10--00 of the SRM for the required Aerodynamic Smoothness for the type of fastener. When the required depth of countersink has been obtained, check that the remaining parallel portion (excluding the de--burred area) of the hole is at least 0.2 mm (0.008 in.) long. Complete the test by fully installing a fastener in the test piece and check for correctness. NOTE: When using a micro-adjustable countersinking tool, ensure that the stop on the tool does not rotate when countersinking. Rotation of the stop can cause damage to the surface of the material around the countersink. NOTE: If a large number of countersinks are to be made, the adjustment of the tool must be checked from time to time. To achieve adequate seating of the fastener, the edge of the countersunk recess/hole must be chamfered (see opposite). Some countersinking tools produce a chamfer (radius) in a one--step operation with the countersinking. If the produced radius has the correct dimension for the required fastener (refer to Chapter 51--44--11), no further chamfering is necessary.
HOLE PREPARATION (CONT’D)
M7 MAINTENANCE PRACTICES RIVETING
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Figure 228
Underhead Radius/Chamfer Limits
Applicable to 100o countersink-head fasteners.
Applicable to plain holes for protruding-head fasteners.
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NOTE: Install the rivets before the pot-life of the sealant or jointing compound ends. 6. Make sure that the contact surfaces of the parts are fully together and that there are no gaps between them. Gaps will prevent the correct forming of the rivet and reduce the joint strength. 7. Align the holes as necessary and attach the parts together temporarily. Take care not to cause damage to the local area with tools. 8. Put the rivet fully in the hole. For this operation make sure that the parts are correctly supported where necessary. 9. Form the upset head. To do this, use one of the methods given in the general section. Hold the tools perpendicular to the surfaces and do not compress the rivet too much. If the upset head is over-compressed, it is possible for the material to crack.
NOTE: If necessary, the rivet can be shortened to the required length. This does not apply to titanium rivets. 3. Get the correct rivet set and back--up dolly for the rivet type and dimensions. 4. Make sure that the hole, and if applicable, the countersunk portion is in a satisfactory condition. This includes clean and free from burrs. 5. Clean the parts as necessary. Apply sealant or jointing compound if it is called for in the related repair drawing, assembly drawing or is normally used in the area concerned.
Select the required rivet. If, for any reason, the dimensions of the required rivet are not known, proceed as follows: 1. Accurately measure the diameter of the hole. If the diameter of the hole is within the tolerances for a standard rivet (Refer to SRM 51--40--40), select a rivet of this diameter. If the diameter of the hole is not within the tolerances, increase the diameter of the hole to suit an oversize rivet if applicable, or the next standard size. 2. To find the required rivet length, accurately measure the total thickness of the materials to be joined. Refer to rivet length data tables to find the correct length that is relevant to the rivet diameter found above.
INSTALLATION PROCEDURE
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Figure 229
Bucking Bars - Details
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Aerodynamic Smoothness Aircraft designers insist that certain areas of the aircraft surface must be aerodynamically smooth. It may also be necessary to fit a panel or other component over countersunk fasteners, in which case it is important that there is no protrusion of the fasteners that can result in damage to the component being fitted. To achieve a flush finish to a countersunk rivet, a microshaver is used. The tool is micro--adjustable and should be set up on a piece of spare metal. The cutter’s height is set so that, upon lowering to the metal surface, no material is removed. Check the setting by increasing the cutter’s height one step at a time until material is removed, then backing off again. The aircraft SRM must be consulted before shaving rivets.
General Inspect rivets after they have been installed. This is necessary to make sure that the joint is tight, and that the rivets are fully seated and correctly formed. Make sure that the adjacent area has no damage or distortion. The acceptance limits given in the following tables are applicable to those rivets that become part of the structural strength after installation. For example, rivets that fasten skin or formed and extruded sections. A large number of cracks found in a high percentage of installed rivets indicates that the rivets have not been correctly heat-treated. It can also mean that the installation time allowed for heat--treated rivets has been exceeded. It is necessary to scrap and replace all of these rivets (including those which are not used) from the batch concerned, or have them heat--treated again. Deformation or buckling of the plating is only permitted within the limits given in SRM Chapter 51--10--30. This type of damage is a result of: S too much tool pressure S rivets expanded between the sheets S trapped foreign material. Make sure that the head of a countersunk rivet is level with or slightly above the surface of the material. Refer to SRM Chapter 51 for the rivet head protrusion limits.
INSPECTION AND PERMITTED LIMITS
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Microshaver
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Figure 230
Upset Rivet Dimension (Airbus)
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Figure 231
MALFORMATION
PERMITTED IF IN UPSET HEAD HEIGHT LIMITS
NOT PERMITTED (RIVET SHANK VISIBLE)
Formed Head Defects and Limits (Airbus) 1
PERMITTED IF IN UPSET HEAD HEIGHT LIMITS
PERMITTED
ECCENTRICITY
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MAX 5% OF TOTAL PLATE THICKNESS
M7 MAINTENANCE PRACTICES RIVETING
Figure 232
MAX 30% OF CIRCUMFERENCE
Formed Head Defects and Limits (Airbus) 2
RAD 0.3mm (O.012in)
TOOL IMPACT DAMAGE
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NOTE: Cracks in the heads of titanium and monel rivets are not permitted. Lack of head/material abutment (seating) is permitted within the limits given in the SRM.
Acceptable Limits Ovality of the upset head is permitted if the dimensions are within the upset diameter limits. These limits, together with the applicable rivet material, are given in the following tables. Eccentricity of the upset head is permitted if the rivet shank cannot be seen. Malformation of the upset head is permitted if the shape is within the dimension limits given in upset rivet dimension tables. Tool impact damage around the two heads is permitted within the limits given in sketch. Cracks in the upset head of aluminium alloy 2017 and 2024 rivets are permitted within the limits given in the table/sketch. Cracks in the upset head of other aluminium alloy rivets are not permitted. Cracks in the structure material under either head are not permitted.
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Figure 233
Acceptable Limits for Cracks (Airbus)
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Extract from Boeing 737-- 300 SRM
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✔
✘ Vertical cracks due to overheating during heat-treatment is unsatisfactory.
Cracks Analysis: Shop Head (Boeing)
Vertical cracks due to laps in the material is satisfactory.
✔
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Figure 234
Vertical cracks in CRES alloy, nickel-copper alloy and titanium rivets.
M7 MAINTENANCE PRACTICES RIVETING
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Extract from Boeing 737-- 300 SRM
M7 MAINTENANCE PRACTICES RIVETING
Figure 235
Cracks Analysis: Non-Fluid-Tight Rivets (Boeing)
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Extract from Boeing 737-- 300 SRM
M7 MAINTENANCE PRACTICES RIVETING
Figure 236
Cracks Analysis: Fluid-Tight Rivets (Boeing)
Unsatisfactory - displaced metal or cracks with an intersection on the flat surface.
✘
Satisfactory - no displaced metal or gaps.
✔
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Gap Inspection Shim
Exposed area of countersink is not permitted.
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✔
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Shim
Shim is wedged and does not move freely in this direction.
No measurable gap is allowed.
W = 0.5 in nominal.
Length is optional.
M7 MAINTENANCE PRACTICES RIVETING
Shim
✘
60% of the head must not have a gap that a shim can find.
✘
Protruding Head Gap Inspection Method
Shim
Shim touches the shank or head-to-shank fillet and moves freely in this direction.
Shim
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Extract from Boeing 737-- 300 SRM
Shim
Shim stops suddenly when it touches the shank and is not wedged.
Gap Inspection Method for Flush-Head Non-Fluid-Tight Rivets
✔
Shim is wedged. A light force is necessary to remove the shim.
✔
Gap Analysis: Rivet Heads/Tails (Boeing)
Shim
the shank or in this direction.
Figure 237
✘
Shim touches moves freely
No measurable gap is allowed.
0.002 in nominal.
R = 0.25 in nominal.
Shim is wedged and does not move freely in this direction.
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Method 1. If the head type is protruding and its centre cannot be accurately established (covered in sealant or paint), file it slightly to produce a flat. 2. Centre-punch the head as a guide for the drill-bit. NB Alternatively, to prevent undue stress by centre-punching, position the drill-bit and turn the chuck by hand to create a start for the drill-bit. 3. Carefully drill (using a bit of the same size as the rivet shank diameter) just to the bottom of the rivet head. To prevent damage to the structure, do NOT be tempted to chisel off the head. Provided you have drilled centrally, the head will part easily during the last part of this operation. 4. Support the structure on the reverse side. Using a parallel pin-punch of the rivet shank diameter, drift out the rivet tail.
Safety S As with all operations involving drills, wear eye protection. S Check whether there is anything behind the rivet (wire loom, pipes etc). S Warn anyone in the vicinity you are about to drill. S Rivet removal generates a lot of debris. Prevent, as far as possible, this entering cavities. S Be scrupulous in cleaning your work area.
Caution Fastener holes are one of the main sources of structural fatigue and failure. It is vital that they are not damaged during the rivet removal process. You cannot automatically increase a rivet size if holes are enlarged. In certain areas, the SRM cannot authorise this and the aircraft’s design department must be approached for a concession, incurring delays and expense. Fasteners will not form correctly in enlarged holes, thus reducing their effectiveness. Therefore, great care should be taken during this operation.
SOLID RIVET REMOVAL
M7 MAINTENANCE PRACTICES RIVETING
Page: 467
M7.8 (Cat B1)
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Extract from Boeing 737-- 300 SRM
Step 4
Drift Punch
Figure 238
Solid Rivet Removal
Step 3
Drift Punch
Support the
Back-Up Support
NOTE: start the drill by hand. Use a drill-bit 1/32“ diameter smaller than the rivet shank.
Drill through the head of the rivet so that the drill does not damage the skin or cut the sides of the rivet hole.
Page: 468
M7.8 (Cat B1)
IR PART 66
CAUTION: to prevent cracked dimples or damaged understructure when removing rivets from dimpled holes, drill a hole into the rivet shank before driving it out.
Drill
Drive out the rivet shank with a drift punch and hammer. Use a block of wood or a bucking bar as a back-up support.
Step 5
Back-Up Support Centre-punch the centre of the manufactured head. For both flush and non-flush rivets use a block of wood or a bucking bar as a back-up support.
Step 2
Centre Punch
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Insert a drift punch into the hole drilled in the rivet and tilt the punch to break off the rivet head.
Manufactured head
File a flat area on the manufactured head with a file.
Step 1
File
M7 MAINTENANCE PRACTICES RIVETING
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Installation Tube assemblies are laid in a manner so that they can yield along their length if there is movement and vibration, so that there is no significant additional stress on the fittings. This is achieved by providing suitable bends in the tubing. For the same reason the vibration of the line itself must also be reduced to a minimum. This is achieved by clamping at short regular intervals. The proximity of lines to each other must also be observed to prevent them damaging each other through contact.
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CAUTION:
Page: 470
PRESSURE TESTING IS NORMALLY THE RESPONSIBILITY OF SPECIALISTS. A PIPE THAT BURSTS UNDER PRESSURE CAN CAUSE SERIOUS OR EVEN FATAL INJURIES.
Cleaning and Pressure-Testing A manufactured pipe assembly must be cleaned out internally with compressed air (blown from both directions alternately) and then proof-tested (normally at 1 1/2 times working pressure) by capping one end.
The smallest permitted bend radius for the tube assembly is dependent on the tube material, the wall thickness and the outer diameter. At the same time, the lines must be able to connect to the connections exactly matching the axis and be free of tension so that they maintain the necessary seal over longer operating periods.
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General A tube assembly consists of the tube and both tube fittings. Tube assemblies are differentiated according to their use as low, medium and high pressure tube assemblies. Extruded tube material of various non-corrosive steels, aluminium and titanium alloys is available. Their dimensions are determined by the ”nominal diameter”, the ”external diameter” and the ”wall thickness”. The higher the quality of material that is selected for a line, the easier it is to achieve the same operational pressure with reduction of the wall thickness and thus less flow resistance due to the larger inner diameter. Steel lines are increasingly being used as pressure lines, even if this could be accomplished with aluminium lines. The reason for this is the greater operating safety and the longer life expectancy. S At pressures of over 1500 PSI (105 bar) we speak of high pressure lines, S under 1500 PSI (105 bar) medium pressure lines S suction and return lines we speak of low pressure lines. Medium and low pressure lines are preferably made of aluminium alloys for weight-saving. Lines in the engine area, where there is danger of fire, and in the landing gear area, where there is danger of being hit by stones, must principally be made of steel. Titanium lines are still the exception; they can be used due to reasons of weight or as ”flexible metal pipes” instead of hoses.
TUBES AND PIPES / TUBE ASSEMBLIES
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M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 239
✘
Bulkhead
Correct Tube Alignment
✔
Bulkhead Fitting
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WHEN INSTALLING A BONDED CLAMP, ENSURE ANY PAINT OR ANODIZING IS REMOVED FROM THE LINE WHERE THE CLAMP IS FITTED FOR ELECTRICAL CONTINUITY.
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CAUTION:
Bonded Clamps A bonded clamp is used to secure metal fuel, oil or hydraulic lines. It has an electrical lead connected to the aircraft structure to ground the line.
Support Clamps Support clamps are used to secure fluid lines to the aircraft structure or to assemblies in the engine nacelle. In addition to providing support, these clamps prevent chafing and reduce stress. The two clamps most commonly-encountered are the rubber cushioned clamp and the plain clamp. The rubber cushioned clamp secures lines which are subject to vibration. It reduces the transmission of vibrations to the line and prevents chafing. In areas subject to contamination by fuel or hydraulic fluid, cushioned clamps utilizing Teflon are used, which are highly-resistant to deterioration.
Introduction For appearance’ sake and ease of attachment, all fluid lines should follow structural members of the aircraft and be secured with appropriate clamps; ie all fuel lines must be bonded to the structure with integrally bonded line support clamps. It is important that no fluid line be allowed to chafe against any control cable or aircraft structure, electrical wiring bundles or conduit-carrying electrical wires. Furthermore, you should avoid routing fluid lines through passenger compartments. If, however, this is unavoidable, it must be supported and protected against damage and installed in such a way that it cannot be used as a hand-hold.
CLAMPS
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Figure 240
Clamp Types
Cushioned Clamp
Plain Clamp
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DO NOT OVER-TIGHTEN THE JOINT IN ATTEMPTING TO CURE A LEAK. THIS MAY RESULT IN FAILURE OF A COMPONENT.
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CAUTION:
Leak Inspection If a leak is apparent from a correctly-tightened joint, it should be dismantled and mating surfaces thoroughly inspected for debris or damage.
Flare Angle Aircraft flared fittings have a standard flare angle of 37o and are not interchangeable with vehicle-type flares, which are 45o.
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Dimensions See next page.
Page: 474
Single Flare A single flare is formed with either an impact-type flaring tool or one having a flaring cone with a rolling action. S Impact-Type This method involves the tubing being clamped in flaring blocks (the ’grip die’) whilst a plunger is driven into the end of the tube using light hammer blows whilst rotating the plunger. S Roll-Type This is the preferred method, involving an entirely self-contained unit producing a good flare. The tube is clamped and the flaring cone is turned into the tube end, expanding the flare until it reaches the edges of the die. No hammering is required.
Types of Flare There are two types of flare used in aircraft tubing systems: S Single Flare S Double Flare.
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Introduction With a flare-type fitting a special tool is required to make the flare. By tightening the union nut, a sleeve is pulled against a conical fitting, whereby the tube is pressed between the fitting and the sleeve. The close fit between the inside of the flared tube and the flare cone of the fitting provides the actual seal, therefore surfaces must be scrupulously clean and free of cracks, scratches and nicks etc. The sleeve provides added strength and suports the tube to prevent vibration concentrating on the flare. This fitting is relatively complicated to manufacture, but has proved its worth for use in engines because it is relatively vibration-resistant.
FLARE-TYPE FITTING
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Nut
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 241
Tube
Sleeve
Steel Pilots
Grip Die
Roll-Type Flaring Tool
Impact-Type Flaring Tool
Tubing
Yoke
Single Flare Fittings and Tools
Grip Die
Flaring Tool Plunger
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Tubing
Page: 475
SIDE VIEW
TOP VIEW
Grip Die shown in vice
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Flare
Minimum Flare
Flare
Maximum Flare
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Sleeve External Diameter
Sleeve External Diameter
B
37o
1
3/4
5/8
1/2
3/8
5/16
1/4
3/16
1/8
Tube OD (in)
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Dimensions Single flares must be manufactured to certain tolerances to ensure a strong, leak-free joint.
Single Flare (Cont’d)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
1.187
0.937
0.781
0.656
0.484
0.421
0.359
0.302
0.200
+0.000 -0.015
Page: 476
0.093
0.078
+0.000 -0.010
0.062
+0.000 -0.010
0.062
0.046
+0.000 -0.010
+0.000 -0.010
0.032
0.032
+0.000 -0.010 +0.000 -0.010
0.032
0.032
B Radius +0.010 (in)
+0.000 -0.010
+0.000 -0.010
Steel or Aluminium Alloy Tubing (in)
External Sleeve Diameter
Dimensions for Single-Flare Tubing
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AN939 Elbow
AN832 Union
AN833 Elbow
AN941 Elbow
AN824 Tee
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Common Aircraft Pipe Fittings
AN938 Tee
AN827 Cross
AN821 Elbow
Figure 242
AN916 Elbow
AN917 Tee
AN914 Elbow
AN912 Bushing
AC AN Feature Angle 35o 37o ✘ ✔ Recess Coarser Threads Finer Grey Blue or or Colour yellow black Longer Body Length Shorter
AC
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Flared fitting part numbers are either ’AN’ or ’MS’. Some older types (’AC’) still exist. It is important to be aware of this and note that there are a number of physical differences that mean they are NOT interchangeable.
AN
Tapered Pipe Thread Fittings
AN915 Elbow
AN913 Plug
AN910 Coupling AN911 Nipple
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Body Length
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Procedure S The tubing is inserted into the flaring die to a depth determined by the stop-pin and then clamped. S The upsetting tool is inserted and, with as few blows as possible, the initila upset is formed. S The upsetting tool is then substituted for the flaring tool and then hammered to form the double flare.
Double Flare Soft aluminium tubing with an outside diameter of 3/8 in or smaller can be double-flared to provide a stronger connection. A double flare is smoother and more concentric than a single flare and thus provides a better seal. It is also more durable and resistant to the shearing effect of torque.
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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3. Complete flare
2. Form initial upset
1. Position tubing against stop
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 243
Double Flare
0.032 0.032 0.032 0.032 0.046
B Radius +0.010
Dimensions for Double-Flare Tubing
0.224 0.302 0.359 0.421 0.484
1/8 3/16 1/4 5/16 3/8
Tube Size
37o
A Diameter +0.010 -0.010
B
A
Tube Size (Nominal External Diameter)
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Tools Care must be taken to ensure that the correct tool is used for bending tubes. The choice of tool depends on the diameter of the tube. The swivel handle of the larger tube benders has an angled slot. The whole swivel handle can slide outwards so that the tube can be laid in the guide groove. After this the swivel handle is pushed down again and the tube clamp is placed around the tube. The left side of the swivel handle is now on the zero marking of the scale. It is recommended to lightly lubricate the tube at the bend point before bending. To bend the tube, secure the tube bender with the form wheel handle in a vice. The tube is bent by pulling both levers together. With steel tubes, you usually arc the bend a little further than the marking on the scale, as the tube springs back a little after bending. This is hardly ever the case with light metal tubes. After bending, the swivel handle is pushed up over the slot again, the tube clamp moved back and the tube removed.
BENDING TUBES
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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Figure 244
Tube Bender
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Tools (cont.) Tube benders for small tube diameters have no slot in the swivel handle; instead, it is on the reverse side of the lug. When you open the swivel handle with the lug, the tube can easily be inserted here too. With both of these tube benders you are not limited to making 180° bends, you can also make any open bend to your required angle.
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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Figure 245
Tube Clamp
Tube Bender
Swivel Handle
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Form Wheel Handle
Tube 3/8“
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Form Wheel
Guide
Page: 483
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With an open tube bend, you must ensure that the dimension (X) from the middle of the tube to the middle of the tube at the desired point is marked exactly. First, you bend the right bend to 90°, during which the tube must be held so that the right marking on the tube covers the marking (L) on the form wheel (see Figure 207). Then the tube is pushed further right in the tube bender until the left marking on the tube covers the marking (R) on the form wheel. Now the second 90° bend can be made.
TUBE BENDING COMING UP TO REQUESTED DIMENSIONS
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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X
Figure 246
Bending
Form Wheel Handle
Tube 3/8“
Tube Clamp
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Swivel Handle
Form Wheel
Guide
Page: 485
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It is often very advantageous to fabricate the tube bend at the installation site to ensure that it fits exactly. Tube bends must be made in such a way that the tubes can be installed totally tension free with no tension in the clamps and fittings. Some tube assemblies must be bent with very exact measurements due to the aircraft structure. This is especially so at an S--bend that must run parallel, i.e. it is very important at an offset. First, the required measurement (Y) from tube centre to tube centre must be determined. You can bend any offset angle. The tube is bent as widely as possible when a small offset is required. In the example below, a 15, 30 or 45° angle is shown on the left. Sharper angles of 60, 75 or 90° can easily be used with a larger (Y) measurement. The manufacturer recommends that a 45° angle is bent where possible. A table, which you can use to determine the correct dimension of an offset, comes with the tube bender.
TUBE BENDING COMING UP TO REQUESTED DIMENSIONS (CONT.)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 247
Tube Bending to Requested Dimension 1
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To carry out an offset, you can draw and bend at a certain point according to the table, using the measurements (X) and (Y). As an example, assume a required dimension of 2 ½ inches at Y (from tube centre to tube centre). If we want to bend an offset of 45° we see from the table, under the offset angle 45°, that the measurement (Y) of 2 ½ inches is next to the measurement (X) of 3 17/32 inches.
TUBE BENDING COMING UP TO REQUESTED DIMENSIONS (CONT.)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 248
Tube Bending to Requested Dimension 2
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On the straight tube, the measurement (X) is therefore drawn at 3 17/32 inches at the place where the offset shall be. To bend a 45° offset, we must bring the first marking on the tube to the 45° line marking on the tube bender (shoe). Then, we bend an angle of 45°. Now the tube is repositioned and we bring the second marking on the tube to the 45° line marking on the tube bender (shoe). Double-check you are set for the correct bend direction. Then an angle of 45° is bent again.
TUBE BENDING COMING UP TO REQUESTED DIMENSIONS (CONT.)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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Latch
Figure 249
Form Handle
Tube 3/8“
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Bending Form
Shoe
Tube Bending to Requested Dimension 3
Shoe Handle
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Figure 250
Material/Diameter/Thickness Table
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Ref. AMM A340 / ATA 20--23--00
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Lay Lines Lay lines run along the length of a hose. They are yellow, red or white stripes, incorporating MIL-SPEC numbers and various other manufacturers’ information. Besides identifying the hose, it serves to indicate whether the assembly is twisted when installed.
Applications There are essentially three types of hose ratings: S Low pressure ................. up to 600 pounds per square inch (psi) S Medium pressure .......... up to 3000 psi S high pressure ................. 3000 psi +
Why hoses? Flexible hoses are used extensively on aircraft to connect stationary to moving parts and in areas of high vibration.
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Page: 494
Inspection At designated intervals, hoses should be inspected for deterioration. Particular attention should be paid to indications of leakage and mechanical damage (braid separation from the covering or broken wire braids). Damage limits will be found in the SRM.
Construction Hoses are built up from layers. S The inner layer carries the fluid and therefore must be compatible (chemically) with the fluid being transported and have the minimum amount of porosity. The four main compounds used to construct inner liners are Neoprene (for petroleum-based fluids) Buna-N (better suited for petroleum-based fluids) Butyl (phosphate ester-base hydraulic fluid (Skydrol)) Teflon (compatible with almost every fluid carried). S Reinforcement layers cover the inner liner and determine the hose’s strength. Common materials used for reinforcement layers are cotton rayon polyester fabric carbon-steel wire stainless steel wire braid. Diligent design of reinforcement layers can minimise the dimensional changes of hoses under pressure. S The protective outer cover is usually made of rubber-impregnated fabric or stainless steel braid. It is put over the reinforcement to protect from physical damage or heat.
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General Hoses (including fittings) are produced mainly by a manufacturer. It is unusual to fabricate hose assemblies. Fitted hoses must meet the following requirements: S there must be a certain amount of slack between both fittings because hoses reduce their length by between 2% and 4% and expand in diameter when under pressure. Tensile stress on the fittings is unsafe and therefore not permitted. S they must not twist when the end-fittings are tightened. Twisted hoses have a shortened life and can be damaged or buckle when there is movement. End-fittings can loosen off.
HOSES
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High pressure
Medium pressure
Low pressure
A lay-line is a visual indicator for twisting
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 251
Flexible Hoses
Assembly length
Hose length
Swaged fittings require special machinery to assemble and cannot be reused.
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PRESSURE TESTING IS NORMALLY THE RESPONSIBILITY OF SPECIALISTS. A HOSE THAT BURSTS UNDER PRESSURE CAN CAUSE SERIOUS OR EVEN FATAL INJURIES.
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CAUTION:
Cleaning and Pressure-Testing The completed hose assembly must be cleaned out internally with compressed air (blown from both directions alternately) and then proof-tested (normally at 1 1/2 times working pressure) by capping one end.
Method Determine the length of hose required (usually using old assembly as pattern). Protect the outer covering by wrapping with tape, then cut the hose to length with a fine-tooth saw, ensuring both ends are square-cut. 1. With the socket held firmly in a vice (using suitable protection for its surface) and the tape removed, screw the hose into it. Having bottomed the hose in the socket, back it off approximately half a turn. 2. With the socket still held firmly in the vice, force the lubricated end of the assembly tool into the hose sufficiently far for the nipple to be inserted. 3. Using the assembly tool, the nipple is then screwed into the socket, squeezing the hose tightly between socket and nipple. 4. Finally, back off the nipple to leave a gap, permitting the nut to turn freely.
Reusable Fittings It is possible to re-manufacture certain hose assemblies by re-using the end-fittings (the socket, nut and nipple). Prior to this, however, it is important to thoroughly inspect the salvaged fittings for wear or other damage. If any doubt exists as to the item’s serviceability, it is to be discarded.
HOSES (CONT’D)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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Breakdown of Reusable Hose Fitting
Nipple
Nut
Socket
Hose
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Hose
Shoulder of Socket
Hose
Figure 252
Vice Jaws
Assembly Tool
Reusable Hose Fittings
Shoulder of Socket
Socket
2. Lubricate assembly tool and force into hose to open inner liner.
Vice Jaws
1. With socket held in vice, screw hose into socket.
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Nut
Adaptor
Swivel Type
1/32 to 1/16 inch clearance
Page: 497
4. After installation there should be clearance between nut and socket to permit nut to turn freely.
Assembly Tool
Nipple
Use wrench on hex
3. Nipple is screwed into socket with assembly tool.
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Hose Installation There are a number of checks to carry out prior to installing a flexible hose. Inspect the hose for: S applicability S length S cleanliness S damage. Check the hose identification tag for: S part number S cure date (within limits) S assembly date (within limits) When fitting a hose assembly, it is important: S not to twist it, thereby placing it under undue strain. Check the lay line printed along the hose length S that it is subjected to the minimum of flexing during operation S that it is supported at least every 24 inches S that it is not stretched tightly between its fittings 5--8% slack must be present to allow for contraction in length of pipe when pressurised. S that the minimum bend radius is observed.
HOSES (CONT’D)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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✔
✘
Flexure
M7 MAINTENANCE PRACTICES PIPES AND HOSES
Figure 253
Prevent twisting
✘
Installation Example 1
Flexure
✘
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✔
✔
Clamp
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TAKE CARE WHEN REMOVING FIRE SLEEVES; EARLY PRODUCTS CONTAINED ASBESTOS.
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CAUTION:
Protective Sleeves There are areas on an aircraft that produce wear (from abrasion) or extreme heat. Flexible hoses must be protected from these dangers with suitable sleeving. Sleeving is available in a variety of materials, including S heat shrink S nylon spiral wrap S Teflon.
Hose Installation (Cont’d) It is possible to replace a short bend radius with an elbow fitting, but the largest possible bend radius is still preferred. The minimum permissable bend radius is determined by the operating pressure, the type of hose and the nominal size. The bend radius required increases when the hose has to carry out movements in the operating condition. If they can move and become twisted, they are to be fixed with clamps to prevent this. Clamps are also necessary where there is a danger to the hoses due to vibration, long lengths or sharp edges. when bonding clamps are fitted to pipelines, paint and anodizing must be removed so that a low resistance electrical path is provided.
HOSES (CONT’D)
M7 MAINTENANCE PRACTICES PIPES AND HOSES
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M7 MAINTENANCE PRACTICES PIPES AND HOSES
✘
✔
Figure 254
Chafe marks
✘
✔
Installation Example 2
Bend radius too small
Clamp too big
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Chafe marks
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M7.10 SPRINGS
M7 MAINTENANCE PRACTICES SPRINGS
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Maintenance In most cases springs are checked for serviceability and any unserviceability is usually rectified by replacement. Checks include: S An inspection for corrosion, damage, we, broken coils and distortion. S Checking for correct free length of coil springs. Compression springs can be checked using a vernier calliper and tension springs are normally in their fully closed state unloaded. S Check for ”springiness”. This may require a special process using masses and checking the extension/change in length with each added mass. A graph is plotted of mass against change in length from which the elasticity of the spring is ascertained. The spring should return to its free length condition when unloaded. Remember, a spring should obey Hookes law (Robert Hooke English physicist 1635 -- 1703) in that extension (or compression) is proportional to the force applied. S If a spring is corroded, it should be discarded even if it appears to function correctly, this is because the spring will have become weak and may fail under load.
IR PART 66 M7.10 (Cat A)
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1. Ensure that the tension springs (1) are correctly attached to the sidestay and the lockstay. 2. Examine the tension springs (1) for: A. impact damage B. distortion C. scores D. corrosion. 3. Examine the end fittings of the tension springs (1) for: A. damage B. cracks C. corrosion. 4. Move the tension springs (1) around their longitudinal axis. This will ensure that the tension springs (1) are free to move in their end bearings. 5. Ensure that the spring eye--ends at the side--stay end are correctly attached to the inner retainer spring. 6. Ensure that the cotter pins (2) and (3) are serviceable and correctly installed. 7. Look at the points D. Ensure that the tension springs (1) do not touch the edges of the side stay.
Airbus A340 Main Landing Gear Lock Springs - Inspection
EXAMPLE
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Definition Springs are any of several elastic devices used variously to store and to furnish energy, to absorb shock, to sustain the pressure between contacting surfaces, and to resist tensional or compressional stress. Springs are made of an elastic material, eg specially formulated steel alloys or certain types of rubber or plastic. A torsion spring that stores energy, eg for operating a watch, is a metal strip wound spirally around a fixed centre. For reducing concussion in some heavy trucks and railroad cars, helical (or coil) springs are used. Coil springs are commonly used for the same purpose in motor cars, as are leaf springs that consist of flat bars clamped together. These have been replaced in some vehicles by torsion bars that absorb stresses by twisting. The helical--coil compression spring provides the force to keep the operating surfaces together in the friction clutch. The extension spring is employed for a spring balance; the distance through which it is extended depends on the weight suspended from it. The disk spring, which consists of a laminated series of convex discs, is widely employed for heavy loads.
M7 MAINTENANCE PRACTICES SPRINGS
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M7 MAINTENANCE PRACTICES SPRINGS
Figure 255
Lock Stay Lower Connector Link
Airbus A340 Main Landing Gear Lock Springs
Side Stay
Side Stay
Lock Stay
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M 7.11 BEARINGS
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There are five basic types of anti--friction bearings: S tapered, needle, ball, spherical and cylindrical. Each is named for the type of rolling element it employs.
ANTI-FRICTION BEARINGS
The journal of a sliding bearing operates in a bearing box, a bearing bushing or directly in the bearing body. Bearings for large journal diameters and bearings that cannot be pushed over the shafts during assembly (eg crankshafts) must be two-part bearings. To decrease friction between journal and bearing, a continuous lubrication film has to exist. For this, bearing play is necessary. The amount of bearing play depends on the demands the bearing is subjected to and the lubricant. Sliding bearings are resistant to push forces, they operate with little noise and they are suitable for both slow and fast rotational journal speeds. Their high starting resistance, however, is disadvantageous. They also require continuous maintenance.
SLIDING BEARINGS
Page: 508
Correct lubrication is vital in all kinds of bearings. It provides a film that separates the bearing’s moving parts, carries away heat and protects bearing surfaces from corrosion. As a bearing rotates, the mating surfaces of its components create a lubricant film in the bearing that separates components, preventing metal-to-metal contact. This action reduces friction and prevents wear and corrosion. Bearings are protected with a preservative coating during storage and shipment.This is NOT a lubricant. However, it IS compatible with the relevant lubricant and need not be washed off prior to installation, but it is essential to lubricate the bearing at installation. Grease is one of the most popular lubricants. It should be packed into the bearing so that it will coat between the rollers and cage. In the case of a tapered bearing, forcing grease through the bearing from the large to the small end will ensure correct distribution. Any excess grease should be smeared on the outside of the rollers. It is important not to over-grease bearings. Too much grease in the housing will cause excess churning and generate extremely high temperatures; potentially a fire hazard.
Bearings are used to support the journals of shafts and axles. Bearings for supporting journals, which are designed to accept forces at rightangles to the drilling axis, are called journal bearings or roller bearings. Bearings for pivot journals, which are designed to accept forces in a longitudinal direction, are called pivot bearings or axial bearings. These are different to sliding bearings or anti-friction bearings.
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LUBRICATION
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BEARINGS (GENERAL)
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Ball
Common Anti-Friction Bearing Types
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Figure 256
Tapered Rollers
Needle Rollers
M7 MAINTENANCE PRACTICES BEARINGS
Spherical Rollers
Cylindrical Rollers
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False Brinelling False brinelling (elliptical wear marks in an axial direction at each ball position with a bright finish and sharp demarcation, often surrounded by a ring of brown debris) indicates excessive external vibration. A small relative motion between balls and raceways occurs in non-rotating ball bearings that are subject to external vibration. When the bearing isn’t turning, an oil film cannot be formed to prevent raceway wear. Wear debris oxidizes and accelerates the wear process. Correct by isolating bearings from external vibration and using greases containing antiwear additives (such as molybdenum disulphide) when bearings only oscillate or reverse rapidly, as in actuator motors.
