Aoa 737ngx Groundwork Fire Protection English Transcript
April 6, 2017 | Author: lcesardias | Category: N/A
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Transcript for Groundwork Fire Protection...
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Nick Collett | 2011
PMDG 737NGX GroundWork – FIRE PROTECTION
Fire Protection Lesson Introduction This lesson will cover the following f ollowing topics: o A brief overview of the fire protection systems on the 737NG, o Engine overheat detection, o Engine fire detection and extinguishing, o APU fire detection and extinguishing, o Wheel well fire detection, o Engine/APU/wheel well fire protection systems tests. o Cargo compartment smoke detection and fire extinguishing, o The cargo compartment fire protection system test, o Lesson summary.
Fire Protection Overview The 737NG has fire detection and extinguishing systems for the: o Engines, o APU, o Cargo compartments o Lavatories. The main gear wheel well also has a fire detection system, but no fire extinguishing capability. As well as fire detection and extinguishing systems, the engines also have overheat detection capability. The various fire detection and extinguishing systems have a clear purpose – to – to combat one of the most dangerous threats to safety in the air – air – fire. fire. We will run through these systems one by one, but first let’s give a brief overview overview of the locations of the controls and indications for the various systems that we’ll be covering in this lesson. o The Master Fire Warning lights are located on the glareshield. o Controls and indications for the engine overheat, fire detection and extinguishing systems are located on the overheat/fire protection panel. o The APU fire detection and extinguishing system controls and indications are also located here, as well as the Wheel Well Fire Warning light. o The Cargo Fire Panel, also located on the aft electronic panel, houses controls and indications for the cargo fire detection and extinguishing system. The lavatories have smoke detection and fire extinguishing systems installed. o The lavatory fire extinguishers trigger automatically when a fire is detected, and the
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o
flight deck has no indication of extinguisher discharge. Some 737s have a LAVATORY SMOKE light on the forward overhead panel. This is a customer option, and ours does not.
Engine Overheat and Fire Detection/Extinguishing Systems Engine Overheat Detection Each engine has two overheat/fire detector loops. Each engine has eight overheat/fire detectors located in pairs monitoring four different sections of the engine: o Upper fan case, o Lower fan case, o Left core section, o Right core section. Each pair of detectors consists of one detector from loop A, and one detector from loop B. o Each of these loops provides both fire and overheat detection. o There are predetermined temperature thresholds for engine OVERHEAT and engine FIRE conditions. o When the temperature of a detector reaches the OVERHEAT threshold, it will signal an OVERHEAT condition. o If the temperature increases further to the FIRE threshold, the detector will signal a FIRE condition. Each detector has a sealed stainless steel sense tube fi lled with inert gas. o As the temperature around the tube increases, the gas expands. o Expansion of the gas increases the pressure in the tube, which is sensed by three pressure switches. o Each of the pressure switches trips at different pressure thresholds. The FAULT pressure switch is normally held closed by gas pressure in the tube. If a leak occurs and pressure drops, the switch opens triggering a FAULT condition. The OVHT and FIRE pressure switches are calibrated to trip closed at pressures which correspond to the temperature thresholds we mentioned earlier. o If temperatures reduce again and the gas pressure in the tube reduces to normal, the OVHT and FIRE switches will open again and the overheat or fire conditions will be reset. The two separate detector loops in each engine are installed for redundancy. It is possible to manually select either of the two loops in each engine to be the active detecting loop. o This is achieved using the two OVHT DET switches on the Overheat/Fire Protection Panel.
