Aircraft Systems Lab Manual

AIRCRAFT JACKING PROCEDURE THEORY: For maintenance activities such as rigging, levelling, retraction test, wheel brake assembly change and major component change the aircraft must be jacked up properly. The jacking up can be done by using single point lifting by bottle jack or three point lifting by tripod jack. The jacks may be hydraulic or screw type as supplied by the manufacturer apart from this required the additional tail jacks or trestles may be used in accordance with the maintenance manual or the type of activities. PREFERENCE: It is always recommended to refer the respective aircraft maintenance manual before attempting to perform jacking up operation. AIM: To lift the aircraft by using jacks. REQUIREMENT: Man hours -3 Man power-3+1 Document-aircraft maintenance manual .Equipment-bottle jack, wheel chocks, aircraft ladder PRECAUTIONS:  Refer aircraft manual before jacking up the aircraft to know the correct method /procedure, sequence of operation and requirement of equipment.  Ensure the lifting capacity of the jack and the jacks are fully serviceable.  If necessary fit the jack pads on the aircraft structure.  Avoid aircraft jacking up operation in open area.  Find out the weather status from the ATC/MET department.  Select the hard and level ground.  If required keep trestles ready for use. Do not jack up the aircraft before ensuring that the C.G and gross weight are within safety limits.  Do not attempt to jack up the aircraft by the main gear shock strut.  Ensure that the nose landing gear upper and lower torque links are connected prior to jacking.  Maintain the communication between the crews.  Ensure all ground support units are clear of the aircraft.  Place caution boards/sign boards on the ground near the nose, wing tip and tail of the aircraft.  Keep the safety lines around the aircraft. PROCEDURE:  The procedure of as per type of the aircraft and a per manufacturer instruction.

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Ensure the ground is hard and without slipping. Remove the chokes from the wheels Place the trestles wherever it is applicable. Place all the jacks at specified jacking points. Deploy one person at each jacking joints. Ensure that the jacks are properly placed. Raise the jacks slowly till the contact of the aircraft jacking point is at contact place slightly way out of jack and align it. First raise the nose slightly then simultaneously all the jacks till the wheel or gear from 1 inch from the ground. Engage the lock mechanism and lock the jack to prevent sudden collapse due to hydraulic leakage of jack. If the aircraft is slightly to be jacked more than 24 hours or overnight, it is recommended to adjust the trestles at all specified station to support the aircraft weight. Place a display board (aircraft on jacks) in front of the aircraft. While lowering the aircraft from the jack ensure the parking brakes are in OFF position. No loose items should be available in and around the aircraft while lowering the aircraft and obstruction if any to be clear before lowering.

RESULT: Thus the aircraft is jacked up safely without any damage to men, material and equipment.

AIRCRAFT LEVELING PROCEDURE AIM: To place the aircraft level with the ground by using strain gauge and spirit level method (aircraft type light weight). THEORY: Levelling of an aircraft is the procedure of placing an aircraft in its rigging position by means of lifting the aircraft by hydraulic jacks so as to enable the rigging check on newly assembled aircraft or replacement/renewal of any major component of the aircraft in order to ensure the correct fitting and alignment of aircraft. The rigging position is the position of the aircraft at which longitudinal and lateral axis are parallel to the ground (Straight level position).It can be done by three different methods on the aircraft type as follows. 1. Straight gauge and spirit level (Light aircraft) 2. Plumb bob method (large wide body) 3. Engineers steeper method for supersonic aircraft. NOTE: As the procedure differs always. Therefore always refer the instruction specified by manufacturer for the correct procedure of rigging and instructions required. OCCASIONS: 1. on replacement/renewal of major components. 2. during rigging check. 3. during symmetry check. 4. As required by manufacturers and competent authority. REQUIREMENT: 1. Man hours-3 2. Man power-3+1 3. Document- aircraft maintenance manual, aircraft forms, aircraft rigging charts. 4. Equipment-Tripod jack (hydraulic/screw), aircraft ladder, leveling board, spirit level, tail trestles.