Overheating Symptoms are discolouration of the rings, balls and cages from gold to blue. Temperatures in excess of 400oF can anneal the ring and ball materials. The resulting loss in hardness reduces the bearing capacity causing early failure. In extreme cases, balls and rings will deform. The temperature rise can also degrade or destroy lubricant. Common culprits are heavy electrical heat loads, inadequate heat paths and insufficient cooling or lubrication when loads and speeds are excessive. Thermal or overload controls, adequate heat paths and supplemental cooling are effective cures.
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Reverse Loading Angular contact bearings are designed to accept an axial load in one direction only. When loaded in the opposite direction, the elliptical contact area on the outer ring is truncated by the lower shoulder on that side of the outer ring. The result is excessive stress and an increase in temperature, followed by increased vibration and early failure. Failure mode is very similar to that of heavy interference (tight) fits. The balls will show a grooved wear band caused by the ball riding over the outer edge of the raceway. Corrective action is to simply install the bearing correctly. Angular contact bearings must be installed with the resultant thrust on the wide face (which is marked “thrust“) of the outer ring and the opposite face of the inner ring.
Normal Fatigue Failure Fatigue failure (usually referred to as spalling) is the fracture of the running surfaces and subsequent removal of small, discrete particles of material. Spalling can occur on the inner ring, outer ring or balls. This type of failure is progressive and, once initiated, will spread as a result of further operation. It will always be accompanied by a marked increase in vibration, indicating an abnormality. The remedy is to replace the bearing or consider redesigning to use a bearing having a greater calculated fatigue life.
True Brinelling Brinelling occurs when loads exceed the elastic limit of the ring material. Brinell marks show as indentations in the raceways which increase bearing vibration (noise). Severe brinell marks can cause premature fatigue failure. Any static overload or severe impact can cause brinelling. Examples include: S Using hammers to remove or install bearings S dropping or striking assembled equipment, and S pressing a bearing onto a shaft by applying force only to the ring being press-fitted, ie do not push the outer ring to force the inner ring onto a shaft.
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Excessive Loads Excessive loads usually cause premature fatigue. Tight fits, brinelling and improper preloading can also bring about early fatigue failure. This type of failure looks the same as normal fatigue, although heavy ball wear paths, evidence of overheating and a more widespread spalling (fatigue area) are usually evident with a shortened life. The solution is to reduce the load or redesign using a bearing with greater capacity.
BEARING DEFECTS AND THEIR CAUSES
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TRUE BRINELLING
Brinell marks ball spaced
Ball path
EXCESSIVE LOADS
M7 MAINTENANCE PRACTICES BEARINGS
Figure 257
Bearing Defects 1
NORMAL FATIGUE FAILURE
Spalled area
Ball path
OVERHEATING
Silver/gold
Blue/black
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Thrust
REVERSE LOADING
Ball band caused by ball riding over edge of raceway
FALSE BRINELLING
False brinell marks
Ball path
Thrust
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Corrosion Red/brown areas on balls, cages or bands of ball bearings are symptoms of corrosion. This condition results from exposing bearings to corrosive fluids or a corrosive atmosphere. The usual result is increased vibration followed by wear, with subsequent increase in radial clearance or loss of preload. In extreme cases, corrosion can initiate early fatigue failures. Correct by diverting corrosive fluids away from bearing areas and use integrally sealed bearings whenever possible. If the environment is particularly hostile, the use of external seals in addition to integral seals should be considered.
Lubricant Failure Discoloured (blue/brown) ball tracks and balls are symptoms of lubricant failure. Excessive wear of balls, ring and cages will follow, resulting in overheating and subsequent catastrophic failure. Ball bearings depend on the continuous presence of a very thin - millionths of an inch - film of lubricant between balls and races, and between the cage, bearing rings and balls. Failures are typically caused by restricted lubricant flow or excessive temperatures that degrade the lubricant’s properties. Any steps taken to correct improper fit, control preload better and cool the shafts and housings will reduce bearing temperatures and improve lubricant life. During inspection both contamination and insufficient lubricant should be carefully checked, otherwise bearing failure may occur
Contamination Contamination is one of the leading causes of bearing failure. Contamination symptoms are denting of the bearing raceways and balls, resulting in high vibration and wear. Contaminants include airborne dust, dirt or any abrasive substance that finds its way into the bearing. Principle sources are dirty tools, contaminated work areas, dirty hands and foreign matter in lubricants or cleaning solutions. Clean work areas, tools, fixtures and hands help reduce contamination failures. Keep grinding operations away from bearing assembly areas and keep bearings in their original packaging until you are ready to install them. Seals are critical - damaged or inoperative seals cannot protect bearings from contamination.
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Tight Fits A heavy ball wear path in the bottom of the raceway around the entire circumference of the inner ring and outer ring indicates a tight fit. Where interference fits exceed the radial clearance at operating temperature, the balls will become excessively loaded. This will result in a rapid temperature rise accompanied by high torque. Continued operation can lead to rapid wear and fatigue. Corrective action includes a decrease in total interference - better matching of bearings to shafts and housings - taking into consideration the differences in
Loose Fits Loose fits can cause relative motion between mating parts. If the relative motion between mating parts is slight but continuous, fretting occurs. Fretting is the generation of fine metal particles which oxidize, leaving a distinctive brown colour. This material is abrasive and will aggravate the looseness. If the looseness is enough to allow considerable movement of the inner or outer ring, the mounting surfaces (bores, outer diameters, faces) will wear and heat, causing noise and runout problems.
Misalignment Misalignment can be detected on the raceway of the non-rotating ring by a ball wear path that is not parallel to the raceway edges. If misalignment exceeds 0.001in/in you can expect an abnormal temperature rise in the bearing and/or housing and heavy wear in the cage ball-pockets. The most prevalent causes of misalignment are: S bent shafts S burrs or dirt on shaft or housing shoulders S shaft threads that are not square with shaft seats, and S locking nuts with faces that are not square to the thread axis. The maximum allowable misalignment varies greatly with different applications, decreasing, for example, with speed. Appropriate corrective action includes: S inspecting shafts and housings for runout of shoulders and bearing seats S use of single point-turned or ground threads on non-hardened shafts and ground threads only on hardened shafts, and S using precision grade locknuts.
The use of stainless steel bearings is also helpful.
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BEARING DEFECTS AND THEIR CAUSES (CONT’D)
M7 MAINTENANCE PRACTICES BEARINGS
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materials and operating temperatures. Increased radial clearance will also increase bearing life under the above conditions.
M7 MAINTENANCE PRACTICES BEARINGS
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MISALIGNMENT
Non-parallel ball path on outer raceway
Wide ball path on inner raceway
CONTAMINATION
Balls wll be similarly dented, dull or scratched
Irregular dents or material embedded in raceways
M7 MAINTENANCE PRACTICES BEARINGS
Figure 258
Bearing Defects 2
LOOSE FITS
Outer ring slippage caused by improper housing fits
LUBRICANT FAILURE
Blue / black raceways
Balls wll be also be blue / black
Silver / gold
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TIGHT FITS
Discoloured, wide ball path at bottom of raceways
Page: 514
Red / brown stains or deposits on rings
CORROSION
Ball path
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When installing bearings, the following basic rules have to be observed: S Check drilling surface and bearings for satisfactory condition S Apply surface protection S Install bearing with a drawing die and make sure that the projecting length is central S Roll the bearing with tools S Check flange S Test the bearing with testing load - if necessary seal gap.
INSTALLATION OF BEARINGS
when removing bearings, the following basic rules must be observed: S Use the correct removal tools S Avoid damage to the structure when using the circular cutting guide S The circular cutting guide must have an exterior diameter which is sufficiently large so that only the flange will be cut S The lower and upper tool must be equipped with adequate bushing guides or guide pins S If possible, use a column-type drilling machine as the drive. After the flange has been cut free, the bearing has to be squeezed out with an ejection tool.
REMOVAL OF BEARINGS
Installation and removal of Boeing aircraft bearings is described in the Boeing Process Specification BAC 5435.
GENERAL INSTRUCTIONS
M7 MAINTENANCE PRACTICES BEARINGS
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Figure 259
Pressure Plate
Bushing
Single-Drum Tool
Bearing Installation Tooling
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Check bearings manually for smooth operation. Bearings that are considered as satisfactory may be installed. Bearings that do not operate smoothly or show signs of jamming must be disassembled and subjected to visual inspection and greasing according to the following instructions: S The following treatment of bearings has to be performed in a well-ventilated, dust-free room with a constant temperature (20o C). Optimum cleanliness during the entire treatment is essential. -- Remove clamping rings and cover plates carefully. Rinse the bearings manually in a container filled with Inhibisol until all grease and other residue has been removed. -- Rinse the cleaned bearings in a second container filled with the same cleaning solution, and then rinse for a third time in another container with the same cleaning solution. -- Cleaning fluids which are used for cleaning and rinsing have to be renewed depending on the number of bearings to be treated, but a minimum of one change per day must be carried out. -- In the case of filtering used cleaning fluids for reuse, filter systems that will remove 98% of all foreign material larger than 10 microns must be used. -- Dry the completely clean bearings with a gentle stream of air. The bearing should not be allowed to rotate.
BEARINGS THAT CAN BE DISASSEMBLED
Check bearings manually for smooth operation; bearings that are considered satisfactory may be installed. Bearings that don’t operate smoothly or show signs of jamming are not suitable for installation.
BEARINGS THAT CANNOT BE DISASSEMBLED
NOTE:
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TREAT THE OUTER BEARING WITH A THIN FILM OF THE SAME GREASE THAT WAS USED FOR FILLING. RE-INSTALL COVER PLATES AND CLAMPING RINGS.
BEARINGS HAVE TO BE GREASED WITHIN TWO HOURS OF THE FINAL RINSE.
AFTER DRYING, THE BEARING HAS TO BE HALF-FILLED WITH GREASE MIL G-3278+Z. USE A NIROSTA SPATULA.
DO NOT TOUCH THE BEARINGS WITH BARE HANDS DURING CLEANING, DRYING AND GREASING. USE RUBBER GLOVES OR TONGS.
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When installing anti-friction bearings in components and aircraft controls (elevator, aileron and rudder), the following instructions must be observed unless otherwise defined in special instructions (refer to process specification).
INSTALLATION OF ANTI-FRICTION BEARINGS
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Figure 260
Typical bearing lubrication device
Bearing Lubrication
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Bearings are protected with a preservative coating during storage and shipment. This is NOT a lubricant. It is essential to lubricate the bearing at installation.
M7 MAINTENANCE PRACTICES BEARINGS
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M7.12 TRANSMISSIONS
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Specifications Chains used for aircraft purposes are generally of the simple roller type to British Standard 228. Chain assemblies are produced to standards prepared by the Society of British Aircraft Constructors (SBAC). These standards provide a range of chains built up in various combinations with standard fittings, eg end connectors with internal or external threads, bi-planer blocks for changing the articulation of a chain through 90o and cable spools for connecting chains to cables having eyesplices.
Introduction Chains provide strong, flexible and positive connections and are generally used wherever it becomes necessary to change the direction of control runs in systems where considerable force is exerted. The change of direction is achieved by the use of sprockets and bi-planar blocks. Chains may be found in S control column installations S aileron and elevator controls S trim control systems. Chains may be used solely in control runs or in conjunction with cable assemblies. Incorrect assembly of chains should be rendered impossible by the use of nonreversible chains in conjunction with the appropriate types of wheels, guards and connectors.
CONTROL CHAINS AND SPROCKETS
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Figure 261
Standard Chain Fittings
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2
4
6
0.375 in
0.50 in
0.50 in
3500 lb
1800 lb
1900 lb
800 lb
Minimum Breaking Load
1166 lb
600 lb
634 lb
267 lb
Proof Load
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1. NO ATTEMPT SHOULD BE MADE TO BREAK AND REASSEMBLE RIVETED LINKS OR ATTACHMENTS. IF IT IS NECESSARY TO DISCONNECT A CHAIN, THIS SHOULD BE UNDERTAKEN ONLY AT THE BOLTED OR SCREWED ATTACHMENTS. 2. THE USE OF CRANKED LINKS FOR THE ATTACHMENT OF THE CHAIN TO END FITTINGS, ETC, IS NOT PERMITTED. THUS WHERE A CHAIN IS REQUIRED TO TERMINATE IN A SIMILAR MANNER AT EACH END, THE LENGTH SHOULD BE AN ODD NUMBER OF PITCHES. FOR THE SAME REASON, AN ENDLESS CHAIN SHOULD HAVE AN EVEN NUMBER OF PITCHES. 3. THE USE OF SPRING CLIP CONNECTING LINKS IS PROHIBITED AND THE ATTACHMENT OF CHAINS TO OTHER PARTS OF THE SYSTEM SHOULD BE EFFECTED BY POSITIVE METHODS SUCH AS PRE-RIVETED OR BOLTED JOINTS.
1
8mm
WARNING:
BS Number
Chain Pitch
Chain Assemblies A simple roller chain consists of outer and inner plates, rollers, bearing pins and bushes. The chain has three principle dimensions (known as gearing dimensions): S pitch S width between inner plates S roller diameter. The pitch of the chain is the distance between the centres of the rollers. For aircraft purposes, four sizes of chain are standardised by the SBAC. The proof-load for a chain should be 1/3rd of the minimum breaking load.
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Figure 262
Chain Details
Typical Chain End Assembly
Bush Outer Plate
Roller
Inner Plate
Outer Plate Bearing Pin
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Roller Diameter
Width between inner plates
Pitch
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Installation of Sprockets During installation, Sprockets should be checked to ensure that they are attached in the manner and method specified by the relevant drawings this should include alignment and positive engagement on the drive shaft. The drive shaft bearings should also be checked for play. The correct positioning of sprockets is of particular importance when non-reversible chains are used. During maintenance, sprockets should be checked for security and wear on the teeth. Pulleys should be checked for damage and excessive wear on the walls and on the chain guide section.
The figure opposite illustrates typical arrangements of chain assemblies. (a) shows the simple transfer of straight-line to rotary motion. (b) illustrates how a change of direction of straight-line motion is obtained. (c) shows a change of direction of motion in two planes by the use of a biplaner block. A range of non-interchangeable end fittings is available as a safeguard against the crossing of controls. However, these connectors do not always prevent the possibility of reversing the chain end to end on its wheel. Neither do they prevent the possibility of the chain being assembled to gear on the wrong face where two wheels are operated by the same chain. Such contingencies can be overcome by the use of non-reversible chains.
Installation of Chain Assemblies New chain assemblies will come prelubricated, this lubrication should not be removed. If a chain assembly is being refitted then it should be lubricated with an approved lubricant as detailed in the AMM. After installation it is important to check the chain for twist and alignment with the sprocket. The chain should run smoothly over the teeth of the sprocket and there should be no tendency for the chain to ride up over the sprocket. Chains need to be pretensioned enough to prevent backlash but not over tensioned. Chain guards should be fitted in such a way that they don’t rub against the chain or allow the chain to jump off it’s sprockets if it loosens off.
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(b)
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Figure 263
(c)
Bi-Planer Block
End-Connector
Typical Chain Assembly Arrangements
End-Connector
End-Connectors
End-Connector
End-Connector
(a)
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A SPECIAL FEATURE, SUCH AS AN ATTACHMENT COLLAR, KEY OR FLAT ON THE SHAFT IN CONJUNCTION WITH A SPECIALLYSHAPED HOLE IS INCORPORATED IN THE WHEEL MOUNTING TO ENSURE THAT IT CAN BE ASSEMBLED ON ITS SHAFT IN ONE DEFINITE POSITION ONLY. (See lower illustration opposite) this is an instance where the use of jockeys is necessary or where contra-rotation of the wheels is required. It can be seen that the feature of non-reversibility does not affect the ability of the chain to gear on both sides.
NOTE:
Non-Reversible Chains Non-reversible chains are similar to standard chains except that every second outer plate is extended in one direction in order to break up the symmetry of the chain. The complete system of non-reversibility involves the use of five features: S the non-reversible chain S the shroud on the wheel S correct positioning of the wheel on its shaft S the chain guard S non-reversible connectors. By providing a shroud on one side of the wheel and making use of the chain guard (see illustration opposite), the reversing of the chain end-to-end on its wheel is not possible.
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Guard
Connectors non-interchangeable
Incorrect
Correct
Mounting on Wheel Y
Connectors non-interchangeable
Non-Reversible Chain Assemblies
Non-Reversible Chain with Jockey Pulley
Guard
Y
Stop Piece
Correct Assembly
Guard
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Figure 264
Incorrect Assembly
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Inspection of Chain Assemblies General. Chain assemblies should be removed from the aircraft for complete inspection at the periods specified in the appropriate Maintenance Schedule. Removal. When it is necessary to disconnect the chains, the assemblies must be removed at design breakdown points. Checking Articulation. The chain should be checked for tight joints by articulating each link through approximately 180o. Checking for Deterioration. The chain should be examined for damage, cracks and wear to plates and rollers and for evidence of corrosion and pitting. Proof-Loading. It is not necessary to proof-load a chain after removal for routine examination. However, if it is desired to replace a portion only of the assembly, proof-loading of the complete assembly is necessary. The proof-load table should be evenly applied and, unless this can be assured, it is considered preferable to fit a complete new assembly.
M7.12 (Cat A)
IR PART 66
1 2 4 6
8mm 0.375 in 0.50 in 0.50 in
28 lb
28 lb
16 lb
12 lb
Tensile Load
Page: 529
3. The percentage extension over the nominal length should be calculated by the following formula:Percentage extension = M - (X x P) x100 XxP M = Measured length under load in inches X = Number of pitches measured P = Pitch of chain in inches. 4. If the extension is in excess of 2% on any section of the chain the whole run should be replaced. 5. If kinks or twists exist the chain should be rejected. Protection and Storage. After the chain has been cleaned, inspected and found to be acceptable, it should be thoroughly soaked in an appropriate oil, time being allowed fro the lubricant to penetrate to the bearing surfaces. If not required for immediate use, the chain should be laid on a flat surface, carefully coiled and wrapped in greaseproof paper, care being taken to ensure the exclusion of dirt and the prevention of distortion, during storage.
BS Number
Chain Pitch
Checking Elongation. If elongation through wear is suspected, the following procedure is to be followed: 1. The chains should be cleaned by immersion in clean paraffin and brushed with a stiff brush. After cleaning, they should be immediately dried by hot air to ensure that no paraffin remains, otherwise corrosion will occur. The chains should be measured when clean but before any oil is applied. 2. The chains should be placed on a flat surface and stretched by the application of a tensile load (see table). The length should then be measured between the centres of the bearing pins, elongation being calculated by the formula given in the next paragraph.
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Maintenance Inspection Chain assemblies should be inspected for serviceability at the periods specified in the relevant Maintenance Schedule. Recommended methods for checking chains is as follows: S The continued smoothness of operation between the chain and the chain wheel or pulley should be checked. If the chain does not pass freely round the wheel or pulley, it should be removed and checked (see ’Inspection of Chain Assemblies’). S The chain should be checked for wear. If it is worn so that the links are loose and can be lifted away from the wheel teeth, it should be removed and checked for excessive elongation (see ’Inspection of Chain Assemblies’). S The chain should be checked for damage, cleanliness, adequacy of lubrication and freedom from corrosion. If the inspection reveals the chain to be corroded or otherwise defective, it should be replaced. S In instances where it becomes necessary to adjust the tension of the chain in systems incorporating turnbuckles or screwed end connectors, care should be taken to ensure that the chain itself is not twisted during adjustment. The connectors should be held firmly while the locknuts are being slackened or tightened.
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M7.12 (Cat A)
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Background The Airbus A340 has a Trimmable Horizontal Stabilizer (THS), which has two elevators for pitch trim control.The elevators are attached to the trailing edge of the THS.The THS is attached to the rear fuselage and moves about an axis to permit pitch trim. The hydromechanical operation system of the THS (referred to as THS actuator) is controlled electrically (by the Flight Control Primary Computers (FCPC)) and mechanically. The THS has a mechanical control system which has the function of a standby system.The pilots can use two control wheels,which are installed in the cockpit centre pedestal, to operate the THS mechanically. Cables transmit the mechanical commands from the control wheels to the mechanical input shaft of the THS actuator. An override mechanism ensures that the mechanical pitch trim commands cancel the electronic pitch trim commands.
A340 Detailed Visual Inspection of the Trimmable Horizontal Stabilizer (THS) Mechanical Control Loop.
EXAMPLE
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IR PART 66
Page: 531
ENSURE THAT THE FLIGHT CONTROL SURFACES ARE CLEAR; MOVEMENT OF FLIGHT CONTROLS CAN CAUSE DAMAGE AND/OR PERSONAL INJURY. 2. In the cockpit, slowly turn the pitch trim control wheels from one stop to the opposite stop. 3. In the avionics compartment, ensure that the toothed belts (View B) have no cracks, delamination of teeth and no wear marks over the full length. 4. Ensure that the chain and the cable can move freely.
WARNING:
Inspection The following is a precis from the Aircraft Maintenance Manual detailing the inspection of the system belts, chains and cables. 1. Ensure that the following components of the mechanical pitch--trim control loop are in the correct condition: A. pitch--trim control mechanism B. chains and gears of the pitch--trim control mechanism and of the THS actuator C. pulleys D. cable tension regulator E. control cables F. THS input shaft.
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INSPECTION OF BELTS, CHAINS AND CABLES
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Drive belt
Control mechanism
Figure 265
Fwd THS control chain
Location of THS Drive Belts
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B737 Stabilizer Ball Nut and Jackscrew Inspection. Examine the parts for wear, using a micrometer or a vernier caliper. Compare the dimensions with the permitted dimensions shown in Fig. 601. Replace the parts that are out of tolerance.
EXAMPLE
INSPECTION OF SCREWJACKS
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Page: 533
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1. Yoke/bushing (2 locations)
3. Bushing/pin (2 locations)
2. Fitting/pin (2 locations)
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Screwjack gearbox
Ball nut
Screwjack
B737 Stabilizer Ball Nut and Jackscrew Inspection
See view (right)
Figure 266
M7 MAINTENANCE PRACTICES TRANSMISSIONS
Upper gimbal
Page: 534
Lower gimbal
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Minimum backlash: occurs when all tolerances give the shortest centre distance and the thickest teeth at the highest point of pitch line runout. Maximum backlash: occurs when all tolerances give the greatest centre distance and the thinnest teeth at the lowest point of pitch line runout. Backlash Tolerance: the allowable amount of backlash. Backlash Variation: the difference between the maximum and minimum backlash occurring in a whole revolution of the larger of a mating pair of gears.
Definitions
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Page: 535
Backlash in a gear train Backlash can be measured in a gear train by locking one end of the train, and then measuring the limits of movement at the other end of the gear train. The measurement can be made using a DTI that is placed against the so that it measures tangential movement. In the example below, if the backlash in each gear is 0.001mm then the total backlash would be .003mm
Purpose of Backlash The general purpose of backlash is to prevent gears from jamming and making contact on both sides of their teeth simultaneously. A small amount of backlash is also desirable to provide for lubricant space and differential expansion between the gear components and the housing. On the other hand, excessive backlash is objectionable, particularly if the drive is frequently reversing or if there is an overrunning load.
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Maintenance of gears When inspectng gear mechanisms the following lists of defects may be found: S Corrosion is unlikely to affect gears as they are continually woking in a well lubricated environment. If corrosion is found the gear is unserviceable. S Cracks will lead to the gear being replaced. S Erosion is caused by cavitation and will effect gears over extended periods of time. Erosion requires gear replacement. S Chipped/missing teeth will require replacement S Wear limits are laid down in the relevant AMM. S Uneven wear as shown below S Backlash is -- the amount by which the width of a tooth space exceeds the thickness of the engaging tooth on the pitch circles -- the play between mating tooth surfaces at the tightest point of mesh in a direction normal to the tooth surface when the gears are mounted in their specified positions. -- The amount of backlash in a pair of mating gears can be affected by: -- changes in centre distance -- variance in tooth thickness -- temperature ranges causing differential expansion of the gears and mountings.
GEARS
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Helical Gear
Hypoid Gear
Bevel Gear
M7 MAINTENANCE PRACTICES TRANSMISSIONS
Figure 267
Helical gears are similar to the spur gear except that the teeth are at an angle to the shaft, rather than parallel to it as in a spur gear. Helical gears may be used to mesh two shafts that are not parallel, although they are still primarily used in parallel shaft applications.
the teeth are hyperboloid in shape. Additionally the shafts do not intersect
Hypoid gears are like bevel gears, except
Bevel gears are primarily used to transfer power between intersecting shafts and can be used for any angle up to 1800
Types of Gear
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Worm Gear
Spur Gear
Worm gears are special gears that resemble screws, and can be used to drive spur gears or helical gears.
Page: 536
Spur gears are the most commonly used gear type. They are characterized by teeth which are perpendicular to the face of the gear.
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Figure 268
Uneven gear wear
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M7.12 (Cat A)
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M 7.13 CONTROL CABLES
M7 MAINTENANCE PRACTICES CONTROL CABLES
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M7.13 (Cat A)
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Cable lines have advantages over other mechanical actuators, such as linkages, shafts and chains, predominantly weight-saving. Cable lines are used in many applications and can be routed into almost every space via guiding pulleys or deflector rolls. Handling, checking, adjustment and stretching are relatively easy. Cables used in airplane construction normally consist of individual cable wires with a minimum tensile strength of 1200N/mm2 at a breaking elongation of 2 or 7%. The steel wires are twisted into strands and these are twisted into cables. Normally the wires are twisted in one direction and strands the opposite. The number of steel wires in one strand and the number of strands in one cable are the result of the following calculation: S 3/32 - 7x7 or S 1/8 - 7x19 In this calculation the fractional numbers stand for the diameter of the cable (inch). The first figure tells you that the cable consists of 7 strands and the last figure tells you how many steel wires there are in a strand.
CABLE LINES (GENERAL)
M7 MAINTENANCE PRACTICES CONTROL CABLES
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 269
Build-Up of Cables
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Control cables must be handled and stored carefully in order to avoid kinking in the cable. New cable should be supplied on wooden drums that are at least 40 times the diameter of the individual cable itself. Cable should be unwound from a reel that has been mounted on a spindle. After cutting lengths of cable off the drum they should be coiled into radii of not less than 50 times the cable diameter and never in a diameter of less than 150mm (6in). Cable should always be cut with cable cutters or heavy duty pliers but or alternatively, they can be cut using an anvil, hammer and chisel. Cable should never be cut using a flame (e.g. an oxyacetylene cutting torch). After cutting, the cable ends on both the cut length and the drum should be tied with strong cord to prevent their ends from splaying.
CONTROL CABLE HANDLING
M7 MAINTENANCE PRACTICES CONTROL CABLES
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 270
Tying cable ends
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M7.13 (Cat A)
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WEAR GLOVES WHEN YOU TOUCH THE CABLES. BROKEN STRANDS CAN INJURE YOU. 1. Check for broken wires. A. The very important areas where the wires can break are the lengths of the cable that go through fairleads and around pulleys. B. Examine the cables. Ensure that there are no broken wires. To do this: -- move a cloth along the cable, in two directions. -- If the cloth catches on the cable: S make a visual inspection to find the broken wires. -- The permitted limits for the cables with broken wires are: S for class 7 x 19 cable, 6 broken wires in a same one--inch (25.4 mm) length of cable with not more than 3 broken wires for each strand. S for class 7 x 7 cable, 3 broken wires in a same one--inch (25.4 mm) length of cable with not more than 2 broken wires for each strand. Note: there must not be broken wires in two consecutive one--inch (25.4 mm) lengths of cable. For the lengths of cables which can touch pulleys or go through fairleads and pressure seals, not more than 3 broken wires is permitted. 2. Check of the external wear of the cable. A. Make a visual inspection of the cables, especially the lengths that can touch pulleys, fairleads or pressure seals. Ensure that they are not worn. -- The permitted wear limits in a same one--inch (25.4 mm) length of cable are: S for class 7 x 19 cable, a maximum of 6 wires worn to 50% or more of their diameter S for class 7 x 7 cable, a maximum of 3 wires worn to 50% or more of their diameter, if there are no broken wires.
WARNING:
Check of Control Cables and Pulleys
M7.13 (Cat A)
IR PART 66
Page: 544
Note: the number of permissible worn wires in a same one--inch (25.4 mm) length of cable is decreased by one wire for every broken wire. A maximum of two one--inch (25.4 mm) lengths of cable with wear (within the limits specified above) is permissible on the total length of the cable (between the two cable terminals) on the condition that the wear is not on two consecutive one--inch (25.4 mm) lengths of cable. If a wire is worn to more than 60 % of its diameter, you must call it a broken wire. 3. Internal cable wear. A. In some areas (for example around pulleys and quadrants) the cable can wear internally more than it wears externally. To find such wear, move the strands apart to examine the cable internally. 4. Corrosion. Note: Corrosion of cables specially occurs in these areas: S battery compartments S toilets S landing gear wells S other areas where fumes, vapours and liquids that can cause corrosion can collect. A. If a cable has a broken wire in a length that does not touch airframe components which can make it wear (pulleys, fairleads etc): -- carefully examine the cable. Ensure that it has no corrosion. -- If necessary, remove the cable. Bend the cable to make sure that the internal strands do not have corrosion. B. If you find surface corrosion: -- loosen the cable, -- make a full inspection of the inner strands. C. Discard the cable if you find corrosion on the inner strands. D. If you find light surface corrosion, remove it and protect the cable again. Cables should also be inspected for kinks, bird caging, and stretching (beyond limits)
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All cables in an aircraft, especially control cables, require careful inspection at regular intervals in order to ensure their satisfactory function and serviceability at all times. (Extract from Airbus A340 AMM)
INSPECTION OF CABLES
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Individual outer wires worn less than 40% (worn areas individually distinguishable)
Individual outer wires worn 40--50% (note blending of worn areas)
Individual outer wires worn more than 50%
M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 271
Cable Inspection (A320)
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0.011 in.(0.30 mm)
0.015 in.(0.40 mm)
0.019 in.(0.50 mm)
Less than or equal to 1.181 in.(30 mm)
From 30 mm to less than 3.149 in. (80 mm)
More than or equal to 3.149 in.(80 mm) 0.007 in.(0.20 mm)
0.007 in.(0.20 mm)
0.005 in.(0.15 mm)
Max. Eccentricity at Bottom of Groove
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4. Inspection of pulley wobble A. Do a wobble check at each turn of the pulley. S For pulley with a diameter less than 80 mm (3.1496 in.), the wobble must not be more than 0.25 mm (0.0098 in.). S For pulleys with a diameter of 80 mm (3.1496 in.) or more, the wobble must not be more than 0.30 mm (0.0118 in.).
Max. Eccentricity at Top of Groove
Pulley Small Diameter
(Extract from Airbus A340 AMM) 1. Examine pulleys for cracked edges, signs of incorrect wear in the bottom of the groove, cracked hub, excessive play. 2. Examine the pulleys while in operation: S ensure that the pulleys turn freely S ensure that the cable does not skid in the groove. 3. Ensure that the eccentricity agrees with the values shown in this table:
INSPECTION OF PULLEYS
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Figure 272
Pulley Inspection (AMM A320)
Normal pulley wear
Badly-aligned cable
Pulley too big for the cable diameter
Jammed pulley
Badly-aligned pulleys
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Cable tension too high
M7 MAINTENANCE PRACTICES CONTROL CABLES
Pulley flange
Pulley flanges
Page: 547
M7.13 (Cat A)
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IT IS IMPORTANT TO POSITION THESE DISCS CORRECTLY. TRANSPOSING THEM WILL RESULT IN THE TRANSITION AT THE SLEEVE OF THE TERMINAL BEING SHARP-EDGED, WHICH IS NOT PERMITTED UNDER ANY CIRCUMSTANCES. After the rolling discs have been installed on the support shaft of the expanding machine, they are mounted with discs and bolts. The rolling disc with two pins can only be turned counter--clockwise. When the shanks of the machine are moved away from each other, the rolling discs will not turn. When the shanks are pressed together, the rolling discs move in opposite directions via a pair of gear wheels with a ratchet. The shanks are opened and closed until the sleeve of the terminal has rounded the circumference of the rolling disc.
NOTE:
Description of Tools Equipment for rolling on terminals consists of S Several sets of rolling discs S Several sets of “Swaging Rolls“ for balls S A caliper gauge for terminals S A caliper gauge for balls S Allen key for the screws of the rolling disc mountings. Rolling discs for terminals and balls are made for several cable diameters and are marked accordingly. “LOWER“ is the designation for the rolling disc with two pins. “UPPER“ is the designation for the rolling disk with two holes. When the expanding machine is placed on the two shanks, the “LOWER“ disc is down and the “UPPER“ disc is up.
ROLLING ON TERMINALS
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Figure 273
Hand-Operated Rolling Tool
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M7.13 (Cat A)
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THE CABLE DIAMETER IS INDICATED AT THE FRONT OF THE ADAPTER. MOVE A SHORT PART OF THE CABLE INTO THE TERMINAL AND BEND IT. THE END OF THE CABLE WILL BE TIGHT WHEN COMPLETELY PUSHED INTO THE TERMINAL.
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NOTE:
Roll on a sleeve terminal as follows: S Check the sleeve diameter of the terminal using the caliper gauge. The terminal sleeve must fit into the respective test hole of the gauge marked “SLEEVES“. The ball must fit into the test hole marked “BALLS“. The cable diameters are marked on the gauge at the respective holes. S Select and clean the rolling discs suitable for the respective cable diameter. S Install the rolling disc with the two pins and the inscription “LOWER“ in the lower support shaft, and the rolling disc with the inscription “UPPER“ and the two holes in the upper support shaft of the expanding machine. Fix both discs with the washers and screws. S Install the guide. S Make sure that the correct adapter for the cable diameter is installed.
ROLLING OF SLEEVE TERMINALS
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Figure 274
Inserting Cable in Terminal
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S
S
S
S S
May 2004
IT IS NOT PERMITTED TO PERFORM MORE THAN FOUR ROLLING SEQUENCES. EXCESSIVE ROLLING CAUSES BRITTLENESS AND HARDENING OF THE MATERIAL OF THE TERMINAL. Perform the rolling procedure quickly. After the first operational sequence, a rolling mark will appear on the sleeve of the terminal. Turn the terminal about 90o to compensate for this rolling mark and perform a second operational sequence as described. After the second operational sequence, the terminal sleeve must not show deep impressions. Check the diameter of the terminal sleeve with the caliper gauge as described. A slight rolling mark is permitted. The diameter of this rolling mark must not exceed the sleeve diameter by more than 0.010 in. If the diameter of the sleeve terminal has not been tapered sufficiently, a third operation sequence must be carried out. For this you must rotate the terminal through 90o. In case a fourth operation sequence is necessary, the terminal must be turned about 90o again.