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There are two switches, one for each engine. o Each switch has three positions: The A and B positions select loops A or B individually to be the sole detecting loop for that engine. With the switch in the NORMAL position, BOTH loops must sense an overheat or fire condition before a warning is activated. The NORMAL position also provides redundancy – if the NORMAL position is selected and one loop fails, it is automatically deselected and the remaining loop remains active as the single detector loop. For this reason, standard procedure is to use the NORMAL position. o A detector loop failure may be indicated by the illumination of the FAULT light on the Overheat/Fire Protection Panel. Whether or not the fault is actually indicated however depends on the position of the OVHT DET switches. If the switches are in the NORMAL position and one of the loops on either engine fails, there will be NO indication of the failure. If a failed loop is manually selected using either of the OVHT DET switches, the FAULT light will ill uminate indicating failure of that loop. If the switch is in NORMAL and BOTH loops for an engine fail, the fault light will illuminate. To summarize - the FAULT light will only illuminate if a failed loop has been manually selected using one of the OVHT DET switches, OR if BOTH loops have failed. If an overheat condition is detected on the selected loop, or on BOTH loops if the OVHT DET switch is in the NORMAL position, the corresponding ENG OVERHEAT light will illuminate. o There are two ENG OVERHEAT lights, one for each engine. In the event of an overheat condition in either engine, the following will occur: o The corresponding ENG OVERHEAT light illuminates. o Both MASTER CAUTION lights illuminate, o The OVHT/DET system annunciator light illuminates. o
Engine Fire Detection We’ve already covered the two detector loops present in each engine. o When the detectors sense a temperature higher than the overheat threshold, they trigger an overheat warning. o If temperatures continue to rise above a further threshold, a fire warning is triggered. o Bear in mind that these are the same detector loops covered earlier when talking about the engine overheat detection. Everything we said about the OVHT DET switches and the FAULT light still stands. In the event of a fire condition in either engine, the following will occur:
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o o o o
The fire warning bell sounds, Both master FIRE WARN lights on the glareshield illuminate, The corresponding engine fire switch illuminates, The relevant ENG OVERHEAT light illuminates.
Engine Fire Extinguishing The engine fire extinguishing system has two fire bottles, located together in the aft left corner of the main gear wheel well. o Each individual bottle is capable of discharging into either of the two engines. o Each bottle contains Halon 1301 gas that is discharged through three ports in the engine. o Once discharged, the Halon dissipates quickly, so bear in mind that this is NOT a fire suppression system. It is purely for extinguishing an existing fire. o There are two squibs per fire bottle. The squibs are small, electrically actuated explosive devices that break the diaphragm seals on the bottle. The Halon gas is then expelled from the bottle by pressurized nitrogen at an initial discharge pressure of 800psi. The #1 squib on each bottle directs halon t o engine 1. The #2 squib on each bottle directs halon to engine 2. o It is therefore the squibs which determine which engine the bottle discharges to. There are two red engine fire switches on the Overheat/Fire Protection Panel. These are used to discharge the fire bottles. Before the bottles can be discharged however, the handle must be pulled up. o There is a locking mechanism that prevents the handle from being pulled up inadvertently. o The locking mechanism is automatically released when an overheat or fire condition is detected. o It is possible to override it manually by pushing the switch beneath the handle. Pulling out an engine fire handle does the following for the corresponding engine: o Trips off the engine Generator, o Disables thrust Reverser, o Arms the squib on each fire bottle corresponding to that engine, o Closes the engine Bleed valve (PRSOV), o Deactivates the related EDP LOW PRESSURE light, o Closes Fuel and Hydraulic valves. o Acronym: GRAB Da Fire Handle. o Pulling out the fire handle allows it to then be rotated either clockwise or anticlockwise. The direction of rotation of the handle determines which bottle is discharged into that engine. o Turning the handle to the left will discharge the left bottle into the engine.