PRECAUTIONS:  Observe all the precautions while jacking up the aircraft.  Check accuracy of spirit level.

PROCEDURE:  Ensure that the aircraft is jacked up properly and place the trestles wherever it is required.  Place the longitudinal leveling board at port side.  Place the spirit level over the longitudinal board.  Adjust the tail trestle till the bubble of the spirit level brought in center.  Repeat the same operation.  Place the spirit level after checking the accuracy.  Adjust the main jacks till the double of the spirit level in brought to the centre.  Recheck the lateral level as well as longitudinal level. CAUTION: Always finish the levelling procedure by checking the longitudinal level without any adjustments.

RESULT: The aircraft is level and ready for further checks.

AIRCRAFT SYMMETRY CHECK PROCEDURE AIM: From time to time it is necessary and advisable to check the alignment of fully assembled aircraft. TOOLS REQUIRED: Aircraft jacks ,pliers ,spirit level/plumb bob ,measuring tape ,drawing of the aircraft ,marker pens, aircraft maintenance manual, aircraft servicing ladder. SAFETY PRECAUTIONS: All precautions as that of jacking and levelling of an aircraft. Do not step on control surface or composite part while taking measurement. GENERAL INFORMATION: Symmetry checks will normally be made after any major structural repair or after the aircraft has been subjected to severe condition such as heavy loading extremes turbines, violent manoeuvres.  Symmetry should also be done if any of the following conditions are observed.  Wrinkled or buckled skin  Area of loose or sheared rivets  Area of badly fitting panels or inspection plates If a pilot process the flight characteristics that cannot be corrected by remission of control, it is that fuselage and wings are out of alignment. PROCEDURE:  Level the aircraft.  Fix the reference point along the axis of the symmetry.  Measure the distance from the reference points on the adjustable component role down the value of drawing.  If all measurements at which the tolerance give the maintanence manual, the aircraft is in correct alignment.  If any of the measurement or not with tolerance, the alignment must be adjusted as specified in maintenance.  Check the vertical symmetry of the aircraft in a like manner by the use of measuring type of check the distance between a tip of the vertical stabilizer and the horizontal stabilizer. DOCUMENTATION:    RESULT:

Enter the maintenance activity carried out aircraft servicing form. Enter the measurement valid on the drawing of the aircraft. Enter the adjustment carried out if any of aircraft servicing form.

Aircraft symmetry check procedure is practiced with an understanding of safety precautions. CONTROL SYSTEMS RIGGING PROCEDURE AIM: To understand the underlying principle of operating procedure for aircraft control system rigging as the method of checking the relative alignment and adjustment of an aircraft main structural component. GENERAL: Aircraft structure must be rigged for alignment of all fixed component where major component are aligned with each other. Alignment of control surfaces and control that move the surface (i.e. adjustment of cable, length, cable tension).Angular deflection of control surfaces must be measured. GUIDING PRINCIPLE: Control surface should move a certain in either direction from the neutral position. These movement of the cockpit control. The flight with the movement of the cockpit control. The flight control system must be adjusted to obtain the requirement. TOOLS REQUIRED: Tensiometer, cable rigging tension chart, protractor, rigging fixtures, contour templates, rulers, hydraulic tools, sow spirit levels. SAFETY PRECAUTIONS: No damage should occur to control surface during control rigging. PROCEDURE:  Positioning of flight control surface system in neutral and temporarily locking it with rig pins or blocks.  Adjusting surface travel, system cable tension, linkages and adjustable stops to the aircraft manufacturer specification.  Keep the flight control system in neutral positioning the external control surfaces lock(i.e.) the form of channel wooden blocks) in place by sliding these into opening between the ends of the cable movable surface and to aircraft structures. SURFACE TRAVEL MEASUREMENTS:  The tool for measuring surface travel primarily include protractors, rigging fixtures, containers, templates and rulers.  Various types of protractors are used for determining the flight control surfaces one protractors that can be measured ailerons, elevators or wing flaps travels in a propeller protractors.  This protractor is made up of frame disk, a ring and two spirit levels.