CAUTION:
S Mark the cable which has been completely inserted into the terminal at the end of the sleeve of the terminal with chalk or tape in order to indicate if the cable slips out. S Turn the rolling discs into the starting position, using the two pins. S Press the terminal against the conical guide of the adapter and clamp the cable into the clip at the guiding-device. S Push the guiding device with the terminal into the starting position for the rolling procedure. S Turn the rolling discs using the two pins until the terminal is clamped.
ROLLING OF SLEEVE TERMINALS (CONT.)
M7 MAINTENANCE PRACTICES CONTROL CABLES
Page: 552
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 275
Go No-go gauging
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Page: 554
Rolled-on balls and terminals are checked for sufficient tensile strength by using the Cable Terminal Pull Tester. The Pull Tester consists of a vice with steel cheeks with inserted copper cheeks and a gauge. When, for instance, a 1/8“ cable and terminal are checked, you must first select the correct copper cheeks. These must then be inserted into the steel cheeks. The correct swivel for the terminal must be selected. The cable with the swivel is attached to the test device. The copper cheeks are tightened with two clamping screws to the extent that the cable cannot slacken under the test load. By turning a hexagon head screw, the cable is tightened with hydraulic power. The scale of the indicating device shows the load in pounds. The scale has load marks for the respective cable diameter. If not, you must refer to a test table. After one or two minutes the pointer has to be returned to the load mark. The full test load should be applied for 5 seconds. Then take off the tension slowly and evenly.
Check manufactured cable lines according to the following instructions: S Check final dimensions S Check terminals for specified diameters (use caliper gauge of the terminal expanding machine) S Visual check of the terminals S Use magnifying glass (6x magnification). There must be no cracks, notches or abrupt changes in cross-section. S Check satisfactory stability of connection. All connections between cable and terminal must be subjected to a test of their tensile strength. In this check, you must evenly apply the respective test pull force (given in a table), observing the specific speed with which the tension may be increased. You must also observe the duration over which the full test pull force is allowed to be applied. Note: If a slippage between cable and terminal is indicated during this test (by means of marks that have been applied to the cable before the test), the connection is not stable enough. This cable line has to be either discarded or the cable can be used for shorter cable lines after the terminals have been cut off. If the test is performed without slippage, the connection is considered as satisfactory.
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Cable Terminal Pull Tester
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Tools: Cable Terminal Pull Tester AT520CT
INSPECTION OF MANUFACTURED CABLE LINES
M7 MAINTENANCE PRACTICES CONTROL CABLES
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 276
Pull Tester AT520CT
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Page: 556
NEVER LOCK THE BRAKE LEVER ROD UNTIL THE INSTRUMENT IS CLAMPED ON THE CABLE OR A FALSE READING MAY RESULT. The gauge is not marked in specific units. Convert the dial reading to tension in pounds by referring to the calibration chart attached to the lid of the carrying case. For example, the dial reads 59 on the 1/16 inch cable and is converted to 150 pound tension by referring to the calibration chart.
CAUTION:
The cable tensiometer is a precision instrument designed for rigging control cables. The entire operation of testing cable tension can be done with one hand. The size of the instrument permits entry through small openings, so that cables in confined areas can be tested and its tension read. The tensiometer must be handled as a precision instrument, and calibrated annually to ensure that the indications are correct. CAUTION: Before the tensiometer is used, be sure the correct riser is mounted on the instrument for the size cable to be tested. This information is given on the calibration card in the instrument carrying case. The tensiometer should be operated as follows : S Move the trigger away from the case as far as possible and place the instrument on the cable with sectors resting against the cable. Tension should not be taken next to a terminal end or turnbuckle, as an inaccurate reading could result. S Close the trigger with the fingers of the hand in which the instrument is held. Do not twist or pull; this may cause a false reading. Do not let the trigger snap against the case, as this may also give a false reading. The tension should be checked three or four times, moving the instrument slightly along the cable. If the dial is visible, take the reading and then disengage the instrument by moving the trigger away from the case. If the dial cannot be seen, the pointer is locked in position by pushing the small brake lever rod at the top left of the case forward. The pointer is unlocked by returning the brake rod to its original position.
Installed cable lines have to be tightened to a certain tension depending on their location and purpose. A newly-manufactured cable that is delivered by the meter, coiled on a reel, would increase its length under load. This is the reason why it is necessary to preload the cables before they are made into cable lines. The pre-stretch load equals the test load and can be found in the respective table of the manual. The tension applied has to be done with a steady speed. The load must be applied for 5 minutes. The cable is only allowed to be preloaded when it is not bent. In the case of cables longer than 30m, the cable may be preloaded over a movable guide pulley. Correct tension is essential because loose cables cannot transfer control inputs. Loose cables can also lock and thus endanger the airplane and occupants. Cables with excessive tension are also undesirable in airplanes. They can damage pulleys and support structure etc. When the cable tension is adjusted, the ambient temperature is important. In flight, temperatures may vary to a high extent between the ground temperature at the departure airport, the ambient temperatures during flight and the temperature at the destination. Large differences in tensions are created, because the airplane is manufactured from aluminium alloy and the cables are made from steel. The tension values to be adjusted for the individual aircraft types are therefore specified in the respective AMMs. The cable is tightened by turning a turnbuckle. A spring wire clip has to be inserted into the barrel hole of the terminals to prevent the terminals from turning with the cable. The side of the left-hand thread of the turnbuckle is marked by a groove. When tightening cables, they must be tensioned evenly throughout the system otherwise correct system rigging may be difficult to achieve and some turnbuckles may be out of safety. A turnbuckle is in safety when the threaded portion of the turnbarrel assembly is visible through the safety inspection hole. This is often check using locking wire that is inserted into the inspection hole. If it pushes through the inspection hole and out through the reverse hole then the turnbuckle is NOT safe.
M7.13 (Cat A)
IR PART 66
CABLE TENSIOMETER
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CABLE TIGHTENING AND MEASURING TENSION
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 277
Cable Tensioning
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Locking turnbuckles Locking of turnbuckles employs either: S Wirelocking, the gauge and type of locking wire is given in the AMM. S Lock nuts. S Special locking clips.
M7 MAINTENANCE PRACTICES CONTROL CABLES
Page: 558
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 278
Locking turnbuckles
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Cable and Conduit Cable and conduit is relatively lightweight and installation is simple compared with other methods of remote control. Teleflex and Bowden are typical methods of cable and conduit control, in which each system consists primarily of a cable passing through a covering (conduit) fitted with appropriate end fittings. In principle, if the conduit is bent, a pull on the cable will tend to straighten the conduit, but because of the natural stiffness and the fact that the ends of the conduit are fixed, straightening is prevented.
Remote Control Methods Chains, sprockets, pulleys, cable, levers and rods are used for remote control, but advantage may be gained by the use of a cable and conduit since the control can be bent to pass through the structure.
Introduction Manually-operated remote controls are installed in aircraft to operate, from the flight deck, such components as trim tabs, brake control valves and engine controls. They can also be adapted for other uses such as the indication of landing gear movements, position of flaps etc.
CONTROL CABLES
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Single-Entry Unit
180o Double-Entry Unit
Nipple-Type Connector
Typical Remote Control System
Teleflex
90o Double-Entry Unit
Clamp Block
Anti-Torsion Tube
Clamp-Type Connector
Junction Box
Quick-Break Unit
Spent Travel Tube
Swivel Joint
Straight-Lead Unit
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Figure 279
Sliding End Fitting
Rotary Movement Not Exceeding 90o
M7 MAINTENANCE PRACTICES CONTROL CABLES
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BECAUSE OF THE DIFFERENCE IN THE LAY OF THE CABLES (LEFT-HAND AND RIGHT-HAND) THEY ARE NOT INTERCHANGEABLE. EG A No 2 CABLE MUST BE USED WITH A No 2 TRANSMITTING UNIT.
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NOTE:
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SUPPORT MUST BE GIVEN TO BENT PORTIONS OF THE CONDUIT, BUT CLAMP BLOCKS, SPACED 3 FT APART, SHOULD BE USED TO SECURE STRAIGHT PORTIONS TO THE AIRFRAME.
Page: 562
Sliding End Fittings These are used where it is not necessary to convert the pull-push movement of the cable into a rotary movement; they are used in lieu of wheel units. Various types of sliding end fitting are available, each comprising a guide tube terminating in a fork, eye, ball joint or an internal or external threaded fitting. The cable is attached to the end fitting by means of a special collet attachment or by means of a lock spring and plug.
NOTE:
Conduits The rigid conduits normally used in aircraft are of light alloy, although steel and tungum conduits are used for special purposes. It may be bent in smooth curves to radii of not less than 3 inches. Where there is relative movement between conduit and component, flexible conduit may be fitted, but to avoid backlash only the minimum length should be used. Flexible conduit may be bent to a radius of not less than 9 inches.
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Cables The cable consists of a tension wire wound either with a continuous left- or right-hand helix winding which engages with the teeth of gear wheels at the transmitting and receiving ends of the control run. The helix winding may also be used as a thread by which various end fittings can be attached to the cable. The cable is designed for transmitting both pull and push. There are two types of cable in use: 1. No 2 Cable. This cable is built up from a high-tensile steel wire which is wound with a compression winding. The latter is wound with a left-hand helix winding which is pitch-spaced by a spacer winding. The cable is 3/16“ diameter. 2. No 380 Cable. This cable is built up from a high-tensile steel wire which is wound direct with a right-hand helix winding and spacer winding. In this method of construction there is improved efficiency and a reduction in backlash, particularly when the cable is under compression. The cable is 3/16“ diameter.
TELEFLEX CONTROLS
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Tension Wire
Spacer Winding
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No 2 Cable
Compression Winding
Figure 280
M7 MAINTENANCE PRACTICES CONTROL CABLES
Helix Winding
Fork end
Eye end (fork joint)
Ball and socket end
End screwed to take fitting
Ball Ends
Types of Teleflex Cable and Typical Sliding End Fittings
No 380 Cable
Tension Wire
Spacer Winding
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Page: 564
5. Junction Box Unit. These are installed where it is necessary to reverse the direction of travel of the control cables, or to branch a run of cable so as to operate two components (eg on both port and starboard sides of the aircraft). In one type the box contains a gear wheel and provision is made for two cables to pass through the box, one on either side of the gear wheel. The gear wheel may be rotated to move both cables, or one cable may operate the gear wheel which in turn operates the other cable. 6. Swivel Joints. This can be installed where rotary movement of the control lever at the receiving end does not exceed 90o. This type of joint consists of a ball and socket connection inside a housing attached to the end of the rigid conduit. The housing must be rigidly secured to the aircraft structure. The ball is welded to a length of tubing of the same size as the conduit. A suitable sliding end fitting is attached to the end of the control cable so that the guide tube slides freely over the swivel joint tube.
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End Fittings The transmitting end of a control is usually fitted with a wheel unit consisting of a hand-operated gear wheel enclosed in a casing. Alternatively, where the control loading is light and the control run fairly straight, a pull-push operating handle can be used. At the remote end, the cable operates an appropriate wheel unit or is coupled, by means of a sliding end fitting, direct to the actuating mechanism on the component being controlled. Swivel joints are also provided to take up the angular movement of an actauting lever at the end of a control run. 1. Single-Entry Unit. In this wheel unit the cable enters the unit by means of a conduit connector and is led into a slot in the gear wheel. The rotary travel of the unit is limited to 270o of travel of the gear wheel and a minimum of 40o engagement must be maintained at all times between the gear wheel teeth and the cable. 2. Double-Entry Unit. Where greater travel than can be obtained with a single-entry unit is required, a double-entry unit may be used. In this wheel unit the cable enters the unit by means of a conduit connector and, after wrapping round the gear wheel, emerges via another conduit connector at a point 90o, 120o or 180o from the point of entry. The end of the cable that emerges from the unit may be accommodated in a short length of conduit known as a spent travel tube. 3. Anti-Torsion Tube. It is sometimes necessary to prevent the control cable from turning in the conduit and so altering the relative adjustment. This is done by installing an oval-sectioned anti-torsion tube in place of a spent travel tube. This tube serves as a guide to an oval ferrule secured to the spent travel end of the cable. 4. Straight-Lead Unit. In this unit the cable passes straight through and consequently engages on only a few teeth of the gear wheel. Therefore, these units are not suitable for heavily-loaded controls. It can be interposed in a control run or fitted at the transmitting or receiving ends of a control.
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Cable
Conduit Connector
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Straight Lead Unit
Single-Entry Unit
Gear Wheel
M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 281
Spring
Bearing Circlip
Swivel Joint
Body
Ball End (welded to conduit)
Conduit
Return Spring (Optional)
Pull-Push Control Unit
Attachment Coil (Lock Spring)
Cable Lock Nut
Conduit Connector Nipple
Teleflex System Components
Junction Box Unit
Double-Entry Unit
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Conduit
Page: 565
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End Fittings (cont’d) 7. Torsion Drive. In certain installations the final linear movement of the control is converted to rotary action by the use of a distributor box coupled, via a torsion drive, to the component to be operated. The torsion drive is similar to a normal flexible drive. 8. Distributor Box. This is similar in construction to a receiver unit with a gear wheel attached to the face of the cable gear wheel. The attached gear wheel drives a pinion on a cross shaft which engages with one or two tongue ends of the torsion drive cable. To convert the rotary motion of the torsion drive to the linear movement of a trimming tab, a sprocket-driven screw jack may be used. To prevent vibration from affecting the setting of a wheel unit control, or to lock the control in any position, a damping device may be fitted. This device consists of a spring-loaded friction plate pressed against the gear wheel.
M7 MAINTENANCE PRACTICES CONTROL CABLES
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M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 282
Cable
Torsion Drive
Screw Jack
Teleflex Distributor Box and Torsion Drive
Distributor Box
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Quick-Break Units Quick-break units of various types are installed in control runs to facilitate removal of components without disturbing the control. The cable joining fittings are similar in all types of quick-break unit and consists of rods machined with interlocking slotted ends attached to the ends of the cables.
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IR PART 66
Remove sliding tube from end of cable and test for freedom. If stiff, fit new parts. Check alignment of swivel joint (if fitted). Renew damaged parts and reset the assembly. Renew wheel unit.
Lack of lubricant in conduit.
Bent sliding end fitting.
Fouling between end fitting and airframe due to damage or faulty installation. Worn wheel unit gear wheel, allowing cable to override.
Page: 568
Dismantle, clean, assemble and test. If unsatisfactory, renew swivel joint.
Dismantle end fittings and remove the cable from the conduit. Smear the cable with high-altitude grease and re-assemble.
Kinked cable.
Jammed swivel joint.
Renew cable.
Damaged conduit.
Remedy (a) Flexible type - renew complete conduit. (b) Rigid type - cut out damaged portion and renew.
Probable Cause
Servicing Servicing of the control system consists of checking its operation, examining for wear and damage, renewing defective parts and periodical lubrication. Stiff control movement may be caused by the following:
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Conduit Connectors Some conduit connectors are similar in construction to all-metal pipe couplings without an olive. The standard nipple-type connector consists of a screwed nipple that is threaded onto a rigid conduit, before the conduit is flared. The nipple is then screwed into a wheel unit or conduit connector body, thus retaining the conduit secure against a shoulder in the internally-threaded connection hole. Another type of conduit connector, termed a clamp connector, consists of a split block bored out to house the unflared ends of a conduit. The conduit is gripped by tightening two clamping bolts, and is located by two bifurcated pins.
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Body
Conduit
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Nipple-Type Connector
Tecalemit Nipple
Conduit Connector Nipple
M7 MAINTENANCE PRACTICES CONTROL CABLES
Cover Plate
Figure 283
Conduit Clamp
Lock Pins
Teleflex Conduit Connectors
Body
Clamp-Type Connector
Clamp Connector Bolts
Conduit Connector
Typical Quick-Break Unit
Interlocking Rods
Conduit
Conduit
Conduit Connector Nipple
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Page: 570
4. Cable. The cable must be kept clean, free from kinks and well lubricated. If dirty, it may be cleaned in kerosine, wiped dry with a non--fluffy cloth and re lubricated. A cable that has been damaged, strained or over heated, must be renewed. The method of fitting a new cable is as follows: A. Assemble the conduit in position. B. Cut the cable 2 inches in excess of requirements. C. Fit the cable into the unit and engage with the transmitting end fitting. D. Assemble the receiving end fitting and mark the required length of cable. E. Remove the cable from the conduit and cut to length. F. Replace the cable and, at the same time, smear the cable with high altitude grease as it enters the conduit. G. Connect the cable to the end fittings and check for freedom of movement and range of movement. H. Ensure that all fittings are in safety and correctly locked. Lubricate, as necessary. 5. Sliding End Fitting. To attach the cable to a sliding end fitting, unscrew the hexagon plug, screw the locknut right back and pass the cable through the plug, then proceed as follows: A. Screw the lock spring on to the end of the cable, so that about 3/16 in (two threads) of cable projects through the spring. B. Insert the cable end, with its lock spring, into the bore of the end fitting and screw the plug tight down. During this operation the end fitting must be prevented from rotating. C. Check that the free end of the cable is beyond the inspection hole, but not beyond the fork gap (fork end fittings only). If satisfactory, position the tab washer, tighten the locknut and lock with the tab washer. D. Check the distance from the face of the bore to the sliding tube which should not exceed 0.45 inches. This ensures that the lock spring is tightly compressed.
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Teleflex System Installation 1. Conduit. Rigid conduit must be clean, free from dents and deformations and reasonably straight. When renewing a conduit, never use conduit that has been previously bent for some other part of the system. After fitting the cable in the conduit, it should be possible to work the cable backwards and forwards by hand. If this is not possible, the run of conduit has not been installed properly. Damage to rigid conduit may be repaired by inserting a new length of conduit and making the connection by use of a connector. Bending, if necessary, should be done by use of a bending machine, or by using a special hand bender. Flexible conduit, if damaged, must be completely renewed. 2. Conduit Connectors. When tightening a nipple type connector, two spanners should be used to prevent twisting of the conduit. If there is any end play between the conduit and the body of the connector after tightening, dismantle the connection and check the flare on the conduit; flaring of a conduit should be done only with the special flaring tool provided. When fitting a clamp type connector, the ends of the two lengths of conduit must be square and unflared. To fit the connector, remove the locking pins and slacken off the clamping bolts. Slide the two lengths of conduit into the connector and ensure that the ends butt centrally in the transverse slot, then tighten up the clamping bolts. Insert a drill of the correct size through the locking pin holes. Operate the drill which will cut half way through the wall of the conduit. Insert the bifurcated locking pins and open out their legs. The correct size drill is 3/32 in dia for No. 2 and No. 3 conduits. 3. Wheel Units. To fit the cable into the single entry unit, tuck it into the slot in the gear wheel and ensure that the cable helix engages with the gear wheel teeth to give a wrap of at least 40o. On double entry units, the cable should engage with the gear wheel correctly and project through the lead out hole throughout the travel of the control. Ensure that the cable end, when fully extended, does not foul the blanked end of the spent travel tube. All wheel units should be packed with high altitude grease.
M7 MAINTENANCE PRACTICES CONTROL CABLES
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Lockspring
M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 284
Tabwasher
Swivel Tube
Outer Sliding Tube
Assembly of Teleflex Sliding End Fitting
Forked-End Type
Plug Permanently Secured to Tube
Locknut
Inspection Hole
Cable
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Hand Lever A typical hand lever is illustrated. If it is necessary to dismantle an existing control or to fit a new cable, unscrew the adjustment to slacken the cable, then rotate the nipple and slide the nipple and cable sideways to pass the cable through the end fitting slot.
End Fittings Various types of end fitting and connector are provided, each installation being designed to meet a specific requirement. Normally, the transmitting end of a control is fitted with a hand lever which engages with the nipple on one end of the cable. At the remote end, the cable passes through an adjustable stop and is connected to the component operating lever. To return the hand lever to the normal position after operation, the system is spring loaded either at the transmitting or receiving end of the control run.
Cable Nipples When a control assembly is made up, the ends of the cable are threaded through brass nipples which are soldered or swaged to the cable.
Conduit The conduit consists of a close coil wire, covered with cotton braiding and finished with a black waterproof coating. Caps are fitted on each end of the conduit to prevent the braiding from unravelling and to reinforce the end of the conduit. On some installations, rigid conduit is used to house the cable over straight runs.
Cable This short run, lightly--loaded type of control has a cable made of non corrodible steel wire, which. is designed for ”pull” operation only. The return action is provided by a spring. This is the sort of cable that is used for operating the brake cable on push bikes
BOWDEN CONTROLS
M7 MAINTENANCE PRACTICES CONTROL CABLES
Page: 572
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Cap
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Stop
Nipple Cable Cap Conduit
Hand Lever
Spherical
Bowden Control Components 1
Typical Hand Lever
Parking Catch
Spade Grip
Cable
Coiled Wire
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Figure 285
Cable and Conduit
Cotton Braiding
M7 MAINTENANCE PRACTICES CONTROL CABLES
Types of Nipple
Trunnion Plain
Page: 573
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Junction Box A junction box is used for connecting a single cable to two others where there are two components to be operated by a single control or where one component is operated by two controls.
Connectors Two types of connector are used. The cable connector is used for joining two cables only and cannot be employed where a conduit is fitted. It is also used for joining a length of Bowden cable to a cable of a different type, such as may be used for long straight runs. The control connector is used for joining two Bowden controls, as illustrated.
Adjustment Stop The remote end of the cable usually passes through a plain stop and is attached to the component by the cable nipple. The plain stops, which may be fitted to both ends of the conduit, consist of hexagon headed screws drilled to allow the cable to pass through. The head of each screw is counterbored to receive the protective cap fitted over the end of the conduit. When the stop is fitted to the remote end of the conduit, it is mounted in a Tee barrel, which must be securely fixed to a rigid member of the airframe. Where it is inconvenient to fit plain stops at the ends of the conduit, a double ended stop may be fitted in the length of the conduit. The stops also enable the length of the conduit to be adjusted, thus altering the tension of the cable.
M7 MAINTENANCE PRACTICES CONTROL CABLES
Page: 574
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Locknut
Tee-Barrel
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Typical Junction Box
One cable entering operates two cables leaving (for spring-return controls)
Adjustable Stop and Tee-Barrel
Adjustment Stop
M7 MAINTENANCE PRACTICES CONTROL CABLES
Figure 286
Safety Hole
Control Connector
Cable Connector
Double-Ended Stop
Note: thread of adjustment end must cover safety hole
Bowden Control Components 2
Cable
Barrel Connecting Conduits
Locknut
Adjustment End
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Conduit
Cable
Page: 575
Conduit
Cap
Slider Connecting Cables
Cap
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Page: 576
4. Renewing a Control. When a cable or conduit is to be renewed, the faulty component should be used as a guide to the length required for the new part. The conduit may be cut to the exact length required, but it is advisable to leave the cable rather longer than necessary, because it simplifies the fitting of the cable. The method of fitting a new cable is as follows: A. a nipple to one end of the cable. Lubricate the cable. B. Thread the adjustable stop over the cable and slide on the conduit making sure that the protective caps are fitted at each end. If required, thread on a second adjustment stop. C. Fix the control temporarily in position on the aircraft along the route it is to follow. D. Make sure that the stops are at their minimum length and that the part to be operated is in the normal position, then slide the other nipple on to the cable. Pull the cable taut and, with a lead pencil, mark off the correct position for the nipple. E. the control from the aircraft, cut the cable to length and solder the second nipple in position. F. Fix the control correctly in the aircraft. Adjust the stops until all slack in the cable is taken up and then tighten the locknuts.
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Installation 1. Conduit.The conduit must be clean, free from kinks or distortion and not damaged. If damaged, the conduit must be renewed. Any bends in the conduit should be as large as possible. The minimum radius of bend is twelve times the diameter of the conduit. Where the cable is connected to a lever, the alignment should be such that the centre line of the conduit is in a straight line through the mid position of the rise and fall of the arc of travel of the lever. If this adjustment is not made, the cable may rub on the edge of the stop and be worn away. When the conduit has been correctly aligned, the Tee barrel forming the adjustable stop mounting must be securely locked in this position. This is important as, should the Tee barrel swivel, the control will be distorted. The control should be attached to the airframe by pliable clips. For controls longer than 2 ft., the conduit should be supported every 12 in. The conduit of a Bowden control should never be in tension. 2. Cable. Care must be taken when handling the cable to avoid kinking it, as this will cause the cable to work harshly in the conduit. The cable must be clean, free from fraying or corrosion and lubricated with graphited synthetic grease applied at room temperature (60-70oF.) The grease must be well rubbed into the interstices of the cable. 3. Servicing. The control should be inspected periodically as follows: A. Inspect the cable ends for fraying or other damage. Frayed cables must be renewed. B. Inspect the conduit for kinks and signs of wear, especially at bends and at the ends. C. If there is any slackness in the cable, screw out the conduit adjustment stops until the slackness disappears. After adjustment, make sure that all components are still in safety and securely locked. D. Operate the control lever over its full range and ensure that the spring returns the lever freely and smoothly to its stop. E. Check the security and locking of mountings and clips.
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M 7.17 AIRCRAFT HANDLING AND STORAGE
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 287
Taxiing
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Towing In general when an aircraft is towed on firm level ground it will be via a towing arm attached to either nose or tail wheel. If the aircraft is on soft ground, then a towing bridle is used which is attached to both main wheels, whilst the aircraft is steered using a towing arm attached to the nose or tail wheel. When towing tailwheeled aircraft on soft ground they should be towed forward whilst nose wheeled aircraft can be towed forward or backward. Checks that should be carried out during towing operations include: S Ensure undercarriage is locked and has ground locks fitted S Ensure brake system is serviceable and has sufficient reserve pressure to operate the brakes. The braking system should also be checked when first moving the aircraft. S Tyres are correctly inflated. S Ensure the correct number of personnel are available, this includes a supervisor in overall charge of the tow and lookouts at the extremities of the aircraft who are in constant contact with the suprvisor. S There must be a qualified operator to operate the brakes from the flightdeck who is in contact with the tow supervisor at all times. S Where necessary, ensure nosewheel steering is disconnected/disengaged. S The tug driver should be fully qualified and take orders only from the towing supervisor. S Navigation light must be swithched on. S Permission to tow must be obtained from ATC prior to towing. S On completion of the tow, ensure the landing gear is pointing straight ahead and has turned at least one full turn in order to relieve stresses on the landing gear and tyres.
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Page: 579
On completion of the tow the aircraft should be parked up observing the following precautions: S The aircraft should be parked so that it doesn’t interfere with the movement of other airfield traffic. S Park into wind wherever possible. S Covers blanks and locks should be fitted as required. S Wheels should be chocked fore and aft. S doors and hatches should be secured.
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General An aircraft may be moved under it’s own power, manually, using a tug or tractor and finally by using hand operated self powered trolleys.
TAXIING AND TOWING
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 288
Towing via Nose Landing Gear
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Page: 580
M7.17 (Cat A)
IR PART 66
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IT IS RECOMMENDED THAT A TOWBAR WITH A DAMPING SYSTEM IS USED.
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You can use the nose landing gear tow--bar fitting to tow or push the aircraft: S with maximum weight, S with the engines between zero and idle.
Speed imits, when the passenger/crew doors are fully open and locked and/or cargo doors open in vertical position: S the permitted maximum speed is 10 km/h (6.21 mph).
Speed limits, when the door is closed and locked or removed: S for a tractor with a tow bar, a maximum speed of 25 km/h (15.5 mph) is permitted S for a tractor without a tow bar (ie using a lifting device), a maximum speed of 32 km/h (19.8 mph) is permitted.
You can use the MLG attachments to tow the aircraft: S with the engines shut down, S when the aircraft is bogged down.
NOTE: NOTE:
NOTE:
M7.17 (Cat A)
IR PART 66
Page: 581
THE ENGINE THRUST RESISTANCE AT GROUND IDLE IS 400 DAN (FOR EACH ENGINE IN OPERATION). USE THESE COEFFICIENTS FOR THE FRICTION BETWEEN THE TYRES OF THE TOW TRACTOR AND THE GROUND, I.E. DRY CONCRETE OR ASPHALT : 0.80 WET ASPHALT : 0.75
IN ALL CALCULATIONS FOR MTW (MAXIMUM TAXI WEIGHT), WHEN THE AIRCRAFT IS PUSHED REARWARDS WITH THE ENGINES AT IDLE, THRUST RESISTANCE MUST BE ADDED TO THE TOWING LOADS.
Approximate Towing Load
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Towing During maintenance work, the aircraft is normally moved and steered by a tractor attached to the nosewheel axle via a towbar. When towing in a limited space, it is essential that the aircraft does not turn on a locked wheel, since this can result in deformation and excessive wear of the tyres.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 289
Towing via Main Landing Gear
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M7.17 (Cat A)
IR PART 66
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DURING TAXIING/TOWING OPERATIONS (INCLUDING LOW SPEED OPERATIONS), EACH PERSON IN THE AIRCRAFT MUST BE IN A SEAT WITH THE SEAT-BELT FASTENED. IF THE SEAT-BELT IS UNFASTENED, THERE IS A RISK OF INJURY IF THE AIRCRAFT STOPS SUDDENLY.
2. ENSURE THAT NO OBJECTS (FOD) CAN BE BLOWN AWAY OR INGESTED BY THE ENGINES.
1. ENSURE THAT, WHEN THE AIRCRAFT MOVES UNDER ITS OWN POWER ON THE GROUND, NO-ONE ENTERS AN AREA WHERE THE AIRCRAFT CAN CAUSE INJURY OR EVEN DEATH.
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Marshalling signals The person taxiing an aircraft should obey all marshalling signals, but has final decision on whether to take notice of the signal or not. The marshaller is responsible for providing the aircaft flight deck with signals that will allow the aircraft to manoeuvre safely.
WARNING:
Taxiing The aircraft is normally taxied with all engines running, but in exceptional circumstances may be taxied on one engine. The nose wheels are steered hydraulically via the nosewheel steering system, which is controlled by a hand wheel (tiller) in the cockpit to a maximum steering angle (depending on the aircraft type) of +/- 70o. If nosewheel steering is not available, the aircraft may be steered by differential use of LH and RH landing gear wheel brakes.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Page: 583
M7.17 (Cat A)
IR PART 66
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Chocks Removed
Chocks Inserted
Start Engine
Slow down engine on indicated side
Cut Engines
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 290
Stop
Brakes On
Move Ahead
Turn Right
Turn Left
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Slow Down
Proceed to next Marshaller
This way
Negative
Affirmative
M7.17 (Cat A)
IR PART 66
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 291
Lifting and Shoring
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M7.17 (Cat A)
IR PART 66
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Aircraft Jacks Aircraft jacks are usually hydraulically operated and are used to raise and lower the aircraft.If the aircraft is to be raised for long periods, then trestles are used in conjunction with the jack There are four types of jack: S Bottle jack -- Used for wheel changes. S Bipod -- One of the legs of a quadrupod jack is removed to leave two load bearing legs and one adjustable support leg. This is used for arc lifts. This is a difficult operation and is not often carried out. S Tripod -- Three legs, equally disposed. Used for vertical lifts. S Quadrupod -- Four legs, equally disposed. Two fixed and two adjustable to allow for uneven ground. Hydraulic jacks can range in height from about 3 feet (1 m) to about 15 feet (5m). Some of the larger jacks may have an operating platform part way up the main body reached by a fixed step ladder. Hydraulic jacks comprise a basic central hydraulic unit around which are the support legs. The moving pillar has either a screw thread and locking collar or a collar and locking pin which enables the jack to be mechanically locked when the aircraft is at the correct height. This prevents the collapse of the jack due to fluid leakage. To release the locking device the jack must be raised slightly to off--load the collar. Raising the jack is by means of a pump after the fluid control valve has been closed. Some jacks may be powered pneumatically and controlled from a central control panel. The air release valve must be opened whenever the jack is raised or lowered.
M7.17 (Cat A)
IR PART 66
Page: 586
Shoring An aircraft on jacks is subjected to structural stresses. Shoring is necessary to give support to the wings in order to release loads on the structure before modifications or major repair work can be carried out.
To lower the jack, release the locking collar and slowly open the oil control valve to control the speed of fall. The air release valve must be closed when the jack is stationaryand the oil--control valve must remain closed--when the locking device is engaged. An adapter is fitted into the top of the pillar and this locates into a jack plate or pad which is fitted, usually by pip pins, onto the underside of the airframe (check location in the AMM and painted on the airframe). The adapter and plate form a ball joint which gives a degree of flexibility when raising and lowering the aircraft. The bottom of the legs of the jack fit into plates with a ball socket joint to allow for uneven ground. It is essential that the plates sit firmly on the ground and that the legs are aligned with a small recess in the plate socket to prevent binding. When jacking ensure all legs are adjusted so that they carry equal weight, pins are fully in, and that the jack is vertical (some have a spirit level fitted). The lifting of an individual landing gear strut is accomplished using a landing gear jack positioned under a jack point integral with the base of each strut. No special provision for aircraft shoring is necessary beyond the lifting of the aircraft with hydraulic jacks and the installation of a rear fuselage support (tail steady) to steady the aircraft. Lifting for aircraft recovery is by standard recovery methods using lifting airbags.
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Lifting and Shoring Aircraft need to be supported clear of the ground for maintenance purposes and this is usually achieved using jacks and trestles Aircraft lifting is generally accomplished using three hydraulic jacks; one positioned under the front fuselage and one under each wing. An auxiliary jack may be provided on each side of the centre fuselage.
JACKING, TRESTLING AND SHORING
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 292
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M7.17 (Cat A)
IR PART 66
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Lifting practices Whenever possible, jacking procedures should be carried out on a site protected from the wind, preferably in a hangar. When jacking in the open, the aircraft must be headed into wind.
ENSURE THAT ALL SERVICING EQUIPMENT IS CLEAR OF THE AIRCRAFT DURING LIFTING AND LOWERING PROCEDURES.
CAUTION:
Page: 588
THE AIRCRAFT MUST ONLY BE JACKED ON A LEVEL SURFACE KNOWN TO BE CAPABLE OF SUPPORTING EACH JACK.