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Turning the handle to the right will discharge the right bottle into the engine. o This is the case for both of the engine fire handles. o When a bottle is discharged, the bottle pressure reduces. When pressure drops below 250 psi, the corresponding BOTTLE DISCHARGE light illuminates. o The engine fire switch will remain illuminated red until the detector temperature has dropped below the fire condition threshold. It’s worth noting that the extinguishers are powered by the hot battery bus, meaning that they can be activated regardless of the position of the BAT switch on the forward overhead panel. The detection systems are powered by the battery bus however, so the BAT switch must be selected ON for the detection systems to function. o
APU Fire Detection/Extinguishing Systems APU Fire Detection The APU does not announce an overheat condition in the same way as the engines do. This is a fire detection system only. APU overtemperature will trigger a protective shutdown and the FAULT light on the Forward Overhead Panel. APU fire detection is provided by a single detection loop. The APU fire detection loop has three detectors: o Upper APU compartment, o APU compartment door, o Tailpipe. When a detector temperature increases above a predetermined threshold, it senses and announces a fire condition. APU Detector loop failure is indicated by the illumination of the APU DET INOP light on the Overheat/Fire Protection Panel. The APU fire detectors are of a type similar to those used in the engines. o As temperature rises, the pressure of the inert gas in the sense tube increases, tripping a pressure switch which supplies a FIRE signal. o There is also a FAULT pressure switch which opens when pressure drops below normal, triggering a FAULT condition. In the event of a fire condition in the APU, the following will occur: o The fire warning bell sounds, o Both master FIRE WARN lights on the glareshield illuminate, o The APU fire switch illuminates, o The FAULT light on the APU panel illuminates, triggering a master caution and the APU system annunciator light. Additionally, a warning horn in the main gear wheel well sounds, and a collocated warning light flashes. Page 5
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There is actually a means of discharging the APU fire bottle from down there in the wheel well, using the APU Ground Control Panel. The APU is shut down automatically when a fire is detected. Extinguishing the fire still needs to be commanded manually however. o
APU Fire Extinguishing The APU has its own fire bottle, also containing Halon 1301. The APU fire bottle is located in the horizontal stabilizer accessory compartment. It has a single squib that breaks the diaphragm seal on the bottle and discharges the Halon into the APU compartment. There is an APU fire switch on the Overheat/Fire Protection Panel that functions similarly to the two engine fire switches. It is locked down until the APU fire detector loop senses a fire condition. Like the engine fire switches the lock can be overridden by pushing the switch beneath the handle. Pulling out the APU fire handle does the following: o Trips off the APU Generator, o Arms the APU fire bottle squib, o Closes the APU Bleed valve, o Closes the APU Fuel shutoff valve, o Closes the APU air Inlet door. o Acronym: GABFI. o Like the engine fire handles, the APU fire handle can then be rotated to discharge the bottle. The APU fire switch can be rotated in either direction, but as there is only one bottle with only one squib, it makes no difference which direction you rotate it. That said, it’s best to rotate the switch to the right so that the annunciator lights are still visible from the first officer’s perspective. When the bottle is discharged and pressure reduces below 250 psi, the APU BOTTLE DISCHARGE light illuminates. The APU fire switch will remain illuminated red until the detector temperature has dropped below the fire condition threshold. Similarly to the engine fire extinguishing system, APU extinguishing is powered by the hot battery bus. o The detection system is powered by the battery bus.
Wheel Well Fire Detection System The main landing gear wheel well has a fire detection system. There is NO fire extinguishing system. The nose landing gear wheel well has neither a fire detection system NOR a fire extinguishing system. Page 6
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There is a single overheat sensing element mounted on the ceiling of the main gear wheel well. o The element is a thermistor type where resistance varies inversely proportional to temperature. o This means that an increase in temperature results in a decrease in resistance. o This reduction in resistance allows a current to pass through the element, triggering a fire alert. o The resistance is low enough to permit passage of current at and above approximately 205 Celsius, so this is the fire warning threshold for the wheel well. In the event of a fire condition in the wheel well, the following will occur: o The fire warning bell sounds, o Both master FIRE WARN lights illuminate, o The WHEEL WELL fire warning light illuminates on the Overheat/Fire Protection Panel. There is no indication of a wheel well detector loop failure. Fire detection for the wheel well is powered by AC Transfer Bus 2.
Engine/APU/Wheel Well Fire Protection Systems Tests FAULT/INOP Test The FAULT/INOP test is initiated by holding the ‘FAULT/INOP and OVHT/FIRE TEST’ switch to the FAULT/INOP position. o This is a spring loaded switch, so it must be held in position to carry out the test. This carries out a test of the of the engine and APU fault detection circuits. Faults are simulated to check the circuits’ ability to detect a fault. A successful test of the detection circuitry should flag up the follow ing indications: o Both MASTER CAUTION lights on the glareshield illuminate, o The OVHT/DET system annunciator light on the glareshield illuminates, o The FAULT and APU DET INOP lights on the Overheat/Fire Detection Panel illuminate. o That gives 5 yellow lights in total for the FAULT/INOP test.