CONTROL RIGGING PROCEDURE:  Lock the cockpit control bell crank and the control surface in the neutral position.  Adjust the cable position, maintaining the rudder elevator or ailerons in the neutral position.  Adjust the controls stops to limit the control surface travel to the dimensions given for aircraft being rigged check the range of movement of the control and the control surface in both direction from neutral.  Pins, usually called rig pins are something used to simply the setting or pulling, levels in their neutral position. DOCUMENTATIONS: Enter the maintenance operation done in the aircraft servicing team.

RESULT: Thus the control rigging procedure is performed using safety precautions.

FLOW TEST TO ASSESS FILTER ELEMENT CLOGGING AIM: Whenever it is suspected that the hydraulic system has become contaminated (or) the system has been operated at temperature in excess of the specified maximum, check of the system should be made. The Filter in most hydraulic system are designed to remove most foreign particles that are visible to the naked eye, therefore clogging test on filter element would indicate health of the hydraulic system free from suspended particles and absence of excessive wear and tear. Those will also reveal if the system is free from contamination. TOOLS REQUIRED:      

Hydraulic pump to build up working pressure Hydraulic flow meter Hydraulic pressure gauge Fire extinguisher Stop watch Ultrasonic filter.

SAFETY PRECAUTIONS: Since hydraulic fluid is highly inflammable adequate and relevant fire extinguisher should be available. PROCEDURE:    

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Run the motor pump and build up the pressure. Measure the amount of fluid flow per minute with the help of stop watch. Read the pressure differential across the filter from the pressure gauge. Check the recorded figure of the flow rate and the pressure differential between the outlet and inlet of the filter against the value given in the maintenance manual. If the rate of flow is more than that given in the maintenance manual, stop the test and remove the filter and put it through ultrasonic cleaning machine if it is a metallic filter or else replace the filter. If the metallic particles are detected on filter establish the root cause. If the pressure differential across the filter is beyond the limits given in the maintenance manual i. A low differential will indicate filter rupture. ii. A higher differential would indicate clogging. Take corrective actions as outlined above.

DOCUMENTATION: Make relevant entries in aircraft service as the maintenance intervention.

RESULT: Thus the flow test to the air filter element clogging practiced with an understanding of mandatory safety precautions.

PRESSURE TEST TO ASSESS HYDRAULIC EXTERNAL & INTERNAL LEAKAGE AIM: To assess the internal and external leakage in a high pressure hydraulic system since such a leakage would lead to catastrophic consequences in flight if not checked on ground TOOLS REQUIRED:         

Test equipment to generate hydraulic pressure Pressure gauge Flow heater Stopwatch Magnifying lens Inspection lamp Die penetrated test kit for leakage test Maintenance manual Fire extinguisher

SAFETY PRECAUTION: Since hydraulic fluid operations at very high pressure level is very hot and highly inflammable, adequate and appropriate firefighting equipment should be available ready on hand EXTERNAL LEAKAGE TEST: External leakage would occur on joints due to inadequate lightness, inefficiency of rubber gasket, seals (or) due to cracks in hoses or pipelines PROCEDURE:  Generate pressure in the system to normally operating level  Carefully examine whether the flow is flowing smooth or with fluctuation indicting leakage  Similarly check-up the reading on the pressure gauge for fluctuation. Fluctuation indicates leakage.  Check the level of hydraulic reservoir. If the level drops constantly, it also indicates external leakage.  Systematically check all joints, starting from the reservoir on all pressure pipes and return pipe up to reservoir.  If there is a leakage detected by tightening a joint; if it holds rubber gasket or seal, switch the pump change the gasket with a serviceable (or) tighten the joints, run the pump and check the leakage.  If crack in a pipeline is suspected apply a dye-penetrant in pipe length and carry. INTERNAL LEAKAGE TEST: Internal leakage could occur due to internal malfunction of hydraulic components such as hydraulic boosters, hydraulic actuators, accumulators etc.