ENSURE THAT ALL CRITICAL STRESS PANELS ARE FITTED PRIOR TO JACKING THE AIRCRAFT TO AVOID DAMAGING THE AIRFRAME.
CHECK THAT PERSONNEL HAVE BEEN CLEARED FROM INSIDE THE AIRCRAFT AND THAT ALL PERSONNEL IN THE VICINITY OF THE AIRCRAFT HAVE BEEN INFORMED OF THE PROCEDURE IN PROGRESS.
BEFORE COMMENCEMENT OF JACKING PROCEDURES, ENSURE THAT THE LANDING GEAR LEVER IS IN THE DOWN POSITION AND THAT ALL LANDING GEAR LOCKS ARE FITTED.
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WARNING:
WARNING:
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Lifting A complete aircraft, or an individual landing gear strut and its wheel assembly is lifted clear of the ground using hydraulic jacks. Three main jack points are provided on the aircraft primary structure to accommodate aircraft lifting jacks. One is situated immediately forward of the nose landing gear compartment and one under each wing outboard of the main landing gear struts. The jack points provide threaded receptacles for the attachment of removable jack adaptors. Two auxiliary jack points may be provided on the primary structure on each side of the centre fuselage and may be used as an alternative to the main jack points if maintenance requires it. A rear fuselage support is positioned under a specific station (depending on the aircraft type) to steady the aircraft during maintenance procedures whilst the aircraft is on jacks. Auxiliary steps are used to provide access to the passenger stairs when the aircraft is on jacks.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Jacking Point
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 293
Jacking Point
Jacking Point
Jacking
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Safety Jack
Page: 589
M7.17 (Cat A)
IR PART 66
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THE PROCEDURE FOR LOWERING A LANDING GEAR STRUT IS THE REVERSE OF LIFTING.
Chock the two other wheels (when lifting one landing gear strut) Ensure aircraft parking brake is off Position landing gear jack under jack point on base of strut Operate jack until wheels are lifted just clear of ground.
NOTE:
S S S S
Lifting on landing gear struts using bottle jack A jack point is provided on all three landing gear struts to accommodate the landing gear hydraulic jack. Any strut and its wheel assembly can be individually lifted clear of the ground for maintenance procedures such as wheel or brake change. If both tyres on one landing gear strut are deflated, there is insufficient clearance to insert the landing gear jack under the base of the strut. If, in this case, it is impractical to lift the aircraft using the main jacks, a landing gear ramp can be positioned in front of the affected wheels and the aircraft towed onto the ramp to give the required clearance for landing gear jack insertion.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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IR PART 66
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 294
Landing Gear Jacking Points
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IR PART 66
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ALL GUIDE--LINES ARE FOR AIRCRAFT PARKING IN NORMAL WEATHER CONDITIONS.
BEFORE YOU CAN DO THIS PARKING PROCEDURE AGAIN,THE AIRCRAFT MUST FIRST DO A FULL FLIGHT CYCLE.
YOU MUST CONTINUE TO DO THE SCHEDULED MAINTENANCE DURING THE PARKING PERIOD.
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Safety Precautions S Park the aircraft on a flat surface, ensuring that the wheel of the nose landing gear is on the aircraft axis and the aircraft points into the wind S Install safety devices on the landing gears S Make sure that the flaps, slats, spoilers and thrust reversers are retracted S Make sure that the THS is set to neutral S Put the wheel chocks in position: -- NLG: -- in front of and behind the wheels -- MLG: -- in front of the FWD wheels and behind the AFT wheels S Ground the aircraft.
S If the aircraft is parked in high wind conditions, check the aircraft stability and moor the aircraft if necessary. S If the aircraft is parked in cold weather conditions, do the cold weather maintenance procedures.
NOTE:
CAUTION:
M7.17 (Cat A)
IR PART 66
Page: 592
Close--Up S Make an entry in the aircraft log book or attach a tag on the captain’s sidestick to inform the crew that protection covers/devices are installed S Remove the ground support and maintenance equipment, the special and standard tools and all other items S Make sure that you close all access/doors.
Aircraft Maintenance Configuration S Push the DITCHING push button switch to close the avionics ventilation skin valves S Make sure that the windows of the cockpit are closed.
Installation of Protection Devices on Engines Protection of: S engine air intakes S engine exhaust nozzles and the centre plug openings S engine air inlet scoop.
Installation of Protection Devices on APU Area Protection of: S APU exhaust duct S outlet duct of the APU oil cooler.
Installation of Protection Devices on the Fuselage Protection of: S total temperature sensors S pitot probes S angle--of--attack sensors S static probes.
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Parking Procedure (of not more than 2 days): ensures preservation for a parking period of not more than 2 days.
PARKING
A/C STORAGE METHODS
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Figure 295
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Examples of Protection Devices on Fuselage
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M7.17 (Cat A)
IR PART 66
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ENSURE THAT THE AVIONICS VENTILATION CONTINUES TO OPERATE CORRECTLY.
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Ensure that there are no leaks from: S the wings S the lower fuselage S the landing gears S the engines S the APU S the horizontal and vertical stabilizer.
General Visual Inspection of Airframe from Ground for Correct Condition
Remove Cover Slips from S total temperature sensors S pitot probes S angle--of--attack sensors S static probes.
Removal of Protective Equipment S APU exhaust plug S APU oil cooler outlet plug S Engine inlet cowl cover S Engine inlet scoop cover.
NOTE:
Open the avionics ventilation skin valves.
Aircraft Configuration
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IR PART 66
Page: 594
Remove the ground support and maintenance equipment, the special and standard tools and all other items.
Remove tag from the captain side-stick or write in the log book that the protection covers/devices are no longer installed.
Remove the wheel chocks from the main and nose landing gears.
Remove ground cables from the aircraft.
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RETURN TO OPERATION (PARKING OF NOT MORE THAN 2 DAYS)
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Figure 296
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Parking Intervals (Not More Than 2 Days)
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IT IS RECOMMENDED THAT THERE IS NO CANNIBALIZATION OR REMOVAL OF PARTS DURING THIS PARKING PERIOD.
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Protection of the Water and Toilet System Potable water system S Ensure the system is empty and dry. If necessary, drain, flush and dry the system. Toilet system S Ensure that the system is empty. If necessary, drain, flush and use disinfectant to clean the system.
YOU CAN IGNORE THIS STEP IF THE LAST FLIGHT CYCLE WAS IN THE LAST 24 HOURS (ENGINES AND APU OPERATED). IN THESE CONDITIONS, THE PARKING PERIOD STARTS FROM THE END OF THIS LAST FLIGHT CYCLE. S Operate the APU for at least 5 min. at no-load governed speed S Run the engines and let them become stable at ground idle for 15-20 mins S Do a thrust reverser full cycle
NOTE:
Protection of the Engines and APU
Aircraft Configuration Ensure that the fuel tanks are 90% full (minimum).Over 30 days tanks must be full
NOTE:
M7.17 (Cat A)
IR PART 66
Page: 596
Put aircraft in parking configuration. Ensure that all the external structural drain holes are not clogged. Ensure that all the engine drains are not clogged. Carry out full parking procedure. Seal the air conditioning /ventilation inlets and outlets with STORAGE PRESERVATION Material No.15--002 and adhesive tape. Put tarpaulins on the MLG wheels.
Protection of the Doors S Open all doors including -- the passenger/crew doors -- the emergency exit doors -- the cargo compartment doors -- the landing gear doors -- all other the pressurized access doors and S apply SPECIAL MATERIALS Material No.05--043 on seals of all the doors S Close all doors.
Protection of the Electrical System S Remove or disconnect the batteries.
Protection of the Seats S It is recommended to do the protection of the cockpit and passenger seats with STORAGE PRESERVATION Material No.15--002.This is to prevent discolouration by the sun during a long parking period.
Protection of the Fuel System S Drain water from all the fuel tanks. You must wait for one hour after refuelling is completed before you do the water drain procedure.
Protection of the Air Data System S Flush the total pressure line of the Air Data Module S Flush the static pressure line of the Air Data Module S Drain and flush the standby static and standby total pressure lines of the Air Data Module
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Parking Procedure (of not more than 12 Weeks): ensures preservation for a parking period of not more than 12 weeks. It keeps the aircraft in Flight--Ready condition. Periodic Ground Checks must be carried out at 7--day and 15--day intervals. S If the aircraft is parked in high wind conditions, check the aircraft stability and moor the aircraft if necessary. S If the aircraft is parked in cold weather conditions, do the cold weather maintenance procedures.
PARKING
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 297
Protection Devices on Engine
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IR PART 66
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Periodic Ground Check (at 15--day intervals) Procedure Do a general visual inspection of the airframe from the ground for condition. S Ensure that there are no leaks S Ensure that there are no signs of bird nesting in all areas of the aircraft to which birds have access S Check for bird excrement. If present, remove it. S Do a check of the outer skin for unusual contamination. Make sure that the extension of the landing gear shock absorbers is correct. Do a check of the tire pressure. Do a check of the hydraulic reservoir level. Drain water from all the fuel tanks. CAUTION:
Page: 598
MAKE AN ENTRY IN THE AIRCRAFT LOG BOOK OR ATTACH A TAG ON THE CAPTAIN’S SIDE-STICK TO INFORM THE CREW THAT PROTECTION COVERS/DEVICES ARE INSTALLED.
Put the aircraft in parking configuration. Let the engines and the APU become cool and install protection covers/plugs on the fuselage,the engines and the APU area. Record any discrepancy in the log book. Install tarpaulins on the MLG wheels.
Move the aircraft.
Operate Air Conditioning system. Operate all the flight control surfaces on full travel and ensure that they operate correctly. Do the operational test of the bleed air system. Do the operational test of the wing--ice protection system. Do the operational test of the engine air intake ice protection. Do a thrust reverser cycle.
Operate the APU and the Engines S Start the APU S Start the engines with APU bleed and operate them at idle power.
Periodic Ground Check (at 7--day intervals) Check of Aircraft Condition Ensure that the protection covers/plugs are correctly installed. Do a general visual inspection of the airframe from the ground for condition. Make sure that there are no leaks from: S the wings S the lower fuselage S the landing gears S the engines S the APU S the horizontal and vertical stabilizer.
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IR PART 66
System Test S Do the functional test of the nose wheel steering with the handwheel and with the pedals S Do the operational test of the Normal braking system and Alternate braking system.
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Periodic Checks and Return in Operation During the parking period, do the periodic checks: S at 7--day intervals S at 15--day intervals.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Figure 298
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Parking Intervals (not more than 12 weeks)
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M7.17 (Cat A)
IR PART 66
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-- WHILE THE AIRCRAFT IS IN STORAGE, ENSURE THAT YOU DO THE MAINTENANCE CHECKS SPECIFIED FOR STORAGE. BEFORE YOU PUT THE AIRCRAFT BACK INTO SERVICE, IT IS RECOMMENDED THAT YOU MAKE SURE THAT ALL THE CALENDAR TASKS SCHEDULED FOR THE PERIOD DURING WHICH THE AIRCRAFT WAS IN STORAGE ARE COMPLETED (REFER TO THE MAINTENANCE PROGRAM). DO NOT CHANGE OR STOP THE MAINTENANCE PROGRAM WITHOUT APPROVAL FROM YOUR LOCAL AUTHORITIES.
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Protection of the APU S Do the preservation of the APU.
Protection of the Engines S Do the preservation of the engines.
M7.17 (Cat A)
IR PART 66
WHEN YOU USE ADHESIVE TAPE, DISCOLORATION OF THE AIRCRAFT PAINT OR TRANSFER OF COLOURS CAN OCCUR. THIS IS WHY YOU MUST USE THE MINIMUM POSSIBLE ADHESIVE TAPE.
For return-to-service, do the return-to-service procedure.
During the storage period, do the periodic checks: S at 7--day intervals S at 15--day intervals.
Page: 600
Close Access Close all the window shades, emergency exit doors, cargo compartment doors and gear doors. Put the aircraft in the storage area. Do the full parking procedure.
NOTE:
Seal the following areas with STORAGE PRESERVATION Material No.15--002 attached with adhesive tape (record the location): S inlets and outlets of the air conditioning packs S battery venturi S pre-cooler outlets S anti--ice air outlet and the access panels which are on the engine air intakes.
Protection of the Oxygen System S Close the valve of the oxygen cylinder and bleed the oxygen system.
Protection of the Fuel System S Fill all the fuel tanks to 90% of their total capacity and all the fuel system lines S Make the vents wet (so that the sealants will not become dry and will not crack). Operate the water drains one hour after you refuel the tanks.
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Storage Procedure (not more than 1 month) S Clean the aircraft externally and internally S Drain of the potable water system S Drain the toilet system S Open all doors and apply SPECIAL MATERIALS Material No.05--043 to all the seals of the doors S Make sure that there is no blockage in any structural drain holes S Flush the total pressure line and the static pressure line of the Air Data Module S Lubricate the mechanical control chains of the THS S Lubricate all rollers and pinions of slat tracks, all spoiler linkage bearings that have grease nipples and hinge and attachment fittings of horizontal stabilizer S Check tyre pressures S Remove the batteries.
CAUTION:
STORAGE
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Aircraft Storage - Inspection Intervals
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Figure 299
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Page: 601
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IR PART 66
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Drains Visually inspect the drains.
Hydraulics S Depressurize the hydraulic systems -- Put a warning notice in position to tell persons not to operate the systems during the aircraft storage procedure S Do a check of the hydraulic components for external leakage S Apply SPECIAL MATERIALS (Material No.05--005) on: -- all the hydraulic unions in the wheel wells -- the bolt heads of the hydraulic reservoirs -- the pipe clamps -- the trailing edge of the wing S Apply SPECIAL MATERIALS on the solenoids of the hydraulic flap manifold S Inspect the flight controls S Check the oil level of the flap PCU and slat PCU gearbox.
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IR PART 66
Tyre Storage (for a period > 2 months) It is recommended to install old tyres or wheels with old tyres.
Tyre Storage (for a period < 2 months) Check the inflation pressure.
Page: 602
Landing Gear S Apply COMMON GREASE to: -- the sliding tube of the shock absorber, the actuator rods and the uplock mechanism. S Apply talcum to all the rubber parts but not the tyres S Ensure that there is no corrosion on the brakes and on each half wheel.
Protection S Apply SPECIAL MATERIALS to all the seals of the doors S carry out protection of all the light-alloy areas that are unpainted S Apply SPECIAL MATERIALS or COMMON GREASE to the steel parts that are unpainted and on the mechanical rods in unpressurized areas S Apply SPECIAL MATERIALS (Material No.05--027) to: -- the cases, electrical connectors, solenoids, brackets, screw- and boltheads located in the APU compartment -- in all the holes, especially in the areas where condensation can occur.
Lubrication S Lubricate the mechanical control chains of the THS, all the rollers and pinions of the slat tracks, spoilers, linkage bearings, cargo compartment doors, passenger/crew doors and emergency exit doors hinges and the attach fitting of the horizontal stabilizer, rudder bearing and sliding window.
Rain Repellent System De--activate the rain repellent system.
Water Removal Remove the water from the pitot/static lines.
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--WHILE THE AIRCRAFT IS IN STORAGE, ENSURE THAT YOU DO THE MAINTENANCE CHECKS SPECIFIED FOR STORAGE. BEFORE YOU PUT THE AIRCRAFT BACK INTO SERVICE, IT IS RECOMMENDED THAT YOU MAKE SURE THAT ALL THE CALENDAR TASKS SCHEDULED FOR THE PERIOD DURING WHICH THE AIRCRAFT WAS IN STORAGE ARE COMPLETED (REFER TO THE MAINTENANCE PROGRAM). DO NOT CHANGE OR STOP THE MAINTENANCE PROGRAM WITHOUT APPROVAL FROM YOUR LOCAL AUTHORITIES.
Clean Clean the aircraft.
CAUTION:
Storage (for a period as long as 2 years)
STORAGE (CONT’D)
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 300
A/C Storage - Inspection Intervals
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IR PART 66
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Protection of the Fuel System S Fill -- all the fuel tanks at 90%of their total capacity -- all the fuel system lines S Make the vents wet (so that the sealants will not become dry and will not crack) S Mix MICROBIOLOGICAL CONTAMIN. PROTECT. MATERIALS with the fuel as a preventive step S Operate the water drains one hour after you refuel the tanks S Check all the fuel tanks for leakage S Apply SPECIAL MATERIALS to the switches on the REFUEL/DEFUEL panel.
Protection of the APU Carry out the preservation of the APU.
Protection of the Engines (for a period of > 1 year) Ref. TASK 72--00--00--600--805.
Protection of the Engines (for a period of 90 days - 1 year)) S Remove the IDG S Carry out the preservation of the engines.
Protection of the Engines (for a period of 0 to 90 days) S Carry out the preservation of the engines.
M7.17 (Cat A)
IR PART 66
Put blanking caps on the disconnected electrical connectors.
Removal of Components Remove the following: S digital flight data recorder S cockpit voice recorder S oxygen cylinder/valve assys S crew portable oxygen--equipment S cabin emergency lights S emergency power--supply units S first aid kits S emergency locator beacon S portable and toilet fire--extinguishing bottles S life vests S escape slide S escape slide/raft S autonomous standby power supply unit S wiper arm and wiper blade S engine fire--extinguishing bottles S cartridges of the engine fire--extinguishing bottles S cartridge of the APU fire--extinguishing bottle S APU fire--extinguishing bottles S cartridge of the cargo fire--extinguishing bottle S cargo fire--extinguishing bottle S batteries
Page: 604
Protection and Lubrication of the Landing Gear S Apply SPECIAL MATERIALS on the electrical components (microswitches, connectors, proximity detectors) S Apply COMMON GREASE to the towing and debogging fittings S Put tarpaulins on the bottom sections of the landing gear (this includes the tyres and brakes).
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S Open the cockpit and cabin window shades S Cover the cockpit and passenger seat with a STORAGE PRESERVATION S Apply BONDING AND ADHESIVE COMPOUNDS on the cockpit and cabin windows.
Protection (for a period of 0 to 2 months)
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Visual Inspection: S Examine all the areas of the aircraft where the birds can access. S Ensure that there are no bird’s nests. /cont’d
Move the aircraft by a 1/4 turn of the wheels, to prevent damage to the tyres and brinelling of the bearings.
Inspection Check List: 15 Days Check
Make sure that there is no leakage under: S the wings S the lower fuselage S the engines S the APU S the horizontal stabilizer S the vertical stabilizer S the landing gears.
Inspection Check List: Weekly Check Visual Inspection: S Examine all the areas of the aircraft where birds can access. Ensure that there are no bird’s nests S Make sure that the covers and the plugs are correctly installed.
Remove the batteries. Disconnect and remove the batteries.
Protection Seal with STORAGE PRESERVATION Material No.15--002 attached with adhesive tape (record the location): S the inlets and outlets of the air conditioning packs S the battery venturi S the precooler outlets S the anti--ice, air outlet and the anti--ice duct access panel (on the engine air intakes) S the scoops. Seal the two spray nozzles with plastic bags or films, fixed on the structure with adhesive tape. Seal all the openings that give access to: S the passenger compartment S the cockpit S the cargo compartment S the APU S the engines S the landing gear with STORAGE PRESERVATION Material No.15--002 attached with adhesive tape.
Put the aircraft in the parking condition. Put the aircraft in the mooring condition.
Close the avionics ventilation extract--valve. Close the overboard extract valve.
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IR PART 66
Close Access Close the passenger/crew doors. Close all the access doors and panels that you opened during the storage procedure.
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Protection of the Water/Waste System S Make sure that the water/waste and potable water systems are empty; dry them with air if necessary S Drain,clean and deodorize the toilets.
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Do the following tests: S operational test of the avionics equipment ventilation system S operational test of the bulk cargo ventilation system S operational test of the ice protection system of the wing S operational test of the ice protection system of the engine air intake
S S S S
Open the passenger/crew doors Open cargo compartments Open all the access doors Apply SPECIAL MATERIALS Material No.05--043 on all the seals of the doors S Make sure that all the doors operate correctly S Bleed the standby air--data system S Operate the air conditioning system to remove moisture through the low--pressure ground connection or through the high--pressure ground connection or with the APU.
Check the condition of the aircraft during the storage period:
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S Check that at least the minimum level of HYDRAULIC FLUIDS is in hydraulic reservoirs S Check for corrosion on hydraulic pipes and unions on the landing gear wells, wings and the stabilizers. cont’d
Inspection of the Hydraulic System:
Inspection of Fuel Tanks: S Drain water from the fuel tanks S If necessary,fill all the fuel tanks at 90%of their total capacity and the fuel system lines S Make the vents wet (so that the sealants will not become dry and will not crack).
S Apply COMMON GREASE Material No.04--011 on: -- the sliding tube of the shock absorber -- the actuator rods -- the uplock mechanism.
S Apply SPECIAL MATERIALS Material No.05--027 in all holes, specially in the areas prone to condensation.
Protection:
S Do a visual inspection of the aircraft for impact by foreign objects, fluid leakages (hydraulic fluid, fuel), missing parts, blockage and corrosion.
Check the condition of the aircraft during the storage period:
Inspection Check List: 3 Months Check
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Ensure that there is no leakage. Ensure that the pressure/extension of the shock absorber is correct. Examine the condition of the wheels of the landing gear. Do a tyre pressure check (the correct pressure is the pressure specified for the aircraft storage weight).
Inspection Check List: 1 Month Check
S S S S
Inspection Check List: 15 Days Check (Cont’d)
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Remove the tool installed during the mooring procedure and the tarpaulins Put the aircraft on jacks Turn the wheels by hand to make sure that there are no defect on bearings Put the aircraft on its wheels.
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operational test of the operation of the engine LP--fuel shut--off valves operational test of the operation of the ailerons and their hydraulic system operational test of the operation of the elevators and their hydraulic system operational test of the operation of the rudder and its hydraulic system operational test of the operation of the flap system operational test of the operation of the spoiler hydraulic system operational test of the slat system operational test of the landing gear doors.
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Put the aircraft back to its Initial Configuration.
Close--up:
S S S S S S S S
Put the aircraft in the mooring condition. Carry out the following:
S S S S
Inspection Check List: 3 Months Check (Cont’d) Inspection of the Landing Gear:
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26--21--41--200--801 26--21--41--200--802
24--21--51--400--801 24--38--51--400--801 24--41--00--861--801 24--41--00--862--801 25--62--41--400--801 26--21--00--720--803
23--71--35--400--801 24--21--00--210--818
(SYSTEM TEST) 23--61--00--200--801
21--26--00--710--803
12--12--29--611--801 12--13--24--612--801 12--13--49--612--801 12--13--80--610--801 12--14--32--614--801 12--21--11--615--801 12--22--32--600--801 12--22--32--600--802 12--32--28--281--801 12--32--28--281--802 21--21--41--000--801 21--21--41--400--801 21--26--00--440--801
May 2004
Check the Resistance from Static Discharger to the base and from the base to the Aircraft Structure Installation of the Cockpit Voice Recorder Check of the Oil Level and Oil--Filter Differential--Pressure Indicator (DPI) Installation of the -- IDG Installation of the Batteries Energize the Aircraft Electrical Circuits De--energize the Aircraft Electrical Circuits Escape Facilities --Installation Check of Engine Fire Extinguishing Distribution Piping for Leakage and Obstruction Weight Check of Fire Extinguisher Bottle Hydrostatic Test of Engine Fire Extinguisher Bottle incl. Check of Pressure Switch Setting
Fill Hydraulic Reservoir IDG Servicing Servicing of the APU Oil Reservoir Drain and Replenish Oil of Starter Replenishment of the Tires External Cleaning Lubrication of Main Gear and Doors Lubrication of the NLG and Doors Drain Water from Tanks Fuel sample. for microbiological contamination Removal of the Forward Filter Element Installation of the Forward Filter Element Reactivation of Avionics Ventilation Overboard Extract Valve (13HQ) Operational Test of the Avionics--Equipment Ventilation System
27--84--00--710--801 28--11--00--600--805
27--54--00--710--801 27--64--00--710--801 27--84--00--210--801
27--54--00--200--801
27--34--00--710--801
27--24--00--710--801
27--14--00--710--801
26--25--00--280--801
26--23--41--400--803 26--23--42--400--801 26--24--00--280--801
26--23--41--280--802
26--23--41--280--801
26--22--41--400--801 26--22--42--400--801 26--23--00--200--803
26--22--41--280--801 26--22--41--280--802
26--22--00--200--801
26--21--41--400--801 26--21--41--400--803
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Return to Service (Storage Period not more than 1 Month) Return to Service (Storage Period Up to 2 Years) To operate an aircraft again after a storage period of as long as 2 years.
RETURN TO SERVICE
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Page: 608
Installation of Engine Fire--Extinguisher Bottle Installation of the Engine Fire--Extinguisher Bottle Cartridge Detailed Visual Inspection of the APU Fire--Extinguishing Distribution--Piping Weight Check of APU Fire--Extinguisher Bottle Hydrostatic Test of APU Fire--Extinguisher Bottle and Check of Pressure Switch Setting Installation of the APU Fire Extinguisher Bottle Installation of APU Fire--Extinguisher Cartridge Detailed Visual Inspection of the Halon Filters, Check Valves and Restrictors of Cargo-Compartment Fire--Extinguishing System Weight Check of the Cargo--Compartment Fire--Extinguisher Bottles Hydrostatic Test of the Cargo--Compartment Fire--Extinguisher Bottles Installation of the Fire--Extinguisher Bottle Installation of the Fire--Extinguisher Cartridges Weight Check of Portable Fire--Extinguisher Bottles and a Visual Check Check of the Extinguishing Agent Pressure by Reading Pressure Gauges of All the Lavatory Waste--Bin Fire--Extinguisher Bottles Operational Test of the Aileron and Hydraulic Actuation Operational Test of the Rudder Servo Control with each Hydraulic System Operational Test of the Elevator and Hydraulic Actuation Visual Inspection of the Flap Transmission Assy Operational Test of the Flap System Operational Test of the Spoilers Visual Inspection of the Slat Transmission Assy, Slat Tracks and Rollers, Pinions and Curved Rack Gears Operational Test of the Slat System Removal of The Microbiological Particles
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38--31--00--720--802 49--00--00--710--801 49--11--11--400--801 51--74--11--300--801 52--10--00--010--801 52--30--00--010--802
35--11--41--400--801 35--30--00--210--801 38--10--00--720--801
32--41--11--400--801 32--41--12--400--801 33--51--11--400--801 33--51--38--400--801 34--11--00--170--801 34--11--00--170--802 34--11--00--170--803
32--41--00--210--802
32--40--00--200--801 32--40--00--210--804
30--45--00--440--801 30--45--52--400--801 31--33--55--400--801 32--11--00--220--801 32--12--00--010--801 32--12--00--410--801 32--21--00--220--801 32--31--00--710--801
28--24--00--710--801 29--00--00--863--801 29--00--00--864--801 29--31--00--200--801 30--11--00--710--801 30--21--00--710--801
May 2004
71--00--00--400--801 71--00--00--720--806 71--00--00--860--802 71--00--00--860--804 72--00--00--600--806
54--50--00--200--801
53--39--00--200--801
53--00--00--200--801
52--30--00--410--802
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Operational Test of LP Fuel Valve Pressurize the Hydraulic Systems Depressurize the Hydraulic Systems Check of the Reservoir Fluid Level Operational Test of Wing Ice--Protection System Operational Test of Engine Air Intake Ice Protection Reactivation of the Rain Repellent System Installation of the Wiper Arm Installation of the Digital Flight Data Recorder Detailed Inspection of Main Gear Structure Open the gear doors for Maintenance Close the gear doors after Maintenance Detailed Inspection of Nose Gear Structure Operational Test of the Normal Extension and Retraction System Inspection/Check of the Brakes Check of Normal and Alternate Brake Manifold Accumulators Nitrogen Charge General Visual Inspection of Tires, Wheels and Brakes (for Hydraulic Leaks) Installation of the MLG Wheel Installation of the NLG Wheel Installation of the Cabin Emergency Light Installation of Emergency Power--Supply Unit Flushing of the Principal Total Pressure Lines Flushing of the Principal Static Pressure Lines Draining and Flushing of the Standby Static and Standby Total Pressure Lines Installation of the Oxygen Cylinder/Valve Assy Check Pressure of Portable Oxygen Cylinder Functional Test of Potable--Water Preselect System Functional Test of the Toilet Assemblies Operational Test of the APU Installation of the Auxiliary Power Unit (APU) Repair of Corroded Areas Opening of the Passenger/Crew Door Opening of the Cargo--Compartment Doors with the Hand Pump
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Closing of the Cargo--Compartment Doors with the Hand Pump Visual Check of the Drain Holes in the Lower Part of the Fuselage at FR1 and FR80 Operational Test of the Drain at the Upper Aft End of the Wing Centre Box Operational Test and General Visual Inspection of the Pylon Drain System Installation of the Engine Power Assurance Check Engine Manual Start Engine Shut--down Depreservation
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Spillage Actions to be taken should there be a spillage of fuel will depend on the size and location, the type of fuel and prevailing weather conditions. S Spillage onto the aircraft structure must be cleared prior to the engines being started. S Minor spillage onto the ground must be cleared and the area allowed to dry prior to any engines being started in the vicinity. S If there is a major spillage, fuel-flow must stop, all personnel evacuated from the area and the Fire Services alerted. S Every attempt must be made to prevent contamination of drains and culverts by damming the area with specialist equipment and using absorbing/ mopping agents designed for the job, which are subsequently disposed of in suitable containers in accordance with local regulations.
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’No Smoking’ signs should be displayed at a minimum distance of 15m (50’) from fuelling equipment and aircraft tank vents. A Fuelling Zone at least 6m (20’) from filling/venting points on both aircraft and fuelling equipment should be established prior to fuelling/defuelling operations. Within this zone S no electrical system should be switched on or off, and only those circuits necessary for the operation should be on. S Strobe lighting must not be on. S There must be no use of naked lights. This includes the engines of equipment/vehicles unless they have been designed for that purpose. S If necessary for the refuelling/defuelling operation, an APU (Auxiliary Power Unit) must be started prior to filler caps being removed or connections made. S GPUs (Ground Power Units) should be as far as practicable from aircraft fuelling points and vents. S Fire extinguishers should be at hand. S The aircraft should be earthed and bonded to fuelling equipment. S After the fuelling operation, bonding should not be removed until hoses have been disconnected and filler caps refitted. S Ground equipment must be moved away from the aircraft to prevent damage as the aircraft settles due to its increased weight. S Fuel bowsers will normally position themselves facing away from the aircraft being refuelled, for rapid emergency evacuation. A clear exit must be maintained. S Aircraft engines must not be operated. S People and vehicles within the fuelling zone must be kept to a minimum. S Fuelling is suspended during electrical storms in the vicinity.
AIRCRAFT REFUELLING/DEFUELLING
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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Figure 301
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Typical Fuelling/Defuelling Safety Zone
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Park or picket aircraft -- leave brakes off.
Drain oil and water traps on pneumatic systems.
Clean, drain and remove any foodstuffs from galleys.
Drain and clean all toilet systems.
Drain drinking (potable) water systems.
Drain oil whilst hot (from piston engines in extreme cold), and drain water traps in Pitot/ static systems.
Allow any ice in intakes, water drains, etc, to melt, drain water then fit covers and plugs.
If aircraft is wet apply anti--freeze liquid to the underside of covers before fitting.
Fit all airframe and engine covers, Pitot/ static plugs, and landing gear locks.
Typical After Flight Checks (See AMM)
Clear the working areas of snow and ice.Keep sand and salt away from working areas and aircraft as much as possible.Ideally keep aircraft in heated hangers as much as possible.
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This ice formation, which is less dense than glaze ice, is an opaque, rough deposit. At ground level it forms in freezing fog conditions and consists of a deposit of ice on the windward side of exposed objects. Rime ice is light and porous and results from the small water drops freezing as individual particles, with little or no spreading. A large amount of air is trapped between the particles.
Rime Ice
Hoar frost occurs on a surface which is at a temperature below the freezing point of the adjacent air and, of course, below freezing point itself. It is formed in clear air when water vapour is converted directly to ice and builds up into a white semi--crystalline coating. Hoar frost is feathery.When hoar frost occurs on aircraft on the ground, the weight of the deposit is unlikely to be serious, but the deposit, if not removed from the airframe, may interfere with the airflow and attainment of flying speed during take--off, the windscreen may be obscured, and the free working of moving parts such as flying control surfaces may be affected.
Hoar frost
Icing on aircraft is caused by a combination of freezing conditions and moisture in the atmosphere. It may also be caused by freezing rain or drizzle. The actual amount depends on surface temperature, surface condition, duration of icing conditions, and the amount of moisture present in the atmosphere.
Ice and Snow Formation on Aircraft
If aircraft does not fly within a certain time (depending on ambient temperature) re--do items 2 and 3 above.
Carry out normal before flight inspection.
Check all heaters -- windscreen -- Pitot -- TAT -- drain masts -- ice detectors -- heater mats etc.
Fill systems and check for leaks. Piston engines are usually filled with pre--heated oil.
Pre--heat engines using blower heaters.
Remove ice and snow from airframe and engines using blower heaters or fluid spray systems (see later chapters in this book).
Remove covers, blanks and locks.
Typical Before Flight Checks (see AMM)
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General Safe operation of aircraft in cold weather conditions raises specific problems. Aircraft downtime and delays in flight schedules caused by cold weather problems can be minimized by a program of preventive cold weather servicing. Procedures for cold weather servicing must be developed by the operator. This servicing must meet their specific requirements based on: S their cold weather experience S available equipment and materials S the climatic conditions existing at their bases This topic contains information defining, developing and implementing cold weather preventative maintenance procedures that will minimize aircraft downtime and improve the safe operating level of aircraft in adverse climatic conditions . The aircraft is in cold-soak configuration when it is parked in cold weather (Outside Air Temperature (OAT) lower than 0oC/32oF) and there is no supply of power to the aircraft (no air-conditioning).
DE-ICING AND ANTI-ICING
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It is evident that if ice is deposited on the aircraft, one or more of the following effects may occur: S Decrease in Lift. This may occur due to change in wing section, resulting in loss of streamlined flow.
Conclusions
Normally, snow falling on an aircraft does not adhere, but will settle on the top surfaces only. If the temperature of the airframe is below freezing point however, glaze ice may form from the moisture in the snow. The icing of the aircraft in such conditions, however, is primarily due to water drops, though snow may subsequently be embedded in the ice so formed.