OVHT/FIRE Test The OVHT/FIRE test is initiated by holding the ‘FAULT/INOP and OVHT/FIRE TEST’ switch to the OVHT/FIRE position. o This is a spring loaded switch, so you need to hold it in position to carry out the test. When the switch is released and centered, the test stops and the indications extinguish. The OVHT/FIRE test is a test of the overheat and fire detection loops on the engines, the APU and the wheel well. A successful test of the fire detection loops should fla g up the following indications:
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The fire warning bell sounds, o Both master FIRE WARN lights illuminate, o Both MASTER CAUTION lights illuminate, o The OVHT/DET system annunciator light illuminates, o Both engine fire switches illuminate, o The APU fire switch illuminates, o Both ENG OVERHEAT lights illuminate, o The WHEEL WELL fire warning light illuminates, o That gives 11 lights in total (a combination of red and yellow) and the bell. Additionally to the indications on the flight deck, the OVHT/FIRE test also activates the APU fire warning horn and a flashing light in the wheel well. We mentioned earlier when we were talking about the wheel well fire detection system that it is powered by AC Transfer Bus 2. o In contrary, all of the systems tested by the OVHT/FIRE test are powered either by the Hot Battery Bus or the Battery Bus, so will indicate correctly even without AC Power. o The WHEEL WELL light is the exception, so will not illuminate if AC Transfer Bus 2 is not powered. o
Extinguisher Test The extinguisher test is initiated by holding the EXT TEST switch to the 1 or 2 positions. For a test of the complete system, both positions should be checked. o This switch is spring loaded, so needs to be held in position to confirm the results of the test. We discussed earlier that fire bottle discharge is achieved by the firing of a squib which punctures the diaphragm seal on the bottle and frees the contents. The extinguisher test is a test of the circuit continuity between the engine and APU fire switches and the squibs on the fire bottles. Moving the EXT TEST switch to the 1 position tests the #1 squib on each engine fire bottle, and the squib on the APU fire bottle. Moving the EXT TEST switch to the 2 position tests the #2 squib on each engine fire bottle, and the squib on the APU fire bottle. There is only one APU fire bottle, and that bottle only has one squib, so the switch tests the same squib in both positions. Three green lights indicate healthy squib circuitry.
Mid-Lesson Summary So far in this lesson we’ve covered: o Engine overheat detection, o Engine fire detection, o Engine fire extinguishing, Page 8
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APU fire detection, o APU fire extinguishing, o Wheel well fire detection. Under system tests we covered: o FAULT/INOP test, o OVHT/FIRE test, o Extinguisher test. Later in this lesson we will cover: o Cargo compartment smoke detection, o Cargo compartment fire extinguishing, o Cargo compartment fire protection system test, o Lesson summary. o
Cargo Compartment Smoke Detection/Fire Extinguishing Systems System Overview The 737 has two cargo compartments – forward and aft. Both holds are sealed and pressurized but have no fresh air circulation or temperature control. Some heating is provided by cabin air exhausted around their walls. Cargo compartment smoke detection and fire extinguishing systems are installed for both cargo compartments. o Like the engine and APU fire bottles, the cargo compartment bottles use Halon 1301.
Cargo Compartment Smoke Detection Cargo compartment fire warnings are triggered by smoke detectors in each compartment. o The forward cargo compartment has four smoke detectors – two in loop A and two in loop B. o The aft cargo compartment has six smoke detectors – three in loop A and three in loop B. It is possible to manually select either of the two loops to be the active detector loop in each cargo compartment. o This is achieved using the two DET SELECT switches on the Cargo Fire Panel. o There are two switches; one each for the FWD and AFT cargo compartments respectively. o With either A or B selected, the system acts as a single loop system, and a fire alert will be activated only when a detector from th e selected loop detects smoke. o With the NORM position selected, a detector from loop A and a detector from loop B must detect smoke to trigger an alarm. o The NORM position also provides redundancy – if the NORMAL position is selected
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and one loop loses power, it is automatically deselected and the remaining loop remains active as the single loop. A detector loop failure may be indicated by the illumination of the DETECTOR FAULT light on the Cargo Fire Panel. o Similarly to the engine detector FAULT light, whether or not the light illuminates depends on which loop is selected by the DET SELECT switches. o The DETECTOR FAULT light indicates that at least ONE of the SELECTED loops has failed in either compartment. o If one loop has failed for instance, but the still functioning loop has been selected with the DET SELECT switches, the DETECTOR FAULT light would not illuminate. o With the DET SELECT switches in the NORM position, an illuminated DETECTOR FAULT light indicates that both loops in either cargo compartment have failed. The smoke detectors use photoelectric cells to detect smoke. o They send an alarm signal when smoke is detected or if air temperature rises above 110 Celsius. In the event of a smoke or overheat condition in either cargo compartment, the following will occur: o The fire warning bell sounds, o Both master FIRE WARN lights illuminate on the glareshield, o The FWD and/or AFT cargo fire warning light(s) illuminate on the Cargo Fire Panel. Either of these lights can illuminate individually to indicate a fire in a single specific cargo compartment. A smoke or overheat condition in either of the cargo compartments also triggers the cabin pressure control system to gradually reduce cabin altitude at 750fpm. o This ensures that during a subsequent emergency descent the cabin is always overpressurized to prevent smoke from entering the cabin.