PROCEDURE: Run the hydraulic pump and build a pressure in the system. Start the stopwatch and switch off the pump Constantly monitor the readings of the hydraulic pressure gauge Do not operate any controls Stop the stop watch when pressure drops to the level specified in the maintenance manual e.g. from 280 bar – 150 bar; 280 bar – 100 bar.  Record these timings and check against the allowable time levels in the maintenance manual. If the time taken for the drop is less than that specified, it indicates internal leakages level higher than the acceptable level due to wear and tear.  Individual components contribution to higher internal leakage rates tend to be identified and replaced as per maintenance manual.     

RESULT: Thus the pressure test to assess hydraulic internal and external leakages is done using the mandatory procedures.

FUNCTIONAL TEST TO ADJUST OPERATING PRESSURE AIM: Pump output pressure to determine the smoothness and efficiency of operation of service operator by the hydraulic system. Its pressure output is controlled by a combination of pressure relief valve, pressure regulator and pressure gauge. The aim is to understand the procedure to adjust the operating pressure of the hydraulic system. TOOLS REQUIRED:     

Hydraulic pressure generation kit Combination of pressure relief valves Pressure regulator Pressure gauge Fire extinguisher

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Make sure that all safety precautions are ready Run the pump at minimum rpm, read the pressure gauge. Build-up the pump rpm until it reads fuel pressure. Note down the pressure on the pressure gauge Adjust the pressure using the pressure regulator. Check for any leakage in the hydraulic tubes If yes, replace the hydraulic tubes Check for proper retraction of landing gear.

RESULT: Thus the functional test to adjust operating pressure is performed with necessary safety precautions.

PRESSURE TEST PROCEDURE ON FUEL SYSTEM COMPONENTS AIM: Aircraft fuel system depends on pressurization of its fuel tanks to differential level to achieve the sequence of consumption, ensures movement of CG and hence longitudinal stability within the design value. This experiment would allow an understanding of various components active in the fuel system pressurization and consumption process. TOOLS REQUIRED:           

Fuel system set-up Pressure gauge Fuel system Pressurization unit Compressed air cylinder with regulator and safety valves. Electrical power supply. 28 V DC Fuel flow meter Fuel level indicator Failure warning panel Fire extinguisher

SAFETY PRECAUTIONS:  Fuel is highly combustible hence no flame in the vicinity.  Suitable fire extinguisher and fire safety precautions. PROCEDURE:  Connect the fire compressed air cylinder to the pressurization unit.  Open the air flow slowly  Observe the pressure values at different tanks or measure from the individual pressure gauges connected to various tanks  Run the booster pump; observe the sequence fuel flow as per level of pressurization in tanks.  Cut off pressurization air to one tank and observe “tank feeding” light coming on its failure warning panel of fuel.  Note down the pressurization level of different tanks  Stop the test DOCUMENTATION: Record the maintenance operations carried out on an aircraft servicing form.

RESULT:

Thus the pressure test on fuel system components is done using mandatory procedures.

BRAKE TORQUE LOAD TEST ON WHEEL BRAKE UNITS AIM: To study the brake torque load test on wheel brake units. OCCASION: When an aircraft brakes are damaged, the brake torque load test on wheel brake units is required. PROCEDURE:  Brake torque load test is normally a simple test driven model, brake torque is a function of brake pressure and aircraft velocity as wheel speed.  Basically aircraft tyres are designed for intermittent usage at much higher loads than automobile tyres.  Brake torque load test equipment basically consists of i. Electric power motor ii. Wheel iii. Fulcrum support iv. Brake pedal v. Open belt assembly vi. Rpm indicators vii. Loads  With this components we can measure torque of aircraft wheels on various load condition.

Where, Vx = angular velocity Wx= angular velocity R = Rolling radius  Assuming the operating conditions for the equipment are constant, a brake having a retarding torque equal to the full load torque of the motor to which it is applied is usually satisfactory.  The torque can be determined by the brake units,

Where, T = Brake Torque

HP= Horse Power 5250 = Constant SF = application service factor  Wheel brake procedure function at the wheel is to slow (or) stop the rotation of the wheel light aircraft use a single disc type brake but large transport aircraft require multiple disc to deal with forces generated.