Pack Snow
This is caused by slush/snow/moisture being throne/blown onto the aircraft by the wind, or passing vehicular traffic or blown by propeller/jet efflux from other aircraft.
Debris Ice
Ice formed in this way is dense, tough and sticks closely to the surface. It cannot easily be shaken off and, if it breaks off at all, it comes away in lumps of an appreciable and sometimes dangerous size. The main danger of glaze ice is still aerodynamic, but to this must be added, that due to the weight of ice, unequal wing loading and propeller blade vibration may occur. Also there is the possibility of ice debris damage in flight. Glaze ice is the most severe and the most dangerous form of ice formation on aircraft.
Glaze ice is the glassy deposit that forms over the village pond after a frosty night. On aircraft, glaze ice forms when the aircraft encounters freezing rain with the air temperature and the temperature of the airframe below freezing point. It consists of a transparent or opaque coating of ice with a glassy surface and results from the liquid water flowing over the airframe before freezing; glaze ice may be mixed with sleet or snow.
Glaze Ice
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S Increase in Drag. Drag will increase due to the rough surface, especially if the formation is rime ice -- This condition results in a greatly increased skin friction. S Decrease in propeller efficiency. With turbo--prop and piston engines, the efficiency of the propeller will decrease due to alterations of the blade profile and increased blade thickness, S Propeller vibration due to uneven weight of ice. S Loss of Control. Loss of control may occur due to ice preventing movement of control surfaces. S Increased risk of control surface flutter due to control surface C of G change because of the ice. S Increased Load and Wing Loading. The weight of the ice may prevent the aircraft from taking--off. S Reduced stalling speed. S Loss of Inherent Stability. Loss of the inherent stability may occur due to displacement of the centre of gravity caused by the weight of the ice. S Loss of Vision. This will happen if the windscreen becomes iced over. S Ice debris damage. S Malfunction of Flight/ Engine Instruments. This would occur if Pitot/static and EPR probes/vents became blocked.
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Aircraft in flight may experience rime icing when flying through clouds with the air temperature and the temperature of the airframe below freezing point. The icing extends along the leading edge but does not extend back along the chord. Ice of this type usually has no great weight, but the danger of rime is that it will interfere with the airflow over wings, etc, and may choke the orifices of the carburettor, air intake and flying instruments.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 302
Anti-Icing 1
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Holdover time is the estimated time during which anti--icing fluids will prevent the formation of frost or ice and snow accumulation on the protected surfaces of the aircraft. The holdover time starts at the beginning of the anti--icing treatment.
Anti-icing Anti--icing is a precautionary procedure which provides protection against the formation of frost or ice and snow accumulation on the treated surfaces of the aircraft for a limited period of time (the holdover time). Anti--icing fluids are normally applied cold directly onto clean aircraft surfaces. Typical anti--icing fluids are : S Newtonian fluids (ISO- SAE- or AEA- Type I). Newtonian Fluids (Type I) have a low viscosity that only changes with temperature. S Mixtures of water and Type I fluid S Non--Newtonian fluids (ISO- SAE- or AEA-Type II or Type IV). Non--Newtonian Fluids (Type II or Type IV) have a viscosity that reduces with increased air flow over the fluid. S Mixtures of water and Type II or Type IV fluid.
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Two step De--/Anti--Icing, as inferred, comprises two completely separate steps: 1. De--ice the aircraft (remove frost, ice, slush and snow accumulations). 2. Follow this immediately with an anti--icing procedure.
One step De--/Anti--icing is carried out with an anti--icing fluid, normally heated. The aircraft is de--iced and the fluid that remains on the aircraft gives limited anti--ice protection.
De-icing and Anti-icing De--/Anti--icing is a combination of de--icing and anti--icing procedures and is performed in one or two steps.
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De-icing De--icing is a procedure to remove frost, ice, snow and slush from the aircraft surfaces. De--icing fluids are normally applied heated. Typical de--icing fluids are : S Heated water S Newtonian fluids (ISO- SAE- or AEA-Type I) S Mixtures of water and Type I fluid S Non--Newtonian fluid (ISO- SAE- or AEA-Type II or Type IV fluid) S Mixtures of water and Type II or Type IV fluid.
M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
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M7 MAINTENANCE PRACTICES AIRCRAFT HANDLING AND STORAGE
Figure 303
Anti Icing 2
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A FROST LAYER LESS THAN 3MM (1/8 IN) ON THE UNDERSIDE OF THE WING (DEPENDING ON THE AIRCRAFT TYPE) IN THE FUEL TANK AREA IS PERMITTED WITHOUT EFFECT ON TAKE-OFF PERFORMANCE IF IT IS CAUSED BY COLD FUEL (LOW FUEL TEMPERATURE, OAT HIGHER THAN FREEZING AND HIGH HUMIDITY).
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Fluid Dilution Type I, Type II and Type IV de-/anti-icing fluids can be diluted with water. This may be done if, due to weather conditions, there is no requirement for a long conservation time, or the higher freezing points are sufficient for the present climatic conditions.
A pre--flight inspection of the aircraft must cover all parts of the aircraft. This visual inspection must be done from a position which gives a clear view of all surfaces. Because accumulations of clear ice are sometimes not easily visible, it is recommended that critical surfaces (wings, vertical and horizontal stabilizers and rudder) are inspected by hand. Weather conditions determine when the aircraft de--/anti--icing must be carried out. During checks on the ground, electrical or mechanical ice detectors must not replace physical checks. If the aircraft arrives at the gate with the flaps/slats in a position other than fully retracted, they must be inspected and, if necessary, de--iced before retraction.
NOTE:
M7.17 (Cat A)
IR PART 66
NOTE:
Page: 617
TYPE II OR TYPE IV FLUIDS HAVE A LONGER HOLDOVER TIME THAN TYPE I FLUID.
De-/Anti-icing Fluid Type I, II and IV Type I fluids are normally used for aircraft de--icing and have only a limited effect when used for anti--icing purposes. Type I fluids are normally used for aircraft de--icing. These fluids contain at least 80% by volume of either : S Monoethylene--glycol S Diethylene--glycol S Monopropylene--glycol S or a mixture of the above. The other 20% comprise inhibitors to restrict corrosion and increase the flash--point, together with water and wetting agents. These fluids show a low viscosity which only changes with temperature. The freezing point of a water/glycol mixture will vary with the amount of water contained in the fluid. It should be noted that the lowest freezing point of concentrated TYPE I fluid is approximately --10oC (14oF), whereas the lowest temperature protection will be found with a 60/40 mixture of TYPE I fluid and water, whose freezing point will be below --50oC (-58oF). However, due to the lower viscosity, it flows off the wing more easily. Therefore, a 50/50 mixture of TYPE I fluids and water is normally used. Type II or Type IV fluids contain a least 50% by volume of either: S Monoethylene--glycol S Diethylene--glycol S Monopropylene--glycol S or a mixture of the above. The other 50% comprises: S inhibitors to restrict corrosion and increase the flash--point, water and wetting agents to allow the fluid to form a uniform film over the aircraft surfaces S thickening agents to enable the fluid to adhere to the aircraft surfaces for longer periods.
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De-/Anti-icing Recommendations Aircraft performance certification is based upon that aircraft having an uncontaminated or clean structure. Ice, snow and frost (or combinations of them) will disturb the airflow, affecting lift and drag. They also increase the aircraft weight. The aircraft, and especially its surfaces that provide lift and stability, must be aerodynamically clean. If they are not, safe operation is not possible. If the fuel temperature is below freezing point and the aircraft is subject to precipitation, clear ice may form on the wings (wing tank area), even if the outside temperature is as high as 15oC (59oF). An aircraft that is ready for flight must not have ice, snow, slush or frost adhering to its critical flight surfaces (wings, vertical and horizontal stabilizers and rudder).
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Figure 304
Anti Icing 3
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IR PART 66
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TWO EXAMPLES OF ANTI--ICING CODES ARE GIVEN IN THE FIGURE OPPOSITE.
THE TIME REFERRED TO IN THE ANTI--ICING CODES MUST BE THE STARTING TIME OF THE ANTI--ICING PROCEDURE.
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The Anti--Icing Code It is important that the flight crew get clear and precise information from persons who have carried out any de--/anti--icing procedures. In order to improve the quality of communication between the de--/anti--icing team and the flight crew, it is recommended that an anti--icing code be used. This will enable the flight crew to assess the Holdover Time. This code must contain the following information : S Type of fluid S Percentage of fluid to water (for Type II and Type IV fluids only) S Time de--/anti--icing application began (preferably local time).
M7.17 (Cat A)
IR PART 66
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Time of Protection The time of protection will be shorter in very bad weather conditions. High wind speeds and jet blast can cause damage to the protective film. If these conditions occur, the time of protection will be much shorter. The time of protection can also be much shorter if the wing temperature is lower than the OAT. Because conditions are not always the same, a pre--take--off inspection is necessary when you use the times given in the tables. These procedures prevent the formation of ice in some zones (wings, vertical and horizontal stabilizers, rudder) and make easier for the removal of snow from the the aircraft.
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Holdover Times Holdover times are the estimated times that the applied anti--icing fluid will prevent the formation of frost, ice and the accumulation of snow on the protected surfaces of an aircraft. When applying first-step de/anti--icing process, the holdover time is from the start of the de/anti--icing application. When applying second-step de/anti--icing process, the holdover time is from the start of the anti--icing application. The holdover times given are for general information only. The indicated time of protection may be shortened : S In severe weather S In high winds and jet blasts S By the age and condition of the fluid S By the method of application.
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Figure 305
ISO Type I / 16.43 UTC
Anti-Icing Codes
Type of fluid used
Universal coordinated time of start application
Type of fluid used
% of fluid/water by vol: 75% fluid / 25% water
Local time of start of the application
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AEA Type II / 75/ 16.43 local
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Pneumatic Ground Supplies On some aircraft this would be taken as the supply of compressed gas for the charging of gas bottles, oleos etc. On other aircraft the term ”pneumatics” would mean the supply air for cabin air conditioning/ pressurisation -- usually for the jet engine to the air conditioning packs. When dealing with compressed gas from pressurised transportation gas bottles always check the following: Check transportation bottles are within test date. Ensure that the correct gas is used -- air -- nitrogen etc (check AMM). Ensure system is serviceable to charge. Charge slowly. When using an adapter gauge always ensure that the pressure readings from the various gauges -- charging bottles, adapter, aircraft -- all read the correct reading. Stop the charging if readings do no correlate, and investigate the reasons why. Ensure that adapter gauge is within test date. Allow pressure to stabilise after charging. Check any pressure/temperature graphs. Fit all blanks. Supplies for cabin pressurisation air usually come from an engine driven ground supply trolley/ cart. The duct connection must be clean and the system must be checked that it is not pressurised before connection is made. The system must also be checked that it is serviceable before air supply commences.
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Electrical Ground Supplies For dc supplies a set of batteries mounted on a trolley or an engine driven dc generator may be used. The master switch on the trolley is off before connection is made. The aircraft services switches are either off or their position corresponds with the service selection -- ie flaps up, selector switch up. The AMM is consulted before power is applied. The power supply plug (and the aircraft socket) may vary in design. The plug consists of three pins, handed so it cannot be fitted to the aircraft the wrong way round. The centre large pin is the main supply pin, the other large pin is an earth/ground pin. The small pin is a relay control pin. When plugged in and the master switch on, it supplies a small current to operate a relay on the aircraft which switches out the aircraft battery supply and switches in the external supply (centre pin) to the dc bus bars. It also causes a cockpit indicator to show that external power is on. When the external master switch is switched off the relay resets, external power is switched off and internal power (batteries) are switched onto the busbars. For ac supplies an engine driven ground cart is used. The power supply socket usually contains 6 pins, handed, so fitment to the aircraft can only be made in the correct orientation. Three large pins are for the supply of the 3 phases, with the forth large pin being a ground/earth connection. The two small pins are dc control pins which operate relays on the aircraft to switch in/out the external power supply. There are two power supply connections -- the primary and the secondary. The
The air supply cart should have a certificate of serviceability both in relation to it’s motive power, exhaust emission, and quality and rate of air supply. When operating the unit ensure: A fire extinguisher is available. It is placed as far away from the aircraft as possible consistent with the ability to connect the supply hose. Its air supply rate is within the parameters laid down in the AMM (pressure and supply rate). When disconnecting ensure that the pressure is released. The aircraft is configured to accept the supply and the pneumatic system is serviceable.
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Introduction From time to time, most large aircraft require some form of auxiliary power to start the engines, provide electricity while the aircraft is on the ground, or provide cabin heating or cooling. For this reason, various types of ground power units (GPUs) are available for supplying power when the engines are not running. Some GPUs are mobile units that are driven to the aircraft while others are pulled behind a tug. Some newer airports have power and air outlets built into the tarmac.
GROUND SERVICING EQUIPMENT
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primary is to be used first with the secondary being connected if more power is required. On many aircraft there is only one external power connection.The panel shows the connection status of the supplies together with support strapping for the (heavy) power supply cable. In general, power supply panels have the following equipment/ indications: S 3 external ac power circuit breakers. S dc control circuit breakers. S Power connected/power ON lights. S Panel illumination lights. S Interphone socket. S Pilot’s call button. S To connect power: S Check the AMM. S Ensure all switches are off or set to the position of the service to which they relate. S Check that supply cart engine is running correctly and voltage and frequencies are correct. The same precautions apply here as for any internal combustion engine powered equipment running in the vicinity of aircraft. S Insert ground power plug and support using restraining straps. S Turn power on at the supply. S Check ”power available” lights come on, on the aircraft panel. If they do not then supply voltage or frequency may be a problem. S If ”power available” lights are on, press ground service power switch on panel to apply power to the aircraft ground service busbar. Note indications. S Press the primary power switch to apply power to the aircraft power supply bus bars. Note indications.
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AC Supply Socket
DC and 3 Phase Connectors
Connect together
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Electrical Servicing/Starting Trolley Figure 306 May 2004
’Power On’ Indicators
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Obstruction Warning Lamps
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Operate clutch to engage pump -- note that no services move. If they do, either dis--engage the pump or check whether they are supposed to move and are prepared for it (AMM). Check pressure gauges, low pressure warning lamps etc in the flight deck. After all testing is completed and the landing gear is locked down with ”3 greens” the clutch can be dis--engaged and the rig shut down. Using a ”C” spanner or special tool undo the self--seal couplings. No fluid should leak, but if it does then ensure the self seal coupling seals correctly and the leak stops, fit the blank and check the level of the reservoir.
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Hydraulic Ground Supplies The term hydraulic ground supplies could include refill connections, system selector valves etc, but these paragraphs will concentrate on the supply of external hydraulic power. The hydraulic system may require the use of more that one external power test rig/cart -- check the AMM. The test rig/ cart is usually powered by an internal combustion engine and should meet the safety requirements applicable to all these type of engines when operating in the vicinity of aircraft. The test rig must be fitted with the same type of pump that is fitted to the aircraft -- or as specified in the AMM. The rig must be run at the rpm as specified on the rig instruction panel to meet the pressure and volume flow rate requirements as required by the aircraft. The test rig should be checked to see if it contains the correct hydraulic fluid -normally marked on a plate fixed to the rig -- if it doesn’t, get a rig that does. It is connected to the aircraft using hoses with self--seal quick release connections. They are sized so that the hoses cannot be cross--connected: For 2 hose connections. Large = suction line. Small = pressure line. For 3 hose connections. Large = suction line. Medium = pressure line Small = idling line. Check the following when connecting/ disconnecting hydraulic power: Check the AMM. Carry out the normal safety precautions in relation to the running of an internal combustion engine in the vicinity of aircraft. Check that the hydraulic system and all associated systems are serviceable and ready to be tested (fluid levels, accumulator gas pressures, completeness etc). If the landing gear is to be tested the aircraft should be on jacks and suitably trestled/ shored. Check flight deck selectors correspond with actual position of systems. Have electrical power on. Connect hydraulic hoses. Start hydraulic test rig -- adjust to correct rpm -- allow to warm--up.
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M7.18A TYPES OF DEFECT AND VISUAL INSPECTION TECHNIQUES/ CORROSION REMOVAL ASSESMENT AND REPROTECTION
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IF A COMPONENT IS SUSPECTED OF SUFFERING FROM INTERGRANNULAR CORROSION, THEN IT MUST BE REPLACED.
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Metal Fatigue Metal fatigue can be briefly described as a weakening of a metal part under repeated applications of a cycle of stress. The weakening effect can be seriously accelerated by corrosion of the metal. In the early stages, fatigue damage is difficult to detect by visual inspection and the method of non--destructive examination is usually specified (the method used depending on the type of structure and material concerned).
NOTE:
Corrosion Corrosion comprises many types such as crevice, intergrannular and filliform. Corrosion can generally be said to be the process whereby a material, through Electro-Chemical action, oxidises to form salts or powders. The presence of corrosion in aircraft structures is liable to result in conditions which may lead to catastrophic failures. It is therefore essential that any corrosive attack is detected and rectified in the earliest stages of its development. By the nature of their operation, aircraft are exposed to frequent changes of atmospheric temperature and pressure and to varying conditions of relative humidity; therefore, all parts of the structure are subject to some form of condensation. The resultant water takes into solution a number of corrosive agents from the atmosphere or from spillages (which convert the water into a weak acid) and will corrode most metal surfaces where the protective treatment has been damaged or is inadequate. Cases of serious corrosion have been found in both closed and exposed parts of structures of aircraft operated under a wide variety of conditions.
Introduction This section gives general guidance on the inspection of those parts of a metal aircraft structure which, because of their remoteness, complexity or boxed--in design, are not readily accessible for routine maintenance or require special attention in the light of operational experience. Deterioration may arise from various causes and can affect various parts of the structure according to the design of the aircraft and the uses to which it is put. Essentially, the main types of defects being inspected for are corrosion and metal fatigue.
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Cleanliness It is important that aircraft should be thoroughly cleaned periodically. Care should be taken not to damage protective treatments when using scrubbing brushes or scrapers. Any cleaning fluids used should have been approved by the aircraft constructor. For final cleaning of a boxed--in type of structure an efficient vacuum cleaner, provided with rubber--protected adaptors to prevent damage, should be used. The use of air jets should be avoided as this may lead to dirt, the products of corrosion, or loose articles, being blown from one part of the structure to another.
In the majority of cases the presence of fatigue damage is revealed by the formation of a small hairline crack or cracks. Those parts of a structure where fatigue damage may occur are determined by design calculations and tests based on the expected operational use of the aircraft and substantiated by operational experience. At the periods specified in the appropriate publications, examination or renewal of the parts will be required. These periods are usually in terms of flying time or the number of landings, or from readings logged by load recording instruments. With certain materials and structures, renewal or sampling checks may be required on a calendar basis. It is important to note that some parts of a structure may be liable to fatigue damage resulting from unforeseen causes, e.g. parts damaged or strained on assembly, invisible damage to the structure during assembly or maintenance work, or fretting. When carrying out inspections it is important to check carefully for any signs of cracks emanating from points of stress concentration such as bolt--holes, rivets, sharp changes in section, notches, dents, sharp comers, etc. Fatigue damage can also be caused by pits and notches created by corrosion, although the corrosion may no longer be active. During the application of repeated stress cycles, crevices can be opened up and may eventually result in a fatigue failure. NOTE: Poor fitting or malassembly can reduce fatigue life considerably. A spar has been known to fail under tests at a fraction of its normal life as a result of the stress concentration caused by a tool mark in a bolt--hole. Defects such as a burr on a bolt can cause a scratch inside the bolt--hole, which can seriously accelerate fatigue damage in a stressed member.
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INSPECTION OF METAL AIRCRAFT STRUCTURES
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Crack emanating from lightning strike
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Figure 307
Crevice corrosion
Defect Examples
Exfoliation or layer corrosion
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Stress cracking
Intergranular corrosion
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General The structure should be examined for any signs of distortion or movement between its different parts at their attachment points, for loose or sheared fasteners (which may sometimes remain in position) and for signs of rubbing or wear in the vicinity of moving parts, flexible pipes, etc. NOTES 1. A wing structure has been known to have had a rib sheared at its spar attachments due to the accidental application of an excessive load, without any external evidence of damage, because the skin returned to its original contour after removal of the load. 2. (For the inspection of bolted joints) The protective treatment should be examined for condition. On light alloys a check should be made for any traces of corrosion, marked discolouration or a scaly, blistered or cracked appearance. If any of these conditions is apparent the protective treatment in the area concerned should be carefully removed and the bare metal examined for any traces of corrosion or cracks. If the metal is found satisfactory, the protective treatment should be restored. NOTE: To assist in the protection of structures against corrosion some constructors may attach calcium chromate and/or strontium chromate sachets to the vulnerable parts of the structure. The presence of chromate in the sachets can be checked by feel during inspection. After handling these materials, the special precautions, e.g. hand washing, given in the constructor’s manual, should be followed. 3. In most cases where corrosion is detected in its early stages, corrective treatment will permit the continued use of the part concerned. However, where the strength of the part may have been reduced beyond the design value, repair or replacement may be necessary. Where doubt exists regard-
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Visual Examination Nearly all the inspection operations on aircraft structures are carried out visually and, because of the complexity of many structures, special visual aids are necessary to enable such inspections to be made. Visual aids vary from the familiar torch and mirrors to complex instruments based on optical principles and, provided the correct instrument is used, it is possible to examine almost any part of the structure. NOTE: Airworthiness Requirements normally prescribe that adequate means shall be provided to permit the examination and maintenance of such parts of the aeroplane as require periodic inspection. In order that the necessary repair procedures can be determined, the type and extent of damage must be properly and thoroughly investigated. To determine the damage category, the suspected or affected area must be prepared by removing any foreign matter deposits from the component surface, cutting out any broken, bent, heated, burnt or otherwise obviously damaged areas of the component and removing loose rivets where apparent. S In addition to the damaged or affected area itself, any adjacent attachment points and/ or connections, through which abnormal loads may have been transmitted, must be fully investigated. S If misalignment or twisting of the airplane structure is suspected, alignment and/ or levelling checks must be carried out.
ing the permissible extent of corrosion, the manufacturer should be consulted. 4. The edges of faying surfaces should receive special attention; careful probing of the joint edge with a pointed instrument may reveal the products of corrosion which are concealed by paint. In some instances slight undulations or bumps between the rivets or spot welds, or quilting in areas of double skins due to pressure from the products of corrosion, will indicate an advanced state of deterioration. In some cases this condition can be seen by an examination of the external surface, but dismantling of parts of the structure to verify the condition of the joints may be required. NOTE: To avoid damage to the structure, the probing of a joint with a pointed instrument should be carried out with discretion by an experienced person. Any damage done to the protective paint coating, however small, should be made good.
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Inspection Techniques The structure should be maintained in a clean condition and a careful check should be made for any signs of dust, dirt or any extraneous matter, especially in the more remote or ’blind’ parts of the structure. Loose articles such as rivets, metal particles, etc., trapped during construction or repair, may be found after the aircraft has been in operation for some considerable time. It is important to examine these loose articles to ensure that they did not result from damaged structure. It is generally easy to determine if a loose article has formed part of the structure by its condition, e.g. an unformed rivet could be considered as a loose article, but a rivet which had been formed would be indicative of a failure.
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Figure 308
Visual Examination
Mk 1 Eyeball
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Endoscopes An endoscope (also known as an introscope, boroscope or fibrescope, depending on the type and the manufacturer) is an optical instrument used for the inspection of the interior of structure or components. Turbine engines, in particular, are often designed with plugs at suitable locations in the casings, which can be removed to permit insertion of an endoscope and examination of the interior parts of the engine. In addition, some endoscopes are so designed that photographs can be taken of the area under inspection, by attaching a camera to the eyepiece; this is useful for comparison and record purposes. One type of endoscope comprises an optical system in the form of lenses and prisms, fitted in a rigid metal tube. At one end of the tube is an eyepiece, usually with a focal adjustment, and at the other end is the objective head containing a lamp and a prism. Depending on the design and purpose of the instrument a variety of objective heads can be used to permit viewing in different directions. The electrical supply for the lamp is connected near the eyepiece and is normally supplied from a battery or mains transformer. These instruments are available in a variety of diameters from approximately 6mm and are often made in sections which can be joined to make any length required. Right--angled instruments based on the periscope principle are also available for use where the observer cannot be in direct line with the part to be examined. A second type of endoscope uses ’cold light’; that is, light provided by a remote light source box and transmitted through a flexible fibre light guide cable to the eyepiece and thence through a fibre bundle surrounding the optical system to the objective head. This type provides bright illumination to the inspection area, without the danger of heat or electrical sparking and is particularly useful in sensitive or hazardous areas. A third type of endoscope uses a flexible fibre optical system, thus enabling inspection of areas which are not in line with the access point.
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Focusing ring
Eyepiece lens
Light guide Protective sheath
Control handles for 4--way tip articulation
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Typical Endoscope Application
Flame Tube
Igniter plug hole
Fibre optic cable from light box
Focus control
Light guide exit
Burner
Endoscope
Projection lamp
Objective lens
Interchangeable tips
Figure 309
Image guide
Operating handle
Eyepiece
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Combustion chamber
Nozzle guide vanes
By-Pass Duct
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Magnifying Glass The magnifying glass is a most useful instrument for removing uncertainty regarding a suspected defect revealed by eye, for example, where there is doubt regarding the presence of a crack or corrosion. Instruments vary in design from the small simple pocket type to the stereoscopic type with a magnification of 20x. For viewing inside structures, a hand instrument with 8x magnification and its own light source is often used. Magnification of more than 8x should not be used unless specified. A toopowerful magnification will result in concentrated viewing of a particular spot and will not reveal the surrounding area. Magnification of more than 8x may be used, however, to re--examine a suspected defect which has been revealed by a lower magnification.
Inspection Mirrors Probably the most familiar aid to the inspection of aircraft structures is a small mirror mounted at one end of a rod or stem, the other end forming a handle. Such a mirror should be mounted by means of a universal joint so that it can be positioned at various angles, thus enabling a full view to be obtained behind flanges, brackets, etc. A useful refinement of this type of mirror is where the angle can be adjusted by remote means, e.g. control of the mirror angle by a rack and pinion mechanism inside the stem, with the operating knob by the side of the handle, thus permitting a range of angles to be obtained after insertion of the instrument into the structure. Mirrors are also made with their own source of light mounted in a shroud on the stem and are designed so as to avoid dazzle. These instruments are often of the magnifying type, the magnification most commonly used being 2x.
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When using any form of magnifier it is most important to ensure that the surface to be examined is sufficiently illuminated.
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Light Probes It is obvious that good lighting is essential for all visual examinations and special light probes are often used. For small boxed--in structures or the interior of hollow parts such as the bores of tubes, special light probes (fitted with miniature lamps) are needed. Current is supplied to the lamp through the stem of the probe from a battery housed in the handle of the probe. These small probes are made in a large variety of dimensions, from 5mm diameter with stem lengths from 50mm upwards. Probes are often fitted with a magnifying lens and attachments for fitting an angled mirror. Such accessories as a recovery hook and a recovery magnet may also form part of the equipment.
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Lamp
Typical Light Probe
Light probe
Sleeve with elliptical mirror
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Figure 310
Battery handle
Magnifying lens
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ALLOWABLE DOES NOT MEAN THAT REPAIR IS UNNECESSARY. FOR EXAMPLE, SCRATCHES AND BURRING ARE INCLUDED IN THIS CATEGORY, AND IT IS NECESSARY TO REMOVE ROUGH AND SHARP EDGES AND SMOOTH OUT THE DAMAGE. ADDITIONALLY, ANY DAMAGE TO SURFACE COATINGS AND/ OR PROTECTIVE TREATMENT MUST BE REPAIRED USING AM
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Allowable Damage Allowable damage is defined as damage which is slight or of little significance, and is unlikely to be of sufficient severity to propagate further damage in the immediate vicinity.
The damage must be classified either as ”Allowable Damage” or ”Non-Allowable Damage” (requiring a repair).
REPAIRABLE DAMAGE
Examination of damage In order to facilitate the correct repair, once damage has been found, the full extent and category of the damage must be determined. After cleaning and investigating the damage and surrounding area, it can be classified into one of the following categories (taking into account the location of the damage). It is also important to consider what secondary damage may have occured to the structure when carrying out an inspection of the damaged area. This is particularly important when the damage has been caused by shock to the structure, and the load path from the point of impact may be some distance away from the observed damage.
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Non-repairable Damage Non-repairable damage is defined as damage to structural components which cannot be repaired and where replacement of the complete component is recommended as a repair is not practical or economical.
Non-Allowable Damage Damage which exceeds the ”Allowable Damage” limits must be repaired by removing the damaged area of a structural component and inserting or attaching a reinforcing piece. These specific repairs are to be found in each chapter of the SRM.
APPROVED PROCEDURE DEALT WITH UNDER SRM CHAPTER 51.
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General The term damage refers to any permanent deformation or alteration of the cross section of a structural component. Their are four general groups of action that may cause damage, they are: S Mechanical action S Chemical action S Thermal action S Inherent metallic properties
DAMAGE CLASSIFICATION
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Distortion S Any twisting, bending or permanent strain which results in misalignment or change of shape. May be caused by impact from a foreign object, but usually results from vibration or movement of adjacent attached components. This group includes bending, buckling, deformation, imbalance, misalignment, pinching and twisting.
Dent S A dent is normally a damage area which is depressed with respect to its normal contour. There is no cross sectional area change in the material; area boundaries are smooth.
Crack S A crack is a partial fracture or complete break in the material with the most significant cross-sectional area change.
Gouge S A gouge is a damage area of any size which results in a cross--sectional area change. It is usually caused by contact with a relatively sharp object which produces a continuous, sharp or smooth channel-like groove in the material.
Scratch S A scratch is a line of damage of any depth and length in the material and results in a cross-sectional area change. It is usually caused by contact with a very sharp object.
Mark S A mark is to be understood as a damage area of any size where an accumulation of scratches, nicks, chips, burrs or gouges etc is present in such a way that the damage must be treated as an area and not as a series of individual scratches, gouges etc.
General In order to facilitate the classification of different repair procedures, the various types of damage are grouped as follows:
TYPES OF STRUCTURAL DAMAGE
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Dent
Scratch
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Figure 311
Types of Structural Damage 1
Distortion
Gouge
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Crease
Crack
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Burn Marks (Lightning Strikes) S Burn marks/ lightning strikes are usually spot formed welded damages with discoloration of the material.
Hole S A hole constitutes a complete penetration of the surface. It is usually caused by impact of a sharp object.
Delamination/ Debonding S Delamination or debonding is the separation of a laminate into its constituent layers.
Crazing S A mesh of minute hairline surface cracks.
Nick S A small loss of material, due to a knock etc at the edge of a member or skin.
Abrasion S An abrasion is a damage area of any size which results in a cross-sectional area change due to scuffing, rubbing, scraping or other surface erosion; it is usually rough and irregular.
Crease S A damage area which is depressed or folded back upon itself in such a manner that its boundaries are sharp or well defined lines or ridges.
Corrosion S The destruction of metal by chemical or electrochemical action.
TYPES OF STRUCTURAL DAMAGE (CONTINUED)
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Debonding (Stringer)
Delamination
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Figure 312
Types of Structural Damage 2
Hole
Abrasion
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Burn Marks
Nick
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Visual Inspection The following list details some of the equipment to help do a visual inspection for corrosion: S magnifying glass, S mirrors, S borescope, fiber optics, S other equivalent equipment.
Inspection Corrosion can be found by the following methods: S visual inspection, S dye penetrant inspection, S ultrasonic inspection, S eddy current inspection, S X--ray inspection. The applicable procedures are given in the Nondestructive Testing Manual (NTM).
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Appearance When inspecting a painted surface, corrosion is usally seen as: S a scaly or blistered surface, S a change of colour, S blisters in the paint. When there is corrosion on a metallic surface you will usually see a dulled or darkened area and a pitted surface. White, grey or red dust or particles may also be observed.
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Introduction The early identification and removal of corrosion will help to maintain the serviceability, safety and function of the aircraft. This is only possible if the inspection for corrosion is done regularly and precisely. All corrosion found must be immediately and completely removed. This is essential because corrosion which remains will cause new corrosion and further decrease the strength of the structure. After the corrosion is completely removed the extent of the damage must be examined and compared with the allowable damage limits (Chapter 51--11--00 of the AMM). Ensure that the repair area is given the correct surface protection to prevent further corrosion (Chapter 51--21--00).
CORROSION REMOVAL
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Preparation 1. Before starting to remove corrosion, protect all adjacent areas/equipment against the effect of chemical strippers, cleaning agents and surface treatment materials. Use suitable masking paper and tape. WARNING: CLEANING AGENTS ARE DANGEROUS. 2. Remove all dirt, grease and other foreign matter from the affected area with cleaning agent. NOTE: Do not use cleaning agent (Material No. 11--004) on titanium parts located within high temperature areas (above 150oC (300oF)). 3. Two methods of paint removal are possible; mechanical and chemical. 4. Where the corrosion is light and contained within a small area, use the mechanical method. Where the corrosion is heavy and covers a large area, the use of paint strippers is recommended. 5. Any fasteners located within the area of corrosion and affected by the corrosion must be removed to prevent cross contamination between dissimilar metals whilst the corrosion is being removed. Removal of the fasteners will also permit a check for corrosion in the bore of the fastener holes.
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1. All areas of structural items or parts that are affected by corrosion are to be treated immediately. NOTE: It is advisable to make an initial assessment of the extent of the corrosion. It may be less costly (Man--hours and/or materials), to make a repair than proceeding with the steps that follow. 2. In order to determine the extent of the damaged area, all corrosion must first be removed. Removal of corrosion should be done by trained personel. Refer to the applicable Chapter 52 - 57 to determine the type of repair if required. 3. Ensure that all corrosion is completeiy removed before starting a repair. Minor residues of corrosion can act as a starting point for further corrosion. 4. The following are a series of steps as a guide to corrosion removal. Depending on the situation not all steps will be applicable: S clean the corroded area, S remove paint from the corroded area, S further cleaning of the area, S removal of corrosion, Check for complete removal of corrosion. If corrosion is still present, proceed with the above work step removal of corrosion, S blending out of affected area, S check of allowable damage and repair if required, S final cleaning, S surface treatment. NOTE: In case of installed fasteners in the area of corrosion, it is necessary to remove all fasteners before starting with the removal procedure (refer to Chapter 51--42--00). 5. Refer to Chapter 51--22--00 for information on the various types of corrosion and methods available for preventing corrosion. 6. Peening the surface after corrosion removal. S For areas up to 10000 mm2 (15.50 in2) peening is recommended but not required. S For areas > than 10000 mm2 (15.50 in2) but < than 19000 mm2 (29.45 in2), flap peen (Refer to Chapter 51--29--11) or shot peen with steel balls. S For areas > 19000 mm2 (29.45 in2) shot peen with steel balls.