Cargo Compartment Fire Extinguishing The cargo compartments on a standard passenger configuration 737 are classified as Class C. The installed fire suppression system needs to be capable of providing: o A minimum initial 5% Halon concentration throughout the compartment after bottle discharge to suppress any fire to controllable levels, o A minimum 3% Halon concentration throughout the compartment for 60 minutes thereafter to prevent re-ignition or spreading of the fire. Our aircraft is certified to ETOPS-180, so to meet certification requirements a second bottle is installed giving an additional 120 minutes o f protection, for 180 minutes total. The two cargo compartment fire bottles are installed in the air conditioning mix bay on the forward wing spar. Like the engine and APU fire bottles, these contain Halon 1301 which is expelled by pressurized nitrogen through a diaphragm seal punctured by a squib. There are two discharge nozzles in the forward cargo compartment, and three discharge Page 10
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nozzles in the aft cargo compartment. The bottles are discharged one by one, and can be discharged into either cargo compartment. o The first bottle is discharged in its entirety at a high rate to suppress any fire to controllable levels and provide that 3% Halon concentration for 60 minutes. o A timer is then started, and after 60 minutes the second bottle is discharged automatically. o The second bottle is discharged at a metered, reduced flow rate to continue the 3% Halon concentration for a further 120 minutes. o Discharge of the second bottle can be disabled by disarming the system. o If the aircraft lands after the first bottle has been discharged, but the second bottle is still armed for discharge, discharge of the second bottle is inhibited automatically. o Opening the affected cargo compartment’s door after landing will cause the Halon suppressant to disperse, so the fire may erupt again. The door must therefore not be opened until fire crews are ready to combat the fire. There are two Cargo Fire ARM switches on the Cargo Fire Panel which arm the system for discharge into the forward or aft compartments respectively. o These switches are used to select the compartment that the bottles will be discharged into. Once the desired compartment has been selected, the guarded Cargo Fire Bottle DISCH switch is used to discharge the bottles into that compartment per the scheduling we just explained. o Once discharge has occurred, the DISCH light illuminates on the switch. Again, this is triggered by a pressure switch once pressure drops below 250 psi. Cargo compartment smoke and overheat detection is powered by DC Bus 1 and DC Bus 2. Cargo compartment fire extinguishing is powered by the hot battery bus.
Cargo Compartment Fire Protection System Test There is a single TEST button on the Cargo Fire Panel. Pushing this initiates a test of the detector loops and squib circuits. A successful test of the detector loops and squib circuits should flag up the following indications: o The fire warning bell sounds, o Both master FIRE WARN lights illuminate, o The FWD and AFT extinguisher test lights illuminate, o The FWD and AFT cargo fire warning lights il luminate, o The cargo fire bottle DISCH light illuminates, If any of the detectors in the selected detector loops have failed, the DECTECTOR FAULT light will illuminate during the cargo fire test. o The DETECTOR FAULT light should not illuminate during a successful test. Page 11
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The two extinguisher test lights should ill uminate green during the cargo fire test to indicate that the circuits to the bottle squibs are functional.
Lesson Summary A comfortable and comprehensive understanding of the fire protection systems on your aircraft is vital. In the event of a fire of any kind, the onus is on the crew to act decisively and safely Workload increases dramatically, which is when background knowledge easily recallable to mind comes into play. In this lesson, we’ve covered: o A brief overview of the fire protection systems on the 737NG, o Engine overheat detection, o Engine fire detection and extinguishing, o APU fire detection and extinguishing, o Wheel well fire detection, o Engine/APU/wheel well fire protection systems tests. o Cargo compartment smoke detection and fire extinguishing, o The cargo compartment fire protection system test.
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