RESULT: Thus the brake torque load test on brake units is studied.

MAINTENANCE & RECTIFICATION OF SNAGS IN HYDRAULIC & FUEL SYSTEM AIM: To understand the essentials of maintenance and up-keep of hydraulic and fuel system components. To understand the logical sequence of troubleshooting with reference to rectification of hydraulic and fuel system. TOOLS REQUIRED: HYDRAULIC SYSTEM: Hydraulic pressure gauge to read up to 300 bar pressure, common tool bar, hydraulic system diagram up to component level, multipurpose patch test kit, clean glass bottle of some capacity and waste cloth. FUEL SYSTEM: Pressure gauge to read up to 5 bar pressure , common tool bar, fuel system diagram up to component level, water detecting capsules, clear glass jar of 5 litre capacity, waste cloth and drip tray. SAFETY PRECAUTIONS:  Since hydraulic fluid and fuel are both highly combustible all fire precaution availability of fire extinguisher for liquid fire are mandatory.  Waste cloth and drip tray must be available readily to avoid spillage of hydraulic oil (or) fuel on the ground.  Avoid to prevent jamming and cracking. MAINTENANCE PROCEDURE:  Systematically start from one end of the aircraft and reach ground in a clockwise direction till for you reach the same.  For convenience, the whole aircraft is divided into 8 parts. Checks are carried out in system components including pipelines.  Level of air reservoir (or) fuel in tanks as seen from built in indicator.  Free movement of control surfaces.  Check for undercarriage bay and aircraft components.  Serviceability of cockpit indicator and failure warning panel. RECTIFICATION OF SNAGS: HYDRAULIC SYSTEMS:     

They may be broadly divided into four parts. Those related to pressure generations and distribution system. Those related to component malfunctioning. Leakage Indication system electrical failure.

SNAGS RELATED TO PRESSURE GENERATION AND DISTRIBUTION SYSTEM: Pumps Not Building Pressure:  Ensure level in the reservoir in between the minimum and maximum level marked.  Run the pump on the aircraft on their stand and measure pressure output.  Adjust pressure regulator if necessary.  Ensure no abnormal pressure rise when pump runs.  Check drive shaft conditions.  Check operations of safety valve at correct pressure.  Ensure system isolation solenoid valve is not closed.  If all else fails, replace the pump. SNAGS RELATED TO COMPONENT MALFUNCTIONING: Malfunctioning of Servo Actuators:  Check the pressure input to the servo actuators.  Check the availability of electrical power to the servo control unit of the servo actuators.  Check for quality of hydraulic fluid, free from impurities which could block the servo control mechanism.  Check the free movement of servo actuator jacks.  If any of the above failures, replace the servo actuators. RECTIFICATION OF LEAKAGES:  Check if the leak is from the joint of two pipelines, if yes open and ensure presence of serviceable gasket seal at joint.  If the check is from the body of the pipeline, check for cracks.  If the leakage is from the body of the component replace the component. RECTIFICATION OF INDICATION SYSTEMS ELECTRICAL FAILURE: If the check indicates proper functioning of component build-up and the leakage indicator in cockpit show malfunctioning then  Check the electrical input of the cockpit.  Check the serviceability of in final warning panel.  Check output from pressure transmitter if all else is ok replace hydraulic pressure indicator. FUEL SYSTEM: Here again snags may be classified into    

Those related to failure of feed from tank. Those related to malfunctioning of components. Leakages Indication supplier electrical failure.

SNAGS RELATED TO FAILURE OF FEED FROM TANK: Feed failure could be due to,

 Lack of pressurization in the tank.  Check fuel level and top it when low.  If input to unit shows zero pressure, trace the line backward up to the reduced level and correct the fault.  If the input is OK and the output is faulty replace the pressurization unit. DOCUMENTATION: Enter the maintenance work and rectification work carried out in the appropriate columns of the aircraft servicing form.

RESULT: Maintenance and rectification of snags in the hydraulic and fuel system studied in depth to develop diagnostic skill based on full understanding of the aircraft systems.