CORROSION REMOVAL (CONT’D)
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Commercial mushroom sanding pad with aluminium oxide abrasive discs of various grades. Diameters approx 25mm, 50mm or 75mm.
Commercial Spirapoint cones with adaptor cone.
Corrosion Removal Tools
Commercial flexible sanding wheel, aluminium oxide abrasive Grade 80.
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Figure 313
Commercial rotary files of ball and conical shape.
Commercial drum sander with aluminium oxide abrasive sleeves of various grades, lengths and diameters.
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Rotary Files The use of a rotary file or hand scraper is necessary when the corrosion is heavy. Rotary files are suitable for use on aluninium and steel alloys. 1. Do the necessary preparation steps (previous page). WARNING: THE USE OF SAFETY GOGGLES OR A FACE SHIELD IS MANDATORY WHEN USING MOTOR-DRIVEN ROTARY FILES. 2. Remove corrosion as necessary using a rotary file. 3. Using fine abrasive paper, polish the surface to a standard suitable for final treatment. Abrasive Blasting NOTE: Abrasive blasting is not recommended for use internally. Abrasive blasting is a widely used method of cleaning or finishing metal surfaces. In this procedure the metal surface is bombarded with a stream of abrasive particles. It is also a quick method of removing filiform corrosion and scale from metal surfaces. Suitable portable abrasive blasters are available. 1. Do the necessary preparation steps (previous page). WARNING: THE USE OF SAFETY GOGGLES OR A FACE SHIELD IS MANDATORY WHEN USING ABRASIVE BLASTING. WARNING: AVOID INHALATION OF ABRASIVE DUST. GOOD VENTILATION IS NECESSARY. 2. Remove the corrosion by blasting with glass beads. NOTE: To obtain the best results, the gun nozzle should be positioned so that the glass beads remove the corrosion in a path approximately 25mm wide.
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Corrosion Removal Techniques Abrasion by Hand Abrasion by hand is only suitable for areas of light corrosion. Emery cloth and abrasive pads are the most common methods used. Wire Brushing S Wire brushing is a mechanical abrasive operation that can be done with either a hand brush or motor driven brush. S Wire brushing, as described below, is a typical procedure used to remove heavy corrosion and embedded paint or dirt. 1. Do the necessary preparation steps (previous page). 2. Remove any loose corrosion with a hand scraper. WARNING: THE USE OF SAFETY GOGGLES OR A FACE -SHIELD IS MANDATORY WHEN USING MOTOR-DRIVEN WIRE BRUSHES. CAUTION: ONLY USE STAINLESS STEEL OR ALUMINUM OXIDE-COATED BRUSHES. 3. Using a wire brush , remove all traces of corrosion. Grinding S Grinding is a procedure used to remove corrosion using motorised grinding wheels. 1. Do the necessary preparation steps (previous page). WARNING: THE USE OF SAFETY GOGGLES OR A FACE SHIELD IS MANDATORY WHEN USING MOTOR-DRIVEN GRINDING WHEELS. CAUTION: AVOID GENERATING HIGH TEMPERATURES WHEN GRINDING. THIS MAY CHANGE THE MECHANICAL PROPERTIES OF THE MATERIAL. CAUTION: GRINDING IS NOT SUITABLE FOR USE ON ALUMINUM ALLOYS. 2. Remove corrosion by grinding until a firm corrosion free surface is achieved. Continue grinding to remove any coarse irregularities. 3. Using fine abrasive paper, polish the surface to the desired finish.
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Figure 314
Abrasive Bead-Blasting
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Neutralization CAUTION: THIS PROCEDURE IS NOT SUITABLE FOR USE WHERE THE NEUTRALIZING AGENT CAN GET INTO AREAS WHERE IT CANNOT BE WASHED OFF. CAUTION: ONLY USE NEUTRALIZING AGENT WHEN WASH PRIMER IS TO FOLLOW. Neutralization can be used to complete the corrosion removal where deep corrosion was found on aluminium alloys. The following is a typical neutralizing procedure. WARNING: NEUTRALIZING ACID Cr03 IS DANGEROUS. 1. Prepare a solution, 90g of Cr03 to 1 litre (O.198 lb to 0.2642 US gaL) of water. Apply the solution to the area with a brush. 2. Allow the neutralizing agent to work for approximately 5 to 20 minutes. 3. Rinse off the neutralizing agent with running water, remove any brown or yellow discolouration with a brush. 4. Dry the area with clean, lint-free cloths.
Checks for Corrosion Removal Ensure that the corrosion has been completely removed. A x10 magnifying glass is recommended for this check. When a check for cracks is required, refer to the Non Destructive Testing Manual (NTM) Chapter 51--10--02, Page Block 101, and Chapter 51--60--00, Page Block 601. Blending of the area after corrosion removal is recommended in order to obtain a smooth surface for the application of the final surface treatment. Blending can be done with emery cloth or an abrasive pad.
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Corrosion Removal 1. Do the necessary preparation steps (previous pages). CAUTION: DO NOT USE CARBON STEEL BRUSHES OR STEEL WOOL ON ALUMINIUM ALLOY SURFACES. TINY DISSIMILAR METAL PARTICLES WILL BECOME EMBEDDED IN THE ALUMINIUM ALLOY AND CAUSE FURTHER CORROSION WITH RESULTING DAMAGE TO THE PART. 2. Remove light corrosion with the use of emery cloth (Grade 240 to 400). CAUTION: AVOID GENERATING HIGH TEMPERATURES WHEN USING SCRAPERS, ROTARY FILES OR STAINLESS STEEL BRUSHES. THIS MAY CHANGE THE MECHANICAL PROPERTIES OF THE MATERIAL. 3. Remove heavy corrosion using scrapers, rotary files or stainless steel brushes. 4. Do the ’Checks for Corrosion Removal’ and ’Neutralization’ work steps as applicable. WARNING: CLEANING AGENTS ARE DANGEROUS. 5. Clean the area with cleaning agent. 6. Refer to the NTM, Chapter 51--10--04, Page Block 101, and establish the remaining material thickness. 7. Refer to Chapters 52 - 57 (Page Block 101) as applicable, and establish if further action is necessary. 8. Apply the appropriate surface protection as given in Chapter 51--75--12. 9. If applicable, renew any special coatings in the area (refer to Chapter 51--23--12).
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Corrosion Removal 1. Do the necessary preparation steps (previous pages). CAUTION: HAND-HELD POWER TOOLS MUST NOT BE USED ON HIGH STRENGTH STEEL. TO AVOID OVERHEATING, EXERCISE EXTREME CARE WHEN REMOVING CORROSION WITH TOOLS. 2. Remove the corrosion using abrasion by hand, stainless steel brushes or abrasive blasting. 3. Clean the area with cleaning agent. 4. Do the ’Checks for Corrosion Removal’ and ’Neutralization’ work steps as applicable. 5. Refer to the NTM, Chapter 51--10--04, Page Block 101, and establish the remaining material thickness. 6. Refer to Chapters 52 - 57 (Page Block 101) as applicable and establish if further action is necessary. 7. Apply the appropriate surface protection as given in Chapter 51--75--12. 8. If applicable, renew any special coatings in the area (Chapter 51--23--12).
Carbon steel in its heat-treated form is used in those areas where high structural or aerodynamic loads occur on the aircraft. Red iron rust is one of the more familiar types of corrosion found on carbon steel. This type of corrosion is generally caused by the formation of ferrous oxides due to atmospheric exposure. Red iron rust attracts moisture from the atmosphere which promotes additional corrosion. Red rust first shows on unprotected aircraft hardware such as bolts, nuts and exposed fittings. Slight corrosion on highly stressed steel parts is potentially dangerous and the rust must be removed and controlled. Corroded steel parts should be removed from the aircraft where possible, for treatment.
Aluminum alloys are the most widely-used materials in the construction of aircraft. The most obvious sign of corrosion is a whitish deposit on the surface of the metal, caused by chemical action. General etching, pitting or roughness of the surface gives an indication of the early stages of corrosion. Procedures for the removal of corrosion are as follows.
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REMOVAL OF CORROSION FROM CARBON STEEL
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CORROSION ON ALUMINIUM ALLOYS
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Titanium alloys are used in various areas in the aircraft structure, especially in high temperature areas and areas where high strength members are exposed to a corrosive environment. Exposure of the surface of titanium to fire resistant hydraulic fluids (Skydrol) causes hydrogen embrittlement with subsequent pitting of the surface. Titanium alloy is generally resistant to corrosion. Corrosion however, when it does occur is recognized as a black or white coloured oxide. Corrosion Removal WARNING: SMALL CHIPS OR SLIVERS OF TITANIUM THAT RESULT FROM MACHINING CAN EASILY IGNITE, AND ARE TO BE CONSIDERED AS AN EXTREME FIRE HAZARD. IN THE CASE OF A FIRE DEVELOPING, EXTINGUISH WITH DRY TALCUM POWDER, CALCIUM CARBONATE, SAND OR GRAPHITE. DO NOT USE WATER, CARBON DIOXIDE, CARBON TETRACHLORIDE OR ORDINARY DRY CHEMICAL FIRE EXTINGUISHERS. 1. Do the necessary preparation steps (previous pages). 2. Remove the corrosion or surface deposits by hand polishing. Use a soft clean cloth together with aluminum polish. 3. Clean the area with cleaning agent (Material No. II--003 or 11--004).
CORROSION REMOVAL FROM TITANIUM ALLOYS
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The following process is suitable for removing and repairing corrosion damage to cadmium plated parts in situ. 1. Do the necessary preparation steps (previous pages). WARNING: PARTICLES OF CADMIUM ARE DANGEROUS. WEAR CORRECT PROTECTIVE CLOTHING TO PREVENT THE INHALATION OF CADMIUM PARTICLES. 2. Remove corrosion with a dampened abrasive pad. NOTE: All contaminated cloths and abrasive pads must be collected and placed in polythene bags for disposal in accordance with local instructions. WARNING: CLEANING AGENTS (MATERIAL No. 11--003 AND 11--004) ARE DANGEROUS. 3. CLean the area with cleaning agent (Material No. 11--003 or 11--004). 4. Renew the cadmium plating using the DALIC process (refer to Chapter 51--21--11, paragraph 3. A.. Alternatively, use the phosphating procedure given in Chapter 51--21--11, paragraph 3.B.. 5. Apply the appropriate surface protection as given in Chapter 51--75--12. 6. If applicable, renew any special coatings in the area (Chapter 51--23--12).
REMOVAL OF CORROSION FROM CADMIUM-PLATED PARTS
Stainless steel and nickel chromium alloys are used where corrosion resistance is one of the major considerations in the design of structural parts and components. In most applications these steels will have no other surface protection except for matching colour schemes of the surrounding structure, dissimilar metal protection or organic coatings. Stainless steels however, are not to be considered free from the possibility of corrosion occurring. Corrosion on these steels usually appears as pitting, usually black in colour. The existence of corrosion prevents a passivated environment on the surface of the steels, and creates an active--passive corrosion cell. It is necessary therefore, that the corrosion is removed completely. Corrosion Removal Use the same procedures as those given for carbon steel (refer to previous pages).
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NOTE: Do not use cleaning agent (Material No. 11--004) on titanium parts located within high temperature areas (above 150 OC (300 OF).
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CORROSION REMOVAL FROM STAINLESS STEEL AND NICKEL CHROMIUM ALLOYS
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Pretreatments Pretreatment is the initial treatment of the metal and has the following functions: S To increase the corrosion resistant properties of the metal by chemical or electrolytical procedures, S To give a good surface for the adhesion of the subsequent paint coats. One procedure that is used to prevent corrosion is to apply a thin layer of different metal. This layer has a lower electrolytical potential than the main metal. If corrosion occurs it will remove the thin layer first. This is referred to as sacrificial corrosion prevention. The table gives you the pretreatments which are usually used to give the maximum resistance to corrosion. For details of each treatment and its use refer to Chapter 51--21--11.
The maximum possible corrosion protection is given to the aircraft before it is delivered. The good corrosion resistance of the aircraft structure is the result of the interaction of different types of corrosion protection.
TYPES OF CORROSION PROTECTION PROCEDURES
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Anodizing
Chromating
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Magnesium
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Zinc Spraying
Cadmium Plating
Silver Plating
Hard Chromium or Nickel Plating
Phosphatisation
Cadmium Plating
Wash-Primer
Chemical conversion coating
Chromic or sulphuric anodizing
Pretreatment
Titanium
CorrosionResistant Steels
Steel Alloys
Aluminium Alloys
Material
Remarks
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Immerse in a bath of chromate solution
Electrolytical treatment. Decreases galvanic effects.
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M7.18 (Cat A)
Thin layer of pure zinc. Used when in contact with aluminium alloy. Decreases galvanic effects. Sacrificial protection.
Used when in contact with aluminium alloys. Decreases galvanic effects. Sacrificial protection.
Electrolytical treatment, good resistance against fretting corrosion under hot conditions.
Electrolytical treatment to prevent contact of moisture and oxygen with the steel alloy. Highly resistant to wear, low coefficient of friction.
Chemical treatment, application of zinc or manganese phosphates (sacrificial protection)
Electrolytic application of cadmium sacrificial protection
Usually used in field repairs
Chemical treatment (same function as anodizing)
Electrolytical treatment (surface gets an oxide coating)
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Aluminium
Oxidize
Electric
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EL OX AL
Eloxadizing This process is comparable to anodizing but is done with sulphuric acid.
Anodizing
Acid
Chromic
CAA
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2/3 Diffusion into the material
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Disadvantage S Eloxation layers have ceramic properties - that means they are not elastic. Parts that are subject to bending or other distortions can crack more easily because of their eloxation layer. Anodizing is used with all integrally milled structural components of Airbus airplanes. In addition it is used on all bonded surfaces and on the outer skin of the fuselage. On the A300--600 and A310 airplanes almost all surface sheet metals (as shown in the illustration) are anodized in addition to the plated coat.
When eloxadizing the natural oxide skin is thickened by chemical means.
Al - Alloy
CAA--Layer
1/3 outside of the Al-Alloy
In this case a hard and brittle layer is created, which is very resistant to wear but cracks easily.
Anodizing
Acid
Sulphuric
SAA
Sulphuric Acid Anodizing Since about 1987 Airbus Industries have used sulphuric acid anodization.
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Anodizing Is an electrolytic process that physically alters the surface of the metal to produce a tough oxide layer on the surface. Anodizing is particularly suited to use on aluminium alloys. The process uses either chromic or sulphuric acid as the electrolyte This treatment is called “CAA“ by the manufacturers.
PREPARATORY TREATMENT OF SURFACES
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THE FOLLOWING SAFETY INSTRUCTIONS HAVE TO BE OBSERVED WHEN USING SOLUTIONS, CLEANERS, CORROSIVES, ADHESIVES, CHROMIUM TREATMENT AND PAINTS: S Do not inhale the fumes for a long time. Do not use the above-mentioned materials in small rooms without sufficient ventilation. S Avoid contact of these materials with your skin. Rubber or plastic gloves must be worn when working with solutions, cleaning agents, corrosives, etching mediums, and CCC material (Alodine and Iridite). Chemical treatment of the surface is used when anodic oxidation (eloxation) is not possible or not advisable. The protective covers that are created present a good contact area for paint and improve chemical continuity. A number of methods exist for chemical treatment. In recent years, acidic surface treatments without electrical current have been introduced for aluminium and aluminium alloys. These are procedures for chromium or phosphate plating. the corrosion protection is not quite as high as with the eloxation process, but much more economical. Chromium and phosphate plating procedures differ in the kind and strength of the created layers.
NOTE:
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When chromium plating the thickness of the layers is not more than 0.001mm. Phosphate plating layers can reach a thickness of up to 0.003mm. In the maintenance manuals, standard processes manuals and structural repair manuals you will find notes for the application of these surface protection procedures.
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Chemical Conversion Coating (CCC) Alodine 1000 is used by the airplane manufacturer for coating plated aluminium. Lufthansa has replaced Alodine 1000 by Iridite 14E or Alodine 1200, because the protection provided by Alodine 1000 is insufficient. By chemical conversion coating the surface is roughened which provides a good contact for paint coatings. Also, an aluminium-chromium-oxide cover is formed which is up to 0.001mm thick and provides for a certain corrosion protection even without paint coating. This coating is insoluble by water and organic solutions and can endure minor deformation without cracking. Cutting edges, bores and worked out scratches are chemical conversion coated with Iridite 14E or Alodine 1200. Components that are subjected to operating temperatures of more than 70oC should not be treated with CCC because the adhering property of the coating will decrease. In case of larger areas the paint is applied at Lufthansa without CCC, but the first layer of paint (washprimer) also effects a chemical surface treatment and provides, together with the following layers, a good corrosion protection.
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Boeing Boeing use a two-layer system. These layers are applied to the completely pretreated sheet metal surfaces. The first layer is applied to the chromium-treated or anodized sheet metal surface.
Airbus The following three layers comprise the paint system for the Airbus outer fuselage skin: S Wash Primer (for cohesion): a passivating cohesion primer on a Polyvinylacetate base (PVA). S Paint Primer (Intermediate Primer): a Polyurethane lacquer with corrosion inhibitors like zinc-chromate or strontium-chromate, fully cured, and S Coating Lacquer: a Polyurethane topcoat.
Technical paint finishes in airplane construction are usually multi-layer paint systems.
PAINT FINISHES IN THE AREA OF THE CABIN/FUSELAGE OUTER SKIN
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All coatings that are manually painted or sprayed on components are called paint finishes. We talk about a paint finish when the applied substance builds a layer whose thickness can be measured after drying. Another property of a paint finish is that the paint can be removed with corrosives or by any other means in case of repair. A “paint system“ is the complete build up of all layers of a paint finish. The build-up of consecutive individual layers is carried out by following precise working instructions which are established in close cooperation with the paint manufacturers and the paint shops. In the course of the production of a certain aircraft type over many years, modifications to the surface preparatory treatment, the composition of primers and coating lacquer are common. A paint system that has been specified by the respective authorities is principally applicable to all aircraft types. The layers consist of type-approved specified products.
PAINT FINISHES
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2024 or 2024 CLAD 7075 or 7075 CLAD
May 2004
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Figure 315
2024 or 2024 CLAD 7075 or 7075 CLAD
Airbus Three-Layer System
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Pretreatment: CCC (Chemical Conversion Coating)
Different Paint Systems Page: 658
Primer: Polyurethane-based or Epoxy Primer (BMS 10--11 or BMS 10--79)
Topcoat: Polyurethane lacquer or Desmophen-Desmodur (DD) (BMS 10--72)
Boeing Two-Layer System
Pretreatment: CAA (Chromic Acid Anodized) or CCC (Chemical Conversion Coating)
Wash Primer: FCR (Filiform Corrosion Resistant)
Primer: Polyurethane-based or Epoxy Primer
Topcoat: Polyurethane lacquer or Desmophen-Desmodur (DD)
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Types of Surface Protection Repairs 1. Fixing. Fixing means the cleaning and maintenance of the existing paint finish. It includes the repair of small imperfections as long as they can be carried out with a paintbrush and appear to be optically justifiable. 2. Partial or Total Renewal. This requires that the existing paint finish is solid in structure and has a satisfactory adhesion. Partial or total renewal means a paint finish that is aged or damaged is partially or totally sanded and repainted (depending on analysis test). 3. Basic Renewal. Heavily-aged paint finishes with cracks, poor cohesion, dissolved by Skydrol or visible corrosion of the metal have to be completely removed. A basic renewal includes paint removal, corrosion inhibition if required and the build up of the complete paint system.
Purpose There are two main reasons for paint finishes on airplanes and airplane parts: S a pleasant finish to the outside airplane surface, and S The protection of the cabin, the structure and parts against corrosion, erosion, mechanical damage etc. Only approved paint finishes can satisfy these requirements. The wear of paint finishes in operation varies strongly from aircraft to aircraft. It depends on the area of operation, long or short haul distances etc. Apart from the normal ageing process, mechanical and chemical stresses and maintenance occurrences affect paint deterioration. Because of this, it is not laid down how and when the overhaul and renewal of the paint finish should take place. Usually the person responsible for the analysis test will determine the extent of the repair, taking into account whether there are any special requests (such as paint removal for crack testing or colour change etc). Paint finish has to be checked for general condition; that means surface polish, brittleness, cracks, colour change, satisfactory adhesion, separation due to chemicals, etc. It has to be checked very carefully to make sure there is no corrosion below the finish. If in doubt, small test areas have to be removed. When checking paint finish, the type of future stresses and duration till the next overhaul have to be taken into consideration.
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Figure 316
Paint Build-Up
Aluminium Alloy
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Wash Primer FCR
Intermediate Primer
Polyurethane Topcoat
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IF THE MINIMUM CURE TIME IS NOT OBSERVED BEFORE THE NEXT COAT, CORROSION PROTECTION AND ADHESION WILL BE IMPAIRED. In cases of humidity higher than 75% or temperatures below 15oC, the use of FCR primer is not recommended. If its use cannot be avoided, a decrease in adhesion and corrosion protection will result and the curing time will be increased. Coating lacquer must not be applied directly to the FCR primer. It must also not be used as the only corrosion protection. It is always necessary to subsequently apply Aerodur S15/90 or CF Primer 37047. Wash Primer FCR must not be applied to steels with a breaking strength of more than 180 KSI (1240 N/mm2 ). In these cases Epoxy Primer is used. When using alternative products it is important to ensure that the primer is compatible with the component to be coated (if in doubt consult the manufacturer or refer to the current specification sheets). Not observing this can lead to loss of airworthiness.
CAUTION:
Wash-Primer FCR (Filiform Corrosion Resistant) The FCR primer consists of phosphoric acid parts (which chemically react with aluminium) and zinc-chromate pigments (which act as moisture inhibitors). The primer is not to be used as a one-layer primer but must be covered with a paint or intermediate primer layer. In the interior structure the FCR primer acts as corrosion protection for the sheet metal parts. On the outer surface the FCR primer acts primarily as adhesion contact. The FCR primer improves the adhesion of the three-layer paint system on the prepared, corrosion-protected sheet metals, which have been plated, chromeplated, or anodized with chromatic acid. The pot time is 8 hours at 20oC. Depending on the humidity and temperature the curing time is between 2 and 8 hours. The thickness of the layers should be between 0.08 and 0.012mm (equivalent to one cross-coat).
PRIMER
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2.5
h
1.5
1.75
2
2.25
Figure 317
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Time
Temperature
20
25
o
C
Influence of Humidity by Application of Primer I
15
Curing at 45 - 75 % Humidity
Curing at 30 - 35 % Humidity
Curing Time
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Cure Times S Dry so that dust will not cling after 30 minutes. S Can be sprayed over after a minimum of 4 and a maximum of 72 hours. After that it has to be sanded. Depth hardening after about 4 hours (can be shortened by heating up to 125oC). Thickness of layer of one cross-coat 0.012 up to 0.015mm (dry film).
The following products are widely used: S Aerodur S 15/90 (contains strontium (SrCrO4) with intensive green/yellow colour) S Aerodur CF 37047 (chromate free, light grey-white and dull) The intermediate primer is applied to the Wash Primer or to Alodine-treated aluminium surfaces. The paint primer used by the Airbus manufacturers contains zinc-chromate and has a similar function as the above mentioned. Pot life time after preparation is 6 hours at temperatures of 18--22oC.
INTERMEDIATE PRIMER
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Figure 318
M7 MAINTENANCE PRACTICES INSPECTION, DISASSEMBLY, REPAIR AND ASSEMBLY TECHNIQUES
TIME
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15
TEMPERATURE
20
Curing at 45 - 75 % Humidity
Curing at 30 - 35 % Humidity
25
o
C
Influence of Humidity by Application of Primer II
2
2.25
2.5
2.75
3
h
to the Time to Overcoat
Influence of Temperature and Humidity
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After chemical reaction has taken place (thermo--setting), the primer is relatively resistant to chemical attack. Resistance to hydraulic oils is not guaranteed at curing times less than 72 hours. Epoxy Primers can contain zinc-chromates but no phosphoric acid. This makes them very suitable for coating steel parts with a breaking strength of more than 180 KSI / 1240 N/mm2. Phosphoric acid would cause hydrogen embrittlement. Pot life time: 4 hours Cure time: 24 hours at 18oC Resistant to hydraulic oil (short contact) after 36 hours. Resistant to hydraulic oil for 5 hours at 80oC (before oven-drying a vapourizing time of one hour is needed). If you do not observe the minimum cure times before the application of new paint, decreased adhesion and corrosion protection can result.
EPOXY PRIMER
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Nose Landing Gear
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Figure 319
Epoxy-Primer Application
Flaptracks
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Cowlings (inside)
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Coating lacquers can be protected against general aging and decay by an additional clear varnish. The life--span of a multi-layer paint finish system can thus be increased by 25 - 50%. For aviation use, a special “Clear Coat UVR“ (Ultra violet Resistant) is available. Several manufacturers have already integrated this protection into their respective coating lacquers.
Desmodur (Hardener)
Desmophen (Base Lacquer)
DD-Coating
The coating lacquer is applied as the last layer on previously-applied wash primers and intermediate primers. The application of coating lacquer is performed on all outer cabin parts which are subject to weather conditions and to such components of the interior structure as have contact with hydraulic oils or other aggressive fluids. The coating lacquer is not part of the decorative paint finish. This is applied onto the coating lacquer, but is not a technical part of the three-layer finish system. At present, airplane manufacturers and operators use identical coating lacquers. These are Polyurethane products (PU or PUR coating lacquers). Products from the following manufacturers are currently being used: S Sikkens (C21/100 or HF-High Flexible) S Cellomer S Finsh S De Soto S ICI The Sikkens Aerodur Finish HF is identical to the widely-used DD Finish.
COATING LACQUERS
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3
4
5
Time h
M7 MAINTENANCE PRACTICES INSPECTION, DISASSEMBLY, REPAIR AND ASSEMBLY TECHNIQUES
15
Top Coat
Temperature
20
Figure 320
60 - 75 % Humidity
30 - 50 % Humidity
25
Pot Life Time for Sikkens Aerodur C 21 / 100 white/grey
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C
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Direct Current Measuring - Ohmmeter S Measuring range 1 - 20 MOhm S Resistance smaller 10 MOhm S Distance between feelers 305mm S Minimum curing time 1 - 2 hours To achieve sufficient conductivity a minimum of 75% of all countersinks in composite components must be covered with electrically-conductive paint. If pore fillers are used, the antistatic primer must be applied first. In the areas of antennae covers where the antistatic primer must not be applied, the paint finish is to be applied as if it were a normal outer skin.
These products are identical to antistatic paints and antistatic primers. Antistatic primers are electrically-conductive primers for plastic components. All plastic components of the outer skin (basically in the secondary structure) must have this priming. The exception is antennae covers. Since the antistatic primer is not exposed any more after application of the coating lacquer, it is not possible to localize it optically. This means that before application of the coating lacquer and after complete hardening has been achieved, a resistance test or conductivity test must be performed by trained personnel.
ELECTRICALLY-CONDUCTIVE PAINTS
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Figure 321
Electrostatic Coating
Black areas = antennae covers
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Water-displacing inhibitors are applied: S to stop corrosion that has already started for a certain time (until the repair can be carried out) S in areas that do not permit corrosion removal or permit corrosion removal only to a certain extent and where the build-up of correct paint finish systems is also impossible. S to make the surface in susceptible areas water-repellent in addition to the paint finish systems and other surface protection treatments, to enhance corrosion protection. Water repellents have wax-like characteristics after they have dried. Their effectiveness is based on a good wetting ability and penetrating properties. They penetrate existing corrosion products to the metal surface and build a constant film. This prevents moisture and oxygen from contact with the metal and prevent the spread of corrosion. The following products are currently available in the aviation world: S LPS 3 S Boeshield T9 H5 * S Tectyl * S Adrox S Dinitrol * carcinogenic When using these materials it is imperative to cover the following components before starting work: S Electrical plug connections S Oxygen system components S Silicon parts (door seals, bearing seals, pipe fixtures) S Piston rods of hydraulic cylinders S Control cables, pulleys, cable covers
WATER-REPELLENT FLUID AND CORROSION INHIBITORS
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WHEN USING MATERIALS SUCH AS DINITROL, IT IS ESSENTIAL TO PROTECT CABLES, WIRES, SEALS AND
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DINITROL AV 100 (Type D) is a strong, wax-like film. Applied as a thixotropic fluid, AV 100 builds up a resistant, even mechanically abrasion-proof film. Under special conditions the penetration of AV 100 into narrow capillary tubes can be improved by pretreating with AV 8. Under these circumstances an intermediate cure time of the AV 8 is required. This cure time must last at least 1 hour (refer to specification sheet). Cure time of AV 100 D about 6 hours. AV 100 can be rinsed off with tri- or per- chlorethylene or Varsol. DINITROL AV 100 D replaces AV 100 and AV 100 B.
Dinitrol AV 30 is a thixotropic, special, yellowish-brown, transparent wax that doesn’t melt or bond at temperatures below 70oC. ’Thixotropic’ means ’thickened’. The compound can only be processed with some difficulty. The product builds up an elastic film which does not crack when being deformed. The product is used in airplane overhaul for long term protection of the entire cell structure. DINITROl AV 30 replaces AV 25, AV 25B, AV 50.
Dinitrol AV 8 is a highly viscous water-displacing compound with strong surface-wetting and gap-penetrating (capillary action) characteristics. After drying, this compound builds up a dry film of about 8 thickness. DINITROL AV 8 is used as a precautionary corrosion protection in the landing gear areas, pylon areas and on fittings. Existing corrosion can be stopped or inhibited by AV 8 if it cannot be removed by maintenance immediately. AV 8 can be removed with naphtha (Varsol) or with tri- or per- chlorethylene. Alkaline degreasing agents are also applicable to a certain extent. DINITROL AV 8 replaces AV 5, AV 5--2, AV 5B, AV 5 B-2.
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PARTS OF THE OXYGEN SYSTEM FROM INGRESS OF DINITROL, WHICH ATTACK SEALS AND CAN CAUSE AN EXPLOSION WHEN IT CONTACTS OXYGEN.
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The most commonly-encountered water-displacing inhibitors are manufactured by Dinitrol.
DINITROL
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Pressurised systems/components. Pressure must be released from any system where work is to be carried out. This includes pneumatic and hydraulic systems. The manual will indicate how the pressure is to be released. The same applies to
Batteries/battery circuits. The battery should be disconnected.------Capacitive type equipment. Components that contain capacitors such as high energy ignition units fitted to jet engines should be allowed to stand without power supply for the recommended period as stated on the unit/in the manual before any work is attempted. Remember, these can store enough charge to be lethal if access is gained before the time stated.
Electrical equipment. Any electrical circuits that are to be worked onshould have their fuses taken out or the circuit breakers tripped. This should be indicated by a secure tag at the fuse or C/B position to say that the circuit is made safe and the fuse or C/B should not be refitted.
All systems/components should be made safe before work commences. This will include:
Safety
The correct equipment should be available. It may include slings; hoists; special tools; special test sets/test rigs; a standard tool kit.
The correct hangarage/workshop/bench facilities should be available.
The appropriate manuals/instruction sheets/work sheets should be available.
The person doing the job should have the appropriate skills/ training/ qualifications. And, for some tasks, the correct number of qualified people should be available.
Preparation
The following is a general approach which gives an overview to the procedures to be followed. Whether working on a system or a component the job may be split into 3 areas: * Preparation * Safety * The task in hand
To dismantle and/or reassemble a specific component/system/aircraft will require a dedicated procedure which would normally be specified in the component manual or the AMM.
DIS-- ASSEMBLY AND RE-- ASSEMBLY TECHNIQUES
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Heavy items. The movement of heavy items needs pre--planning -- the correct number of personnel, correct lifting equipment, access for equipment, etc.
Items containing liquids, which may be harmful chemicals etc. This category includes hydraulic fluids, battery electrolytes, engine oils, toilet system fluids, engine fuels, coolants etc. These fluids can be harmful if in contact with the skin, eyes or ingested by mouth. They should be drained carefully into correctly labelled containers and protective clothing warn. Disposal or re--use will depend on local regulations. If in doubt do not re--use.
components such as oleos (shock absorbers), hydraulic accumulators, gas bottles (air, nitrogen etc), wheel and tyre assemblies.
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COMPONENT DISMANTLING AND RE--ASSEMBLING In general re--assembly is the reverse of dismantling. To dismantle a component proceed as follows:
If the component is to be replaced, in general: 4. Check the ‘new’ component for serviceability, correct part number, serial number etc and check it against its documentation (JAA form 1 etc). Check the Illustrated Parts Catalogue (IPC). 5. Remove the ‘old’ component, make safe, label, and return to stores. 6. Fit the ‘new’ component and test the system iaw the AMM. 7. Check if there is any avoidable reason that caused the event -- to see if it can be prevented happening again. 8. Record all the work done and sign. Details should be in the appropriate log book, eg: S Airframe log book -- airframe parts, components, engine change, propeller change, etc. S Engine log book -- any work done on the engine, propeller change, engine change. S Propeller log book -- VPpropeller change, any work carried out on the propeller, engine change. S Any item to be removed and replaced on the aircraft for a period of time should be correctly labelled and placed on its support trolley (like an engine) or placed in a storage rack. The label should have on it the aircraft registration and date of removal. 9. Any small parts removed (nuts, bolts, washers etc) should be placed in a bag and attached to the main component. 10.Any small parts removed which are not part of a larger assembly, should be placed in a labelled bag and put on the storage rack. In some hangars there is a separate spares storage rack for each aircraft. 11. All blanks should be fitted to system connections both on the aircraft and on the component. Blanks should have warning tags attached.
For some components the aircraft may have to be jacked (some stress panels, landing gear, wheels and the retraction mechanism, for example). For system components the system must be made safe (see above).
COMPONENT REMOVAL FROM THE AIRCRAFT
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1. Carry out the preparation checks as outlined above. Observe the appropriate safety precautions -- see above. S Dismantle as follows: S For riveted up items the rivets are removed by the use of a drill the same size as the hole. The rivet head is drilled off and the shank is punched out. Blind rivets might need a modified procedure. S For welded items the only way is to use welding equipment to re--melt the weld to separate the parts. S For adhesive bonded items the only technique is to destroy the bond, which will damage the two joined parts. S For clamped together parts -- flanged pipe couplings etc -- unscrew the clamp securing nuts ti loosen the clamp -- then remove. S For items secured with taper pins, remove the taper pin securing device and tap the pin out by tapping the small end lightly with a hammer. Securing devices: nuts -- unscrew; bent over legs -- straighten with pliers; peened -remove peening carefully with a file or spot miller. S Screws, bolts into captive nuts. Remove using the correct size and type of screwdriver or correct spanner/ socket. Most have a right--hand thread which means undoing by turning anti--clockwise. Remember to remove any locking devises first -- such as locking wire, split pins, cotter pins, locking plates, tab washers etc--. S Nuts. Similar to above. S Studs. Use a stud insertion and removal tool. S Quick release fasteners. These vary in design and are released in different ways -- check the AMM/component manual. S Circlips. Use special circlip pliers. Internal circlips are removed by reducing their diameter, external circlips are removed by expanding outwards.Push fit items -- such as PCBs (Printed Circuit Boards). These are removed by gently applying hand pressure to pull the board from its case. (Remember to switch off power, wear a body bonding band and ensure all other items are disconnected). Push fit items such as bearings will need a bearing press. S Any removed fasteners that can be reused, place in a secure bag and label. If the main component is a rotating balanced component then removed items must be numbered and re--fitted back to the same location they came out of. S Parts that cannot be reused or are unserviceable should be replaced. Once all securing items are removed the first dismantled part from the component
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Assembly As stated above it is usually in the reverse order of dismantling, but in general the following applies (the item numbers are related to those above): 1. New rivets are used after the joint is cleaned and jointing compound is used (check the SRM -- Structure Repair Manual). They may have to be oversize rivets due to hole enlargement -- check that this is possible. 2. There is usually not enough material left to re--weld the joint, so additional material will be required in the form of an insertion or the fitting of a new panel or panels by welding or some other approved means. 3. New material will have to be found in the form of an insert or new panels. These may be fitted by adhesive bonding, bolting, riveting etc -- depending on the manual. 4. Clamps can be re--fitted provided they are serviceable and clamping nuts torque loaded whilst gently tapping the assembly lightly with a hammer to help the clamp ‘settle’. The clamping nuts will need locking (split pins, lock wire etc). 5. Taper pins are usually replaced. The hole might need re--reaming with a taper reamer and the next larger taper pin fitted -- check the manual. Lock into position by: opening the legs if a spilt taper pin; fitting a nut (which is usually peened afterwards); peening the small end of the taper pin. 6. Screws, nuts, bolts, captive nuts, etc are replaced if necessary.Threads are lubricated, left dry, or coated with a locking compound, then tightened as per the manual. Then torque loaded if required and locked using locking wire, split pins (cotter pins) etc. Screwdrivers, spanners, sockets etc are used. Star washers are replaced. Spring washers are replaced if they have lost their springiness and/or lost their sharp edge top or bottom. 7. As 6. 8. Similar to 6. above but fitment is maybe by the use of two nuts locked to each other on the protruding end (turning down on the top nut), or the use of a stud box, or using a stud insertion and removal tool. 9. Quick release fasteners are connected in reverse to their disconnection procedure. Replace if damaged.
can be eased away. Place all parts in order, bag and label if necessary. Protect from dust and the possibility of corrosion/deterioration. Carry out any inspection/modification/tests as necessary. Replace any items that fail any inspections/tests and any that might deteriorate in the foreseeable future such as seals, locking devices etc.
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Testing After assembly the component is always tested. This can include any one, or more, of the following depending on the component.and the manual. S Bonding, continuity, equipment. S BIT tests -- various components S Capacity test -- batteries. S Leakage tests -- hydraulic components, pneumatic components, batteries. S Functional tests to include correct displays, correct inputs and outputs, movement (range, sense, speed -- rpm, cm/min -- etc), sound, vision (speakers/CRT screens). S Balance -- for balanced rotating components etc.
Bonding, continuity, equipment. · BIT tests -- various c · Capacity test -- batteries. · Leakage tests -- hydraulic components, pneumatic components, batteries. · Functional tests to include correct displays, correct inputs and outputs, movement (range, sense, speed -- rpm cm/min -- etc), sound, vision (speakers/CRT screens). * Balance -- for balanced rotating components etc. For more information regarding nuts, locking devices, torqu~loading etc you should read the book/ s in this series on Tools and Locking Devices.
10.Wire circlips should be replaced, others can be reused provided they are undamaged and retain their springiness. 11. Push fit items are fitted in reverse order to removal. 12. esting after assembly the component is more, of the following dependingmanual. always tested. This can include any one, or on the component and, of course, the
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M7 MAINTENANCE PRACTICES ABNORMAL EVENTS
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Lightning strikes usually travel rearward from the initial lightning strike touch point on the fuselage and the engine nacelle surfaces aft of the engine inlets. Cases have occurred where airplane components have become strongly magnetized due to a lightning strike. It is possible that a lightning strike discharge could send a heavy electrical current through the metal airframe structure. This electric current creates a magnetic field and magnetizes components. Possible internal damage to the airplane due to lightning strike could be to electrical power systems and external light wire. While the electrical system is designed to be resistant to lightning strikes, a high intensity lightning strike could damage these components: S Fuel Valves S Generators S Power Feeders S Electrical Distribution Systems
The most likely areas for lightning strikes are the fuselage nose section and trailing-edge tips. The external components most likely to be hit are listed below: S Nose Radome S Nacelles S Wing Tips S HorizontaL Stabilizer Tips S Elevators S Vertical Fin Tips S Ends of the Leading Edge Flaps S Trailing Edge Flap Track Fairings S Landing Gear S Water Waste Masts S Pitot Probes S External Lights.
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General Aircraft use all necessary and known types of lightning strike protection. The basic protection is the almost all-metal external structure. The external structure acts as a shield which protects the internal areas from lightning strike. Also, the external structure protects the electrical systems and wiring from electromagnetic interference. If the airplane is hit by lightning, the following actions must be carried out: 1. A general walk-round inspection of the airplane to find the areas of the strike and discharge. 2. If signs of damage are found, carry out a detailed inspection of the damaged area to establish the amount of damage. Lightning strikes usually result in two types of damage: S Direct Damage - Surface is burned, melted or shows signs of metallic distortion at two or more attachment points. S Indirect Damage - Large electrical transients on the wiring which might cause damage to electrical systems equipment. If a lightning strike has caused a system malfunction, a full inspection of that defective system must be carried out. A lightning strike will usually cause small circular melt marks approximately 1/8 inch in diameter. The melt marks may be confined to one area or may be randomly placed over a large area. Holes with a 1/4 inch diameter or greater are possible if a high intensity lightning strike occurs. Other signs of lightning strike might be burnt or discoloured skins and rivets. The lightning strike conditional inspection covers these areas: S External Surfaces S Static Dischargers S Fuel System Valves S Integrated Drive Generator (IDG) and Related Wires S Hydraulic Fittings in the Tail Section S Radio Systems S Navigation Systems S Bonding Jumpers
LIGHTNING STRIKE
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Figure 322
Typical Lightning Strike Areas
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HIRF Protection Aircraft have been required to comply with HIRF requirements since early 1992. They have therefore been certificated to various HIRF standards, which range from no requirement through to the current policies and standards. The basic concern for better identification and protection from HIRF has arisen for the following reasons: A. Operation of modern aeroplanes is increasingly dependent upon electrical/electronic systems, which can be susceptible to electromagnetic interference. B. The increasing use of non--metallic materials like carbon or glass fibre in the construction of the aeroplane reduces their basic shielding capability against the effects of radiation from external emitters. C. Emitters are increasing in number and in power. They include ground-based systems (military systems, communication, television, radio, radars and satellite uplink transmitters), as well as emitters on ships or other aircraft. Modifications to aircraft should be assessed by the manufacturer for the effects that could be caused by exposure to HIRF, irrespective of the original certification basis. New aircraft designs must be tested, before being certified, against electromagnetic penetration. If a problem is identified, the aircraft must be redesigned to effectively reduce the intensity level of the penetrating fields.
Introduction Modern aircraft use digital control systems to perform critical functions. Such control units installed on aircraft are vulnerable to external phenomena such as high intensity electromagnetic fields. Electromagnetic interference from external sources can cause an upset of the digital system’s control unit and major damage to the aircraft.
HIGH INTENSITY RADIATED FIELDS (HIRF)
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Figure 323
Radiation Source
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High Drag/Side-Load Landing A high drag/side-load landing occurs if the airplane makes a landing with one or more of the following conditions: S The airplane skidded or overran the prepared surface S The airplane made a landing short of the prepared surface S The airplane made a landing and two or more tyres were blown S The airplane skidded on the runway sufficiently to make you think damage occurred.
Hard Landing The hard landing procedure is for hard landings at or below the maximum design landing weight limits. The pilot is responsible for making the decision whether a structural inspection is necessary. If the landing is also overweight, the Overweight Landing Inspection, not the Hard Landing Inspection, must be done.
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When the conditional inspection tells you to examine a component, check for the following faults and replace or repair components (if necessary): S Cracks S Pulled-apart structure S Loose paint (paint flakes) S Twisted parts (distortion) S Bent components S Fastener holes that become enlarged or elongated S Loose fasteners S Fasteners that have pulled out or are missing S Delaminations S Misalignment S Interference S Other signs of damage.
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General The inspection is divided into two phases. The Phase I inspection is applicable when a Hard Landing or a High Drag/Side Load Landing occurs. If the inspection during Phase I does not indicate that damage has occurred, no further inspections are necessary. If, however, the Phase I inspection indicates that damage has occurred, the Phase II inspection is necessary.
HARD LANDING
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Figure 324
Hard Nose Gear Contact
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NOTE:
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SEVERE TURBULENCE IS IDENTIFIED AS TURBULENCE WHICH CAUSES LARGE, ABRUPT CHANGES IN ALTITUDE AND/OR ATTITUDE. THE AIRPLANE COULD BE OUT CF CONTROL FOR SHORT PERIODS. IT USUALLY CAUSES LARGE VARIATIONS IN AIRSPEED. PASSENGERS AND CREW ARE MOVED VIOLENTLY AGAINST THEIR SEAT BELTS AND LOOSE OBJECTS ARE MOVED AROUND THE AIRPLANE.
General The data that follows applies to a severe or unusual turbulence condition.
Severe or Unusual Turbulence. Stall. Buffet. or Speeds in Excess of the Design Limits Conditional Inspection
OVERLIMIT INSPECTION
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General The structural inspection in this task is applicable after a severe turbulence or buffet condition. It also applies to stalls (after the initial buffet or stick shaker condition) or airplane speeds above the design speed. When the conditional inspection tells you to ”examine” a component, look for these conditions (replace or repair components, if it is necessary). S Cracks S Pulled apart structure S Loose paint (paint flakes) S Twisted parts (distortion) S Bent components S Wrinkles or buckles in the structure S Fastener holes that became larger or longer S Loose fasteners S Fasteners that have pulled out or are missing S Delaminations (a component with one or more Layers pulled apart) S Parts that are not aligned correctly S Fibre breakouts S Misalignment S Interference (clearance that is not sufficient between the parts) S Discoloration (heat damage) S Nicks or gouges S Other signs of damage.
SEVERE OR UNUSUAL TURBULENCE
M7 MAINTENANCE PRACTICES ABNORMAL EVENTS
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M7 MAINTENANCE PRACTICES ABNORMAL EVENTS
Figure 325
Example of Designed-In Safety Factors
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M 7.20 MAINTENANCE PROCEDURES
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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Non-Customized Manuals but Type-Effective Other manuals are non--customized, but type effective. This means that the content belongs to the whole fleet of that type. SRM Structural Repair Manual TSM Trouble Shooting Manual EIPC Engine Illustrated Parts Catalogue PBM Power Plant Build--Up Manual EM Engine Manual ARM Aircraft Recovery Manual SSM System Schematics Manual FIM Fault Isolation Manual FRM Fault Reporting Manual
Customized Manuals The following manuals are supplied to the customer, they are type-effective and reflect the customers configuration. AMM Aircraft Maintenance Manual MM Maintenance Manual IPC Illustrated Parts Catalogue AIPC Aircraft Illustrated Parts Catalogue WDM Wiring Diagram Manual
TYPES OF MANUALS
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Non-Customized Manuals but not Type-Effective These manuals are non--customized and not type-effective. They contain cross-references, typical procedures and standard information. CMM Component Maintenance Manual NDT Non--Destructive Testing Manual SM Standards Manual SPM Standard Practice Manual TEM Illustrated Tool and Equipment Manual WBM Weight and Balance Manual SOPM Standard Overhaul Practice
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General Aircraft Manuals are prepared by the manufacturers, eg Boeing Commercial Airplane Company or Airbus Industries, in accordance with the Air Transport Association of America Specification Number 100: S ATA 100 - Specifications for Manufacturers’ Technical Data. This specification is the industry’s recommended format and contains standards for technical manuals written by aviation manufacturers and used by airlines and others within the aviation industry.
AIRCRAFT MANUALS
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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The subject matter in each manual is divided into chapters and groups of chapters to facilitate the location of information by the user. This chapterisation provides a functional breakdown of the entire airplane. Information on all units comprising a system will be found in the chapter identified by the name of that system, or by a general name indicative of the several systems which may be covered in that chapter. Thus, all units relating to the generation and distribution of electrical power are covered in Chapter 24 ELECTRICAL POWER, while electrically-driven pumps and valves serving the fuel system are covered in Chapter 28 FUEL. All units in the elevator control system, which includes hydraulic, mechanical and electrical units are included in Chapter 27 FLIGHT CONTROLS.
MANUAL ARRANGEMENT
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Time Limits Dimensions and Areas Lifting and Shoring Levelling and Weighing Towing and Taxing Parking and Mooring Required Placards Servicing Processes And Procedures
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AIRFRAME SYSTEMS 20 General 21 Air Conditioning 22 Autopilot 23 Communications 24 Electrical Power 25 Equipment and Furnishings 26 Fire Protection 27 Flight Controls 28 Fuel 29 Hydraulic Power 30 Ice And Rain Protection 31 Instruments 32 Landing Gear 33 Lights 34 Navigation 35 Oxygen 36 Pneumatic 37 Vacuum 38 Water and Waste
AIRCRAFT 5 6 7 8 9 10 11 12 13
ATA 100 (CHAPTER AND TITLE)
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES Electronic Panels And Multi-Purpose Airborne Auxiliary Power
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For detailed usage of each manual, refer to the INTRODUCTION section in the appropriate manual.
POWER PLANT 70 Engine Standard Practices 71 Power Plant General 72 Engines 73 Engine and Fuel Control 74 Ignition 75 Air 76 Engine Controls 77 Engine Indicating 78 Exhaust 79 Oil 80 Starting 81 Turbines 82 Water Injection 83 Accessory Gear Boxes
PROPELLERS / ROTOR 60 Propellers and Rotors Standard Practice 61 Propellers 65 Rotors
STRUCTURES 51 Structure General 52 Doors 53 Fuselage 54 Nacelles and Pylons 55 Stabilizers 56 Windows 57 Wings
39 49
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Temporary Revisions Temporary revisions, printed on yellow paper, will be issued as necessary to alert the customer of configuration differences and to provide temporary instructions prior to the next scheduled revision.
Revisions Revision service to these manuals will be issued frequently. Pages that are revised will be so indicated on the list of effective pages by an asterisk (*) and identified by both a date and a page code. On each individual page, the revised area is indicated by a revision bar on the left margin.
LIST OF EFFECTIVE PAGES A list of effective pages is provided in each printed manual. The list is in numerical order and is located at the beginning of the chapter. The pages are identified at the lower outside corner by the words: “List of Effective Pages and are numbered separately, starting with page 1“
REVISION SERVICE
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SUBJECT NUMBERING The chapters of the Maintenance Manual are broken down into sections and subjects. They are numbered in a three--part subject--numbering system. S The first number in the subject number is the CHAPTER number and serves to identify the major functional system. S The middle part of the number is the SECTION number and serves to identify all of the coverage pertaining to a particular system, subsystem or group of related assemblies, including all items that are functionally a part of the system or related assemblies. S The last part of the number is the SUBJECT number and serves to identify all information relative to a specific unit, minor assemblies, simple system or simple circuit. Complete system information is included in subjects, identified by the third part of the subject number being a number. The descriptions of items which comprise the system or sub-system are also included with complete system information to the extent necessary for understanding how they work in performing their function within the system. In those cases where the items are sufficiently complex, additional description and operation type information is given at item level.
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TOPIC OR SUB--TOPIC Description and Operation Troubleshooting Maintenance Practices Servicing Removal and Installation Adjustment / Test
PAGE BLOCK 1 to 100 101 to 200 201 to 300 301 to 400 401 to 500 501 to 600
The page blocks for these topics and sub--topics are as follows:
The sub--topics are: S Servicing S Removal and Installation S Adjustment Test S Inspection Check S Cleaning and Painting S Approved Repairs.
The topics are: S Description and Operation S Troubleshooting and Maintenance Practices.
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PAGE IDENTIFICATION The four elements of page identification are (located at the lower page margin): S Chapter--Section--Subject Number S Page Number S Page Data S Page Code Number The subjects are divided into reasonably small topics and sub--topics to enable the user to locate the desired information more rapidly.
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General The Maintenance Manual contains the information necessary to enable the mechanics to service, troubleshoot, functionally check and repair all systems and equipment installed in the aircraft. It includes information necessary for the mechanic to perform maintenance procedures or make minor repairs to any item on the aircraft either on the line or in a maintenance hangar. It also covers the configuration of the aircraft as delivered to the customer. The Maintenance Manual does not contain information relative to work normally performed on items or assemblies removed from the aircraft.
MM MAINTENANCE MANUAL
AMM AIRCRAFT MAINTENANCE MANUAL
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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INDEX SYSTEM The Numerical Index is a complete alpha--numerical listing of all part numbers contained in the Detailed Parts List of the Illustrated Parts Catalogue. The index is divided into two sections : S Numerical Index -- Alpha S Numerical Index -- Numeric. The Numerical Index also displays substitution information on interchangeable standard part numbers. The Specification Cross Reference Index is divided into two sections and is common to all customers. S The first section is titled ”Specification Number Sequence”, cross-referencing the Manufacturer Specifications to the vendor part number and vendor code. S The second section is titled ”Vendor Part Number Sequence”, cross--referencing the vendor part number and code to the Manufacturer specification. The Aircraft Customer Manufacturing and Registry Number Index relates the effectivity code shown in the Detailed Parts List to the corresponding: S aircraft effectivity number S manufacturing number S and registry number. The Vendors Name and Address Index, with supply codes, is a list of vendors referenced in the Detailed Parts List and is common to all customers. The list is arranged in vendor code number sequence. The Major Drawing Number Index is an indentured breakdown denoting only the major aircraft sections and system installation drawing numbers.
SUBJECT NUMBERING The subject numbering is the same as for the Maintenance Manual.
The Illustrated Parts Catalogue contains information for use in provisioning, requisitioning, storing and issuing replaceable aircraft parts and in identifying parts.
AIPC AIRCRAFT ILLUSTRATED PARTS CATALOGUE
IPC ILLUSTRATED PARTS CATALOGUE
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Component Maintenance Manuals For Specific Items A revision service is provided in accordance with the purchase agreement between the manufacturer and the customer. Each Component Maintenance Manual for a specific item comprises : S A title page S A record of revisions S A record of temporary revisions S A list of effective pages S A list of temporary revisions S A service bulletin list S A list of approved repairers S A list of materials S A table of contents.
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Component Maintenance Sheet (CMS) This document is applicable to small items for which no CMM is required. The component maintenance sheet will include the following : S Description S Characteristics of the item S Diagram S Fits and clearances S Testing S Storage instructions S Illustrated parts list.
The Component Maintenance Manual contains all necessary information for the description and operation, disassembly, cleaning, inspection/check, repair, assembly, fits and clearances, testing and fault isolation, storage instructions and the illustrated parts list of the component. This information allows overhaul of the units, after their removal from the aircraft, in specialized workshops.
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General The Manual describes maintenance of a component in the workshop. It does not describe maintenance of the component when it is installed in the aircraft. This manual contains technical data, maintenance and repair procedures for components. The data and figures of component parts are given a separate IPC. The Aircraft Manufacturer’s Component Maintenance Manual is comprised of: S A record of revisions S A letter of transmittal S A list of effective pages not exclusive to topics corresponding to overhaulable units S An introduction S A list of chapters S An alpha--numerical index S A tab divider per chapter S A table of contents per chapter S A Component Maintenance Manual for specific items and a Component Maintenance Sheet for specific items.
COMPONENT MAINTENANCE MANUAL (CMM )
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The Table Of Contents The table of contents gives a list of Component Maintenance Manual and CMS for specific items, classified in ascending numerical order according to their ATA 100 reference.
The Alpha--Numerical Index This is the alpha--numerical index of items having a specific Component Maintenance Manual or CMS within the document. It comprises two columns : S The first column gives the part number of the item classified alpha--numerically, S and the second, the references of the corresponding manuals.
How to use the CMM and CMS Using the ATA reference, the manuals are classified inside the chapters in ascending numerical order. Using the unit reference, identify the ATA manual reference in the alpha--numerical index.
23 25 27 28 30 32 33 34 36 49 52 53 55 56 57 76
Communications Equipment and furnishings Flight controls Fuel Ice and rain protection Landing gear Lights Navigation Pneumatic Airborne aux. power Doors Fuselage Stabilizers Windows Wings Engine control
List Of ATA Chapters
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General The CMM and CMS are classified into systems (Chapters) and sub--systems (Sections), each item being identified by a part number (P/N) and assigned an ATA 100 reference. Information concerning all items of a system are identified by the reference of that system, eg System (Chapter), 27 -- Flight Controls. In each system, the information concerning all items of a sub--system are identified by the reference of that sub--system. Thus, all components relating to the ailerons and tabs of system (Chapter) 27 --Flight Controls are included in sub--system (Section) 10 -- Aileron and Tab.
IDENTIFICATION OF THE CMM/CMS
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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301 and on
401 and on
501 and on
DISASSEMBLY General Equipment and Materials List of Procedures Procedure
CLEANING Equipment and Materials Procedure
CHECK General Procedure
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601 and on
101 and on
TESTING AND FAULT ISOLATION General Equipment and Materials Procedure
REPAIR General Equipment and Materials Normal Repair Special Repair
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SPECIAL TOOLS, FIXTURES and EQUIPMENT 901 and on Special Tools, Fixtures and Equipment List
ASSEMBLY General Equipment and Materials List of Procedures Procedure Storage after Assembly
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DESCRIPTION AND OPERATION General Description and Operation
INTRODUCTION General Revision Service List of Abbreviations
SECTION PAGE BLOCK NUMBERING
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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JAA/FAA Maintenance Review Board (MRB) Service Bulletins (SB)* Service Letters (SL)* JAA/FAA Airworthiness Directives (AD’s)*.
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The scheduled maintenance tasks in this document should not be considered as all--inclusive. Each individual airline has final responsibility to decide what to do and when to do it, except for those maintenance requirements identified as ”Airworthiness Limitations” (AWL‘s) or ”Certification Maintenance Requirements” (CMR’s).
S AIRCRAFT -- i.e. A340 / B747 etc S ENGINES -- i.e. P&W PW4000 / RR Trent 500 etc.
The manufacture’s recommended scheduled maintenance tasks outlined in this document are applicable to current production and existing aircraft as follows:
* NOTE:IF MANDATORY ACTION TERMINATES THE PERIODIC MAINTENANCE TASK WITHIN APPROXIMATELY 18 MONTHS, THEN THE TASK IDENTIFIED IN THE SB, AD OR SL IS NOT INCLUDED IN THE MPD.
S S S S
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Temporary requirements in the form of Service Letters, Service Bulletins and Airworthiness Directives are the responsibility of the individual airline to incorporate. Maintenance tasks recommended in engine, APU and vendor manuals should also be considered.
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MPD General The Maintenance Planning Data (MPD) document provides maintenance planning information necessary for each aircraft operator to develop a customized scheduled maintenance program. This document lists all manufacturer-recommended scheduled maintenance tasks and satisfies (in part) the Federal Aviation Administration (FAA) and Joint Aviation Authorities (JAA) requirement that a manufacturer provide ”instructions for continued airworthiness” as specified in FAR 25. Periodic (scheduled) maintenance tasks outlined in this document may include, but are not limited to, the following sources:
MAINTENANCE PLANNING DATA
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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VENDOR MANUALS
MAINTENANCE MANUAL
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
Figure 326
SERVICE BULLETINS
SERVICE LETTERS
CARDS
JOB
VOL 1
MAINTENANCE REQUIREMENTS REVIEW & PROPOSAL DOCUMENT
Maintenance Steering Group (MSG-3)
AIRCRAFT MAINTENANCE PROGRAMME
(MPD)
INDEXES
&
MAINTENANCE PLANNING DOCUMENT
AIRLINES
MANUFACTURER
TASK CARDS
MSG-3 AIRLINE/ MANUFACTURER MAINTENANCE PROGRAM PLANNING DOCUMENT ATA
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VOL 3 JAA/FAA
MAINTENANCE REVIEW BOARD REPORT
VOL 7 VOL 6
JAA / FAA
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Certification Maintenance Requirements (CMRs) A few maintenance requirements in the Systems Section were developed as a result of the safety analysis for certification of the aircraft. These tasks, called ”Certification Maintenance Requirements” (CMRs), are identified with a hash sign (#) placed under the frequency of the specific task. Airworthiness Limitations and Certification Maintenance Requirements is the approved document that lists all CMRs for the aircraft type. This section of the document is controlled separately from the rest of the MPD and is approved by the relevant authorities and is released as a separate document. Prior to MSG--3, scheduled maintenance programs were developed from analysis which began at the component level. The effect of failures in these components was considered and, where appropriate, scheduled maintenance tasks were assigned. Using such an approach, an inclusive list of component level ”Maintenance Significant Items” (MSIs) was generated from the initial list of items subjected to analysis. Components which had no scheduled maintenance were assigned the ”Condition Monitoring” maintenance process category and were considered candidates for a reliability program.
Maintenance Steering Group (MSG-3) Most of the scheduled maintenance tasks outlined in this planning document were developed using the process guidelines of the ATA Airline/Manufacturer Maintenance Program Development Document:- MSG--3. In addition, this document includes all scheduled maintenance tasks recommended by the manufacturer (with the exception of temporary requirements as described in Section A) based on world-wide fleet service experience. There are no additional sources of the manufacturer-recommended scheduled maintenance tasks. Some structural inspection requirements arise from aircraft type certification activities with the FAA and JAA. These are identified as ”Airworthiness Limitations” and are specified in the MPD. The inspection requirements for these ”Airworthiness Limitations” are covered in the Structural Inspection Program. Also included in the MPD of an aircraft type are a list of the Structural Safe--Life Parts.
SCHEDULED MAINTENANCE PROGRAM DEVELOPMENT
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
Figure 327
SERVICE BULLETINS
SERVICE LETTERS
CARDS
JOB
VOL 1
MAINTENANCE REQUIREMENTS REVIEW & PROPOSAL DOCUMENT
Maintenance Steering Group (MSG-3)
AIRCRAFT MAINTENANCE PROGRAMME
(MPD)
INDEXES
&
MAINTENANCE PLANNING DOCUMENT
AIRLINES
MANUFACTURER
TASK CARDS
MSG-3 AIRLINE/ MANUFACTURER MAINTENANCE PROGRAM PLANNING DOCUMENT ATA
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VOL 3 JAA/FAA
MAINTENANCE REVIEW BOARD REPORT
VOL 7 VOL 6
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C-Check There are also two different C--Check intervals specified for Boeing 757 maintenance. These are identified in the interval column of the Systems, Structural and Zonal programs. S The Systems (including lubrication) and Zonal C--Check interval is 6,000 flight hours or 18 months, whichever comes first. The Systems/Zonal C--Check is designated ”1C”. No multiple C--Check intervals should be escalated until at least one aircraft inspection has been accomplished at 12,000 flight hours for 2C items, 18,000 flight hours for 3C items and 24,000 flight hours for 4C items. S The Structures C--Check interval is 3,000 flight cycles or 18 months, whichever comes first. The Structures C--Check is designated ”S 1C”. Some structures tasks have a calendar limit interval instead of the normal letter check interval described above. The following provides an explanation for the interval difference.
A-Check There are two different A--Check intervals specified for Boeing 757 maintenance. These are identified in the interval column of the Systems, Structural,and Zonal programs. S The Systems (including lubrication) and Zonal A--Check interval is 500 flight hours. The Systems/Zonal A--Check is designated ”1A”. S The Structural A--Check interval is 300 flight cycles and is designated ”S 1A”.
Transit Check The Transit Check (TC) is intended to assure continuous serviceability of a transiting aircraft. This check is planned for use at an en-route stop and is basically a ”walk--around” inspection which requires a check of both the aircraft interior and exterior for obvious damage, leaks, correctly operating equipment, security of attachments and required servicings.
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C-Check (cont..) The original Maintenance Review Board Report (MRBR) S 1C interval was 3,000 flight cycles or 15 months (whichever came first) and the S 2C, S 3C and S 4C intervals were multiples thereof. A revision of the MRBR (issued 11/90), was based on current accumulated service experience. The MRBR calendar time limit for S 1C, S 2C, and S 3C was escalated to 18, 36 and 54 months respectively with the S 4C remaining at 60 months. However, based on fleet--wide corrosion findings, the initial (starting point) interval for a selected number of structural inspection tasks was kept at 15, 30, and 45 months. Consequently, the MRBR interval for these tasks was changed from S1C, S 2C and S 3C to 3,000 cycles/15 months, 6,000 cycles/30 months and 9,000 cycles/45 months, respectively. The interval for any of these calendar-based tasks (15, 30, 45 or 60 months) can be adjusted, as with any other structural inspection task, by an operator, based on their service experience as noted in the Maintenance Program Rules and Operating Rules of the MRBR. The Systems Maintenance and Zonal Inspection Programs are flight-hour sensitive; whereas, the Structural Inspection Program is flight cycle or calendar time sensitive. Separation of these A and C check definitions provides an operator with maximum flexibility in scheduling and packaging the systems/structural/zonal tasks based on aircraft utilization. The table opposite summarizes the Basic Maintenance Check Intervals applicable to the Boeing 757. The maintenance program utilizing these check intervals is intended for normal aircraft/airline daily utilization. Task intervals are expressed in hours, cycles, calendar time or a letter check. Individual operators may convert intervals (based on aircraft utilization) to their desired units provided such conversion does not result in exceeding the frequencies identified herein. An operator may package any or all of the tasks not specified at one of the basic check intervals into one of the basic checks, provided such packaging does not exceed the interval shown for the task.
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General Many of the scheduled maintenance tasks listed in the MPD document are to identify the frequency of accomplishment in terms of a letter check, eg 1A, 2A, 1C, etc. These letter checks and the other checks are defined as follows.
MAINTENANCE CHECKS
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Figure 328
PRIOR TO FLIGHT 500 FLIGHT HOURS 300 FLIGHT CYCLES 6,000 FLIGHT HOURS OR 18 MONTHS * 3,000 FLIGHT CYCLES OR 18 MONTHS * 12,000 FLIGHT CYCLES OR 72 MONTHS *
1 TRANSIT CHECK (TR) 1 A--CHECK (SYSTEMS/ZONAL) 1 A--CHECK (STRUCTURES) 1 C--CHECK (SYSTEMS/ZONAL) 1 C--CHECK (STRUCTURES) 1 4C--CHECK (STRUCTURES)
Maintenance Checks
*whichever comes first
INITIAL INTERVALS
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Modification Whenever a UK--registered aircraft (or an engine, or propeller fitted to such an aircraft) is modified, the Certificate of Airworthiness is invalidated until such time as the modification is approved by the CAA (either directly or through the procedures of an organisation approved by the CAA for the purpose).
Type Certificate Certification of the design of an aircraft is normally declared by the granting of a Type Certificate, for which a pre--requisite will be Type Certification of any engines and/or propellers fitted. Subject to compliance with any additional requirements that may be imposed, an aircraft that conforms with the type certificated design will be eligible for a Certificate of Airworthiness.
Certificate of Airworthiness The internationally-recognised standard for the airworthiness of a civil aircraft is a Certificate of Airworthiness issued in accordance with the Convention on International Civil Aviation (ICAO Chicago Convention). An aircraft which cannot show compliance with the standards required for the award of a Certificate of Airworthiness, but nevertheless can be considered airworthy (subject to specified limitations), may be granted a Permit to Fly. To qualify for a Certificate of Airworthiness the design of an aircraft must be shown to comply with appropriate design standards, and the individual aircraft must be shown to have been constructed in conformity with the approved design.
Introduction A modification is any change to the design of a product.
MODIFICATION PROCEDURES
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Once the stores inspector is satisfied he will issue a Release Voucher and transfer the part to the Bonded Store. A register is kept detailing all Release Vouchers that have been issued. This contains details of the component and the identity of the issuer. Parts and components are issued from the Bonded Store to be installed onto the aircraft. Part of the release voucher is returned to the stores with the removed item. Information from the returned voucher will have been completed by the mechanic or engineer installing the new part. This information is used by Technical Records to track the part and serial number of components installed on a particular aircraft.
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Stores and Supplies Procedures Systems must be in place to ensure that parts and materials used in the maintenance of aircraft are approved parts and conform to the required specifications. It is obvious that there are significant safety implications if parts are installed that are bogus or have not been correctly repaired. Parts and materials must come from organizations that are approved by the National Airworthiness Authority (NAA). These organizations can be aircraft manufacturers, original equipment manufacturers (OEM), approved repair organizations and authorized material suppliers. To make sure that parts and materials are examined before being cleared for use on aircraft, stores premises and procedures are designed with this protection in mind. All parts and material enter the engineering organization stores system through “Goods Inwards“ into a Quarantine Store. A certificate indicating that the item comes from an approved source must accompany all components, parts and assemblies. In JAA member states this certificate is the “JAA Form One“. Parts originating in the USA may have an equivalent “FAA Form 8130“. Other approved forms are the Canadian TCA Form 24--0078 or specific “Authorized Release Tags“ acceptable to the NAA. Standard parts, i.e. nuts, bolts, washers, diodes etc, which are manufactured to a common standard and are designated by the Type Certificate Holder or Design Authority do not require an Authorized Release Tag and must be accompanied by a Certificate of Conformity. All material and parts must be logged in a Register of Quarantined Items. The stores inspector then examines every item, checking details from the JAA Form One (Part Number, Serial Number etc) against the component or part. Parts are also examined for general condition, that they have not been damaged in transit and that transport blanks are in place etc. Parts that fail this inspection remain in the quarantine stores and must be returned to the supplier as soon as possible. Regular checks of the Quarantine Register are carried out to ensure parts failing to conform to specification do not remain in the store.
STORES PROCEDURES
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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Goods Inwards
OIL
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
Figure 329
Bonded Store
Store and Supplies Procedures
Quarantine Store
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Aircraft
Page: 713
M7.20 (Cat A)
IR PART 66
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A certificate of release to service is issued by the appropriately authorised certifying staff on behalf of the JAR--145 approved maintenance organisation once he is satisfied that all maintenance required by the customer of the aircraft or aircraft component has been properly carried out. An aircraft component which has been maintained off the aircraft requires: S the issue of a certificate of release to service for such maintenance and S another certificate of release to service in regard to being installed properly on the aircraft when such action occurs. A certificate of release to service must contain: S basic details of the maintenance carried out S the date such maintenance was completed and S the identity (including approval reference) of the JAR 145-approved maintenance organisation and certifying staff issuing such a certificate.
CERTIFICATION/RELEASE PROCEDURES
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M7.20 (Cat A)
IR PART 66
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Figure 330
Sample: Release-To-Service Certificate
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M7.20 (Cat A)
IR PART 66
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A JAR--145 approved maintenance organisation will have a quality policy for that organisation. It will have established procedures to ensure good maintenance practices and compliance with all relevant requirements in JAR--145 (Approved Maintenance Organisations). The organisation will have established a quality system that includes: S Independent audits in order to monitor compliance with required aircraft/ aircraft component standards and adequacy of the procedures to ensure that such procedures invoke good maintenance practices and airworthy aircraft/aircraft components. S A quality feedback reporting system to the person or group of persons specified in JAR 145.30(a) and ultimately to the accountable manager that ensures proper and timely corrective action is taken in response to reports resulting from the independent audits.
MAINTENANCE INSPECTION/QUALITY CONTROL/QUALITY ASSURANCE
M7 MAINTENANCE PRACTICES MAINTENANCE PROCEDURES
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M7.20 (Cat A)
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M7.20 (Cat A)
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A JAR--145 approved maintenance organisation must record all details of work carried out in a form acceptable to the JAA full member Authority. It must provide a copy of each certificate of release to service to the aircraft operator, together with a copy of any specific approved repair/modification data used for repairs/modifications carried out. It must retain a copy of all detailed maintenance records and any associated maintenance data for two years from the date the aircraft or aircraft component to which the work relates was released from the organisation.
MAINTENANCE RECORDS
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M7.20 (Cat A)
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M7.20 (Cat A)
IR PART 66
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Primary Maintenance There are three types of primary maintenance processes practised today. 1. Hard Time. This is a preventative process in which known deterioration of an item is limited to an acceptable level by the maintenance actions which are carried out at periods related to time in service (eg calendar time, number of cycles, number of landings). These actions normally include S servicing S overhaul S partial overhaul and S replacement. This process is applied to an item when S the failure of the item has a direct adverse effect on airworthiness and where evidence indicates that it is subject to wear or deterioration S there is a hidden function which cannot be checked with the item in-situ S wear or deterioration exists to such an extent that a time limit is economically desirable S component condition or ’life’ progression sampling is practised, and S limitations are prescribed in a Manufacturer’s Warranty.
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IR PART 66
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2. On-Condition. This is also a preventative process but one in which the item is inspected or tested, at specified periods, to determine whether it can continue in service. On-Condition philosophy is to remove an item before it fails, not ’fit until failure’ or ’fit and forget it’. 3. Condition Monitoring. This process is one in which information on items gained from operational experience is collected, analysed and interpreted on a continuing basis as a means of implementing corrective procedures. It is applied to items whose failure does not have a direct adverse effect on operating safety and no adverse age reliability relationship has been identified.
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Introduction This section gives general information on the concepts and practices of aircraft maintenance control by the use of Condition Monitored Maintenance. Confidence in continued airworthiness has long been based on the traditional method of maintaining safety margins by the prescription of fixed component lives and by aircraft ’strip-down’ policies. However, there has been a need for change to this basic philosophy of aircraft maintenance, influenced by S the economic state of the industry S changes in aircraft design philosophy, and S progress in engineering technology.
CONTROL OF LIFE-LIMITED COMPONENTS
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Figure 331
Time to Change
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M7.20 (Cat A)
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M7.20 (Cat A)
IR PART 66
1
66 67 69 71
M7.3 TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PUNCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAWING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAW BLADE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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FILE SHAPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
75
21 21 21 21 23 25 25 29 39 45 55 57
TOOL HUSBANDRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TOOL CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TOOL CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STANDARDS OF WORKMANSHIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . USE OF WORKSHOP MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . DIMENSIONS, ALLOWANCES & TOLERANCES . . . . . . . . . . . . . . . . . GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MEASUREMENT UNIT SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RULES AND SCALES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SQUARES AND GAUGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BALL GAUGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MARKING OUT AND TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FILING
20
3 5
M 7.2 WORKSHOP PRACTISES . . . . . . . . . . . . . . .
PERSONAL SAFETY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FIRE--GENERAL PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M7.1 SAFETY PRECAUTIONS AIRCRAFT AND WORKSHOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
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99 99 105
DRILL GRINDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DRILLING SAFETY PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
107 111 115 117
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DEBURRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . COMMON DRILLING PROBLEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WORK CLAMPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page i
119 121 123 127
DRILLING WORK SEQUENCE . . . . . . . . . . . . . . . . . 119
STATIONARY DRILL MACHINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HAND-HELD DRILL MOTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HAND DRILL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE CHUCK OF A DRILL MACHINE . . . . . . . . . . . . . . . . . . . . . . . . . . .
TYPES OF DRILL MACHINES . . . . . . . . . . . . . . . . . 107
91 93 95
91
DRILLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TWIST DRILL NOMENCLATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DRILL TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
79 79 81 83 85 87 89
FILE CUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GRADE OF CUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PROPER WORKING POSITION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FILE TECHNIQUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FILING OF RADII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DRAW FILING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CLEANING DIRTY FILES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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145
163 163 167 169 173 183 195
199 201 211 213
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THREAD FORMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THREAD PITCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HAND THREADING TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HAND TAPPING TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPE OF TAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
219 221 223 225 227
T H R E A D C U T T I N G . . . . . . . . . . . . . . . . . . . . . 218
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . COUNTERSINKING TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GUIDELINES FOR COUNTERSINKING . . . . . . . . . . . . . . . . . . . . . . . . . COUNTERSINK CUTTING AGENTS / SPEEDS . . . . . . . . . . . . . . . . . .
C O U N T E R S I N K I N G . . . . . . . . . . . . . . . . . . . . 198
LIMITS AND FITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE ISO SYSTEM OF LIMITS AND FITS . . . . . . . . . . . . . . . . . . . . . . . REAMING GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REAMER DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPES OF REAMERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REAMING SPEED AND AGENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REAMING ADVICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
R E A M I N G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DRILL SPEEDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
ADDITIONAL TOOLS FOR DRILLING . . . . . . . . . . . . . . . . . . . . . . . . . . DRILL AGENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DRILLING SIZES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DRILLING AIDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
TABLE OF CONTENTS
M7 MAINTENANCE PRACTICES
ENGINEERING DRAWINGS (GENERAL) . . . . . . . . . . . . . . . . . . . . . . . AIRCRAFT ENGINEERING DRAWINGS . . . . . . . . . . . . . . . . . . . . . . . . SCALE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TITLE BLOCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ZONES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REVISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PARTS LIST (BILL OF MATERIALS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPES AND USE OF LINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYMBOLS -- RECESSED HOLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYMBOLS -- CONVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYMBOLS -- SURFACE TEXTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PERSPECTIVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SKETCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PROJECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SECTIONAL VIEWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DIMENSIONING FROM A COMMON DATUM . . . . . . . . . . . . . . . . . . . DIMENSIONAL TOLERANCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page ii
281 281 281 283 283 283 283 285 291 293 295 297 299 299 299 303 309 311
M 7.5 ENGINEERING DRAWINGS . . . . . . . . . . . . . . 280
HOLES FOR TAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 HOW TO TAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 TORQUE WRENCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 TORQUE WRENCHES (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 MICROMETER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 VERNIER CALLIPER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 DIAL INDICATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 ABRASIVE WHEELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 LUBRICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 GENERAL LUBRICATION INSTRUCTIONS - BOEING . . . . . . . . . . . . 265 EXAMPLE: B737 LUBRICATION FITTINGS REMOVAL/INSTALLATION . . . 269 EXAMPLE: A320 MLG AND DOORS LUBRICATION . . . . . . . . . . . . . . 271 ELECTRICAL TEST EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
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SYSTEMS OF FITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FASTENERS -- HOLE AND DRILL DATA -- METALLIC STRUCTURE WEAR LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TWIST LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STANDARD METHODS FOR CHECKING SHAFTS & BEARINGS . . ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. ............................................................. .............................................................
331 339 355 357 359 362 362 362 362 362 362 362 362 362 362 362 362 362 362 362 362
M 7.6 FITS AND CLEARANCES . . . . . . . . . . . . . . . . 330
BLUEPRINT READING FUNDAMENTALS . . . . . . . . . . . . . . . . . . . . . . . DETAIL DRAWINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ASSEMBLY DRAWINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSTALLATION DRAWINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EXPLODED--VIEW DRAWING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SCHEMATIC DRAWING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ELECTRICAL WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DRAWING STORAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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367 369 375 381
389 393
401 403 403 Page iii
CRIMPING OF PIDG TERMINALS AND SPLICES . . . . . . . . . . . . . . . . CLOSED END SPLICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .............................................................
PRE INSULATED DIAMOND GRIP (PIDG) TERMINALS AND SPLICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
SOLDER SLEEVE PIGTAIL . . . . . . . . . . . . . . . . . . . . 397
CRIMPING OF CONTACTS . . . . . . . . . . . . . . . . . . . . 395
CONTACT INSERT & REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONNECTOR CONTACT CRIMPING-TOOL . . . . . . . . . . . . . . . . . . . . .
CONNECTOR TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . 389
STRIPPING WIRE AND CABLE . . . . . . . . . . . . . . . . 387
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
GENERAL NOTES (CONTINUED) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WIRE AND CABLE SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WIRE BUNDLE TIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REPAIR OF WIRE AND CABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GENERAL NOTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
SAFETY PRECAUTIONS ON AIRCRAFT . . . . . . . . 363
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411
419
421 423
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Aug 2004
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RIVETED JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UNITS OF MEASUREMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INTER-RIVET BUCKLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DIMPLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TOOLS USED FOR SOLID RIVETING . . . . . . . . . . . . . . . . . . . . . . HOLE PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HOLE PREPARATION (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . .
430 433 439 441 443 445 451 453
M7.8 RIVETING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
CONTINUITY TESTING . . . . . . . . . . . . . . . . . . . . . . . . 425
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSULATION RESISTANCE MEASUREMENT . . . . . . . . . . . . . . . . . . .
GROUNDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
BONDING RESISTANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BONDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
TERMINAL BLOCKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TERMINAL STRIPS, BLOCKS & MODULES . . . . . 409
............................................................. ............................................................. ............................................................. ............................................................. SPARE WIRE CAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CRIMPING-INSPECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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504
508 508 508 508 510 512
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BEARINGS (GENERAL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SLIDING BEARINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ANTI-FRICTION BEARINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LUBRICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BEARING DEFECTS AND THEIR CAUSES . . . . . . . . . . . . . . . . . . . . . BEARING DEFECTS AND THEIR CAUSES (CONT’D) . . . . . . . . . . . .
M 7.11 BEARINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M7.10 SPRINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
TUBES AND PIPES / TUBE ASSEMBLIES . . . . . . . . . . . . . . . . . . . . . . 470 CLAMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 FLARE-TYPE FITTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 BENDING TUBES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480 TUBE BENDING COMING UP TO REQUESTED DIMENSIONS . . . 484 TUBE BENDING COMING UP TO REQUESTED DIMENSIONS (CONT.) . . 486 TUBE BENDING COMING UP TO REQUESTED DIMENSIONS (CONT.) . . 488 TUBE BENDING COMING UP TO REQUESTED DIMENSIONS (CONT.) . . 490 HOSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494 HOSES (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496 HOSES (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498 HOSES (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
M7.9 PIPES AND HOSES
INSTALLATION PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 INSPECTION AND PERMITTED LIMITS . . . . . . . . . . . . . . . . . . . . 457 SOLID RIVET REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
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521
531
533 535
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Aug 2004
CABLE LINES (GENERAL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTROL CABLE HANDLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSPECTION OF CABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSPECTION OF PULLEYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROLLING ON TERMINALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROLLING OF SLEEVE TERMINALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROLLING OF SLEEVE TERMINALS (CONT.) . . . . . . . . . . . . . . . . . . . . INSPECTION OF MANUFACTURED CABLE LINES . . . . . . . . . . . . . . CABLE TIGHTENING AND MEASURING TENSION . . . . . . . . . . . . . . CABLE TENSIOMETER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTROL CABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TELEFLEX CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
540 542 544 546 548 550 552 554 556 556 560 562
M 7.13 CONTROL CABLES . . . . . . . . . . . . . . . . . . . . 539
EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GEARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INSPECTION OF SCREWJACKS . . . . . . . . . . . . . . . 533
EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INSPECTION OF BELTS, CHAINS AND CABLES 531
CONTROL CHAINS AND SPROCKETS . . . . . . . . . . . . . . . . . . . . . . . . .
M7.12 TRANSMISSIONS . . . . . . . . . . . . . . . . . . . . . . 520
GENERAL INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REMOVAL OF BEARINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSTALLATION OF BEARINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INSTALLATION OF ANTI-FRICTION BEARINGS . . . . . . . . . . . . . . . . . BEARINGS THAT CANNOT BE DISASSEMBLED . . . . . . . . . . . . . . . . BEARINGS THAT CAN BE DISASSEMBLED . . . . . . . . . . . . . . . . . . . .
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596 600 602 610 621
572 592 592 ...
657 661 663
650 650 650 652 654 657
627 635 635 636 638 640 642 648 648
Page v
INSPECTION OF METAL AIRCRAFT STRUCTURES . . . . . . . . . . . . . DAMAGE CLASSIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REPAIRABLE DAMAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPES OF STRUCTURAL DAMAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPES OF STRUCTURAL DAMAGE (CONTINUED) . . . . . . . . . . . . . CORROSION REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CORROSION REMOVAL (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . CORROSION ON ALUMINIUM ALLOYS . . . . . . . . . . . . . . . . . . . . . . . . REMOVAL OF CORROSION FROM CARBON STEEL . . . . . . . . . . . . CORROSION REMOVAL FROM STAINLESS STEEL AND NICKEL CHROMIUM ALLOYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CORROSION REMOVAL FROM TITANIUM ALLOYS . . . . . . . . . . . . . REMOVAL OF CORROSION FROM CADMIUM-PLATED PARTS . . TYPES OF CORROSION PROTECTION PROCEDURES . . . . . . . . . PREPARATORY TREATMENT OF SURFACES . . . . . . . . . . . . . . . . . . PAINT FINISHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PAINT FINISHES IN THE AREA OF THE CABIN/FUSELAGE OUTER SKIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PRIMER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INTERMEDIATE PRIMER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M7.18A TYPES OF DEFECT AND VISUAL INSPECTION TECHNIQUES/ CORROSION REMOVAL ASSESMENT AND REPROTECTION . 626
BOWDEN CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A/C STORAGE METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PARKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RETURN TO OPERATION (PARKING OF NOT MORE THAN 2 DAYS) PAGE: 594 PARKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STORAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STORAGE (CONT’D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AIRCRAFT REFUELLING/DEFUELLING . . . . . . . . . . . . . . . . . . . . . . . . GROUND SERVICING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . .
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LIGHTNING STRIKE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HIGH INTENSITY RADIATED FIELDS (HIRF) . . . . . . . . . . . . . . . . . . . HARD LANDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SEVERE OR UNUSUAL TURBULENCE . . . . . . . . . . . . . . . . . . . . . . . . OVERLIMIT INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MANUAL ARRANGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REVISION SERVICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MODIFICATION PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CERTIFICATION/RELEASE PROCEDURES . . . . . . . . . . . . . . . . . . . . . MAINTENANCE INSPECTION/QUALITY CONTROL/QUALITY ASSURANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MAINTENANCE RECORDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTROL OF LIFE-LIMITED COMPONENTS . . . . . . . . . . . . . . . . . . . 716 718 720
678 680 682 684 684 690 692 710 714
M7.19 ABNORMAL EVENTS . . . . . . . . . . . . . . . . . . . 677
EPOXY PRIMER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . COATING LACQUERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ELECTRICALLY-CONDUCTIVE PAINTS . . . . . . . . . . . . . . . . . . . . . . . . WATER-REPELLENT FLUID AND CORROSION INHIBITORS . . . . . DINITROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DIS--ASSEMBLY AND RE--ASSEMBLY TECHNIQUES . . . . . . . . . . . .
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Workshop and Hangar Safety . . . . . . . . . . . . . . . . . . . . . . . Typical Fuelling/Defuelling Safety Zone . . . . . . . . . . . . . . . Working with Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . Safety With Compressed Air . . . . . . . . . . . . . . . . . . . . . . . . Clean Work Containers (Fume Cabinets) . . . . . . . . . . . . . Individual and Team Lifting . . . . . . . . . . . . . . . . . . . . . . . . . Types of Fire and Relevant Extinguishers . . . . . . . . . . . . . Fighting Fires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tool Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Equipment Stores . . . . . . . . . . . . . . . . . . . . . . . . . Measurement Examples . . . . . . . . . . . . . . . . . . . . . . . . . . Measurement Of Dimensions . . . . . . . . . . . . . . . . . . . . . . Number Prefix Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . English Length System . . . . . . . . . . . . . . . . . . . . . . . . . . . Metric System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Decimal And Metric Equivalent Of Inches . . . . . . . . . . . . Flexible Scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scale Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flexible Steel Tape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Set Square . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radius Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protractor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feeler Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Blend Out Measurement Sequence . . . . . . . . . . . . . . . . . Ball (Hole) Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marking Out Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . Marking-Out Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marking-Out Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uses of Combination Set . . . . . . . . . . . . . . . . . . . . . . . . . . Punches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saw Blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . File Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . File Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35
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Figure 36 Figure 37 Figure 38 Figure 39 Figure 40 Figure 41 Figure 42 Figure 43 Figure 44 Figure 45 Figure 46 Figure 47 Figure 48 Figure 49 Figure 50 Figure 51 Figure 52 Figure 53 Figure 54 Figure 55 Figure 56 Figure 57 Figure 58 Figure 59 Figure 60 Figure 61 Figure 62 Figure 63 Figure 64 Figure 65 Figure 66 Figure 67 Figure 68 Figure 69 Figure 70
File Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Working Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . File Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Filing of Radii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Draw Filing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cleaning Dirty Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Twist Drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Twist Drill Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . Drill Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Machine Spindle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding Drill Point Angles . . . . . . . . . . . . . . . . . . . . . . . . . Drill Grinding Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . Grinding Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stationary Drill Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . Pillar Drill Work Sequence . . . . . . . . . . . . . . . . . . . . . . . . . Hand-Held Drill Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Hand Held Drill Motors . . . . . . . . . . . . . . . . . . . . . Hand Drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Keyed Chuck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using The Drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deburring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pillar Drill Clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hand Drill Clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drill Stop and Drill Guide . . . . . . . . . . . . . . . . . . . . . . . . . . Nut Plate Drill Jig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hole Finder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drill Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drill Size Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RPM Table IV - 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RPM Table IV - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . RPM Table IV - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . RPM Table IV - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . RPM Table IV - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . RPM Table IV - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . Table IV - 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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80 82 84 86 88 90 92 94 96 98 100 102 104 108 110 112 114 116 118 120 122 128 130 134 136 138 140 144 146 147 148 149 150 151 152
Aug 2004
Table IV - 2 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table IV - 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table IV - 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table IV - 4 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table IV - 4 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table IV - 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table IV - 5 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Types Of Fit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ISO Fits (Hole Basis) - British Standard 4500 . . . . . . . . Table Of Defect Criteria (ATA-Chapter 51--40--05) . . . . Reamer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Space Of Cutting Edges . . . . . . . . . . . . . . . . . . . . . . . . . . Machine Reamer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hand Reamer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pilot and Pilot Chuck Reamer . . . . . . . . . . . . . . . . . . . . . . Expansion Hand Reamer and Taper Reamer . . . . . . . . . Adjustable Hand Reamer . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 1 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 2 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 2 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V- 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table V - 5 (Continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . Reaming Advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example Table Of Sheet Thickness For Countersinking Standard Countersink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Microstop Countersink . . . . . . . . . . . . . . . . . . . . Microstop Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Back Countersinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spotfacer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cutting Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Figure 71 Figure 72 Figure 73 Figure 74 Figure 75 Figure 76 Figure 77 Figure 78 Figure 79 Figure 80 Figure 81 Figure 82 Figure 83 Figure 84 Figure 85 Figure 86 Figure 87 Figure 88 Figure 89 Figure 90 Figure 91 Figure 92 Figure 93 Figure 94 Figure 95 Figure 96 Figure 97 Figure 98 Figure 99 Figure 100 Figure 101 Figure 102 Figure 103 Figure 104 Figure 105
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153 154 155 156 157 158 159 164 166 168 170 172 174 176 178 180 182 184 185 186 187 188 189 190 191 192 196 200 202 204 206 208 210 214 215
Figure 106 Thread Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 107 Screw Pitch Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 108 Hand Threading Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 109 Hand Tapping Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 110 Types of Taps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 111 Holes for Tapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 112 How to Tap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 113 Torque Wrenches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 114 Torque Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 115 Micrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 116 Reading Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 117 Reading Examples (Continued) . . . . . . . . . . . . . . . . . . . Figure 118 Micrometer Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 119 Vernier Calliper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 120 Vernier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 121 Principle of a Vernier . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................ Figure 122 Vernier Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................ Figure 123 Vernier Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 124 Vernier Reading Examples 1 . . . . . . . . . . . . . . . . . . . . . . Figure 125 Vernier Reading Examples 2 . . . . . . . . . . . . . . . . . . . . . . Figure 126 Vernier Measuring Precautions . . . . . . . . . . . . . . . . . . . . Figure 127 Dial Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 128 Dial Indicator Work Sequence . . . . . . . . . . . . . . . . . . . . Figure 129 Off-Hand Grinding Machines . . . . . . . . . . . . . . . . . . . . . . Figure 130 Lubrication Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 131 Lubrication Symbol Examples . . . . . . . . . . . . . . . . . . . . . Figure 132 B737 Main Landing Gear Lubrication Example . . . . . . Figure 133 Lubrication Fitting Modification and Installation . . . . . . Figure 134 Greaser Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 135 Greaser Table (Cont’d) . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 136 Lubrication Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 137 Electrical Test Instruments . . . . . . . . . . . . . . . . . . . . . . . Figure 138 Bond Testing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Aug 2004
SCALE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Engineering Drawing -- Standard Layout . . . . . . . . . . . . Types And Use Of Lines . . . . . . . . . . . . . . . . . . . . . . . . . Break Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Repetitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common Drawing Symbols -- Holes . . . . . . . . . . . . . . . Common Drawing Symbols -- Recessed Holes . . . . . . Typical Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Surface Texture Symbols . . . . . . . . . . . . . . . . . . . . . . . . . First Angle Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . Third Angle Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . Sectional View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PART, HALF AND STAGGERED SECTIONS . . . . . . . AUXILIARY VIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DIMENSIONING FROM A COMMON DATUM . . . . . . Dimensional Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . Detail Drawing 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detail Drawing 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assembly Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exploded - View Drawing . . . . . . . . . . . . . . . . . . . . . . . . . Schematic Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drawing Storage Methods . . . . . . . . . . . . . . . . . . . . . . . . Fits and Clearances - Fundamentals . . . . . . . . . . . . . . . Basic Types Of Fit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clearance Fit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types Of Fit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 1 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 2 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 3 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 4 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 5 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 6 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 7 . . . . . . . . . . . . . . . . . . . .
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Figure 139 Figure 140 Figure 141 Figure 142 Figure 143 Figure 144 Figure 145 Figure 146 Figure 147 Figure 148 Figure 149 Figure 150 Figure 151 Figure 152 Figure 153 Figure 154 Figure 155 Figure 156 Figure 157 Figure 158 Figure 159 Figure 160 Figure 161 Figure 162 Figure 163 Figure 164 Figure 165 Figure 166 Figure 167 Figure 168 Figure 169 Figure 170 Figure 171 Figure 172 Figure 173
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282 284 286 288 290 292 294 296 298 300 302 304 306 308 310 312 314 316 318 320 322 324 326 328 332 334 336 338 340 341 342 343 344 345 346
Figure 174 Figure 175 Figure 176 Figure 177 Figure 178 Figure 179 Figure 180 Figure 181 Figure 182 Figure 183 Figure 184 Figure 185 Figure 186 Figure 187 Figure 188 Figure 189 Figure 190 Figure 191 Figure 192 Figure 193 Figure 194 Figure 195 Figure 196 Figure 197 Figure 198 Figure 199 Figure 200 Figure 201 Figure 202 Figure 203 Figure 204 Figure 205 Figure 206 Figure 207 Figure 208
Extracts From Airbus SRM -- 8 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 9 . . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 10 . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 11 . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 12 . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 13 . . . . . . . . . . . . . . . . . . . Extracts From Airbus SRM -- 14 . . . . . . . . . . . . . . . . . . . Outer Airbrakes - Wear Limits (A300) . . . . . . . . . . . . . . Twist Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using Dial Test Indicators . . . . . . . . . . . . . . . . . . . . . . . . Safety precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General installation (cont) . . . . . . . . . . . . . . . . . . . . . . . . Clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Clamp Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bundle Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wire bundle tying examples . . . . . . . . . . . . . . . . . . . . . . Plastic wire ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Repair of wire and cable . . . . . . . . . . . . . . . . . . . . . . . . . Wire stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rear release contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . Front release contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . Crimping Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crimping check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solder sleeve pigtails . . . . . . . . . . . . . . . . . . . . . . . . . . . . PIDG Terminals & Splices . . . . . . . . . . . . . . . . . . . . . . . . Crimping of Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . Closed End Splice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crimping spare wire caps . . . . . . . . . . . . . . . . . . . . . . . . Crimping inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . Terminal strips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Terminal blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crimping terminal block contacts . . . . . . . . . . . . . . . . . . Terminal modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Aug 2004
Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 Bonding resistance measurement . . . . . . . . . . . . . . . . . 420 Grounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 Measurement of insulation resistance . . . . . . . . . . . . . . 424 Continuity testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 Solid Rivets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 Fastener Edge Distance . . . . . . . . . . . . . . . . . . . . . . . . . 434 Dimensions for Driving Non-Fluid-Tight Solid Rivets (Boeing) . . 435 Figure 218 Grip Ranges/Recommended Lengths: Standard Aluminium Alloy Rivets (Boeing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 Figure 219 Dimensions for Driving Non-Fluid-Tight Solid Rivets (Boeing) . . 437 Figure 220 Dimensions for Driving Fluid-Tight Solid Rivets (Boeing) . . . . . . . 438 Figure 221 Standard Drill Sizes & Decimal Equivalents . . . . . . . . . 440 Figure 222 Fuel Tank Fastener Spacing . . . . . . . . . . . . . . . . . . . . . . 442 Figure 223 Dimpling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 Figure 224 Rivet Guns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 Figure 225 Rivet Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448 Figure 226 Rivet Squeezers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 Figure 227 Minimum Part Thickness for 100o Countersinking . . . 452 Figure 228 Underhead Radius/Chamfer Limits . . . . . . . . . . . . . . . . 454 Figure 229 Bucking Bars - Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 456 Figure 230 Upset Rivet Dimension (Airbus) . . . . . . . . . . . . . . . . . . . 458 Figure 231 Formed Head Defects and Limits (Airbus) 1 . . . . . . . . 459 Figure 232 Formed Head Defects and Limits (Airbus) 2 . . . . . . . . 460 Figure 233 Acceptable Limits for Cracks (Airbus) . . . . . . . . . . . . . . 462 Figure 234 Cracks Analysis: Shop Head (Boeing) . . . . . . . . . . . . . 463 Figure 235 Cracks Analysis: Non-Fluid-Tight Rivets (Boeing) . . . . 464 Figure 236 Cracks Analysis: Fluid-Tight Rivets (Boeing) . . . . . . . . 465 Figure 237 Gap Analysis: Rivet Heads/Tails (Boeing) . . . . . . . . . . 466 Figure 238 Solid Rivet Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468 Figure 239 Correct Tube Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . 471 Figure 240 Clamp Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 Figure 241 Single Flare Fittings and Tools . . . . . . . . . . . . . . . . . . . . 475
Figure 209 Figure 210 Figure 211 Figure 212 Figure 213 Figure 215 Figure 216 Figure 217
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Figure 242 Figure 243 Figure 244 Figure 245 Figure 246 Figure 247 Figure 248 Figure 249 Figure 250 Figure 251 Figure 252 Figure 253 Figure 254 Figure 255 Figure 256 Figure 257 Figure 258 Figure 259 Figure 260 Figure 261 Figure 262 Figure 263 Figure 264 Figure 265 Figure 266 Figure 267 Figure 268 Figure 269 Figure 270 Figure 271 Figure 272 Figure 273 Figure 274 Figure 275 Figure 276
Flared Fitting Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Double Flare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tube Bender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tube Bender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tube Bending to Requested Dimension 1 . . . . . . . . . . Tube Bending to Requested Dimension 2 . . . . . . . . . . Tube Bending to Requested Dimension 3 . . . . . . . . . . Material/Diameter/Thickness Table . . . . . . . . . . . . . . . . Flexible Hoses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reusable Hose Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . Installation Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . Airbus A340 Main Landing Gear Lock Springs . . . . . . Common Anti-Friction Bearing Types . . . . . . . . . . . . . . Bearing Defects 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bearing Defects 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bearing Installation Tooling . . . . . . . . . . . . . . . . . . . . . . . Bearing Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standard Chain Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . Chain Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Chain Assembly Arrangements . . . . . . . . . . . . . Non-Reversible Chain Assemblies . . . . . . . . . . . . . . . . . Location of THS Drive Belts . . . . . . . . . . . . . . . . . . . . . . B737 Stabilizer Ball Nut and Jackscrew Inspection . . Types of Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uneven gear wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Build-Up of Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tying cable ends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cable Inspection (A320) . . . . . . . . . . . . . . . . . . . . . . . . . Pulley Inspection (AMM A320) . . . . . . . . . . . . . . . . . . . . Hand-Operated Rolling Tool . . . . . . . . . . . . . . . . . . . . . . Inserting Cable in Terminal . . . . . . . . . . . . . . . . . . . . . . . Go No-go gauging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pull Tester AT520CT . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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477 479 481 483 485 487 489 491 492 495 497 499 501 505 509 511 514 516 518 522 524 526 528 532 534 536 537 541 543 545 547 549 551 553 555
Aug 2004
Cable Tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557 Locking turnbuckles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559 Typical Remote Control System . . . . . . . . . . . . . . . . . . . 561 Types of Teleflex Cable and Typical Sliding End Fittings . . . . . . . 563 Teleflex System Components . . . . . . . . . . . . . . . . . . . . . 565 Teleflex Distributor Box and Torsion Drive . . . . . . . . . . 567 Teleflex Conduit Connectors . . . . . . . . . . . . . . . . . . . . . . 569 Assembly of Teleflex Sliding End Fitting . . . . . . . . . . . . 571 Bowden Control Components 1 . . . . . . . . . . . . . . . . . . . 573 Bowden Control Components 2 . . . . . . . . . . . . . . . . . . . 575 ............................................... 584 ............................................... 587 Examples of Protection Devices on Fuselage . . . . . . . 593 Parking Intervals (Not More Than 2 Days) . . . . . . . . . . 595 Protection Devices on Engine . . . . . . . . . . . . . . . . . . . . . 597 Parking Intervals (not more than 12 weeks) . . . . . . . . . 599 Aircraft Storage - Inspection Intervals . . . . . . . . . . . . . . 601 A/C Storage - Inspection Intervals . . . . . . . . . . . . . . . . . 603 Typical Fuelling/Defuelling Safety Zone . . . . . . . . . . . . 611 DC and 3 Phase Connectors . . . . . . . . . . . . . . . . . . . . . 623 Defect Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628 Visual Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630 Endoscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 Typical Light Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634 Types of Structural Damage 1 . . . . . . . . . . . . . . . . . . . . 637 Types of Structural Damage 2 . . . . . . . . . . . . . . . . . . . . 639 Corrosion Removal Tools . . . . . . . . . . . . . . . . . . . . . . . . . 643 Abrasive Bead-Blasting . . . . . . . . . . . . . . . . . . . . . . . . . . 645 Different Paint Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 658 Paint Build-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660 Influence of Humidity by Application of Primer I . . . . . 662 Influence of Humidity by Application of Primer II . . . . . 664 Epoxy-Primer Application . . . . . . . . . . . . . . . . . . . . . . . . 666 Top Coat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668
CWM LRTT CoM
Figure 281 Figure 282 Figure 283 Figure 284 Figure 285 Figure 286 Figure 290 Figure 292 Figure 295 Figure 296 Figure 297 Figure 298 Figure 299 Figure 300 Figure 301 Figure 306 Figure 307 Figure 308 Figure 309 Figure 310 Figure 311 Figure 312 Figure 313 Figure 314 Figure 315 Figure 316 Figure 317 Figure 318 Figure 319 Figure 320
Figure 277 Figure 278 Figure 279 Figure 280
TABLE OF FIGURES
M7 MAINTENANCE PRACTICES
Figure 321 Figure 322 Figure 323 Figure 324 Figure 325 Figure 330 Figure 331
Electrostatic Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Lightning Strike Areas . . . . . . . . . . . . . . . . . . . . Radiation Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hard Nose Gear Contact . . . . . . . . . . . . . . . . . . . . . . . . . Example of Designed-In Safety Factors . . . . . . . . . . . . Sample: Release-To-Service Certificate . . . . . . . . . . . . Time to Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lufthansa Resource Technical Training
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