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A
747-400
MAINTENANCE MANUAL
P415 POWER DISTRIBUTION CENTER-RIGHT
APU FIRE SHUTDOWN MODULE
APU Fire Detection System Simplified Schematic Figure 3
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4.
5.
6.
7.
A
747-400 MAINTENANCE MANUAL
B. The detection control cards are in the M826 fire detection card file. The card is in the electrical/electronic equipment compartment, along the left side of the nose gear wheelwell.
C. The Loop A and Loop B fire detection control cards operate in "OR" logic. A fire condition sensed on any one fire detection control card (Loop A or Loop B) will result in an alarm.
Automatic Fire Overheat Logic Test System Cards (AFOLTS)
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A. An AFOLTS card interprets detection control card signals, provides system functional tests, and outputs fire/overheat warning and fault indication signals for APU fire detection system. There are total of seven AFOLTS cards in fire detection card file.
B. The AFOLTS card is located in the M826 card file.APU Fire Shutdown Module (M869)
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A. An APU fire shutdown module is mounted in the right main wheel well. The panel allows ground personnel to be alerted to a fire condition in the APU, since the APU is used primarily on the ground. This panel has a red fire light, a fire warning horn, remote APU stop switch, and a switch to discharge the APU fire extinguisher.
B. A relay in the landing gear area disables the wheel well horn circuit when the landing gear is not extended. The wheel well horn is disabled when the APU fire switch on fire control module (M7326) is pulled, or the APU FIRE CONTROL switch on APU fire shutdown module (M869) is pulled down. Pulling down the APU FIRE CONTROL switch on M869 shuts down the APU and provide a continuous circuit to APU fire extinguisher bottle squib. This also enables the FIRE EXTINGUISHER DISHCARGE switch on M869.
Fire Control Module
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A. The fire control module M7326 is located on P5 pilot's overhead panel. This module contains engine fire, APU fire, lower cargo fire detection and extinguishing system (Ref 26-21-00).
B. In case of fire in the APU, the following features appear:
(1)
APU switch handle: Illuminates. Rotating the switch discharges the extinguishing agents.
(2)
APU bottle discharge light: Illuminates after the extinguishing agents are discharged.
C. To replace the module, refer to 26-21-01/401, Fire Control Module.Fire/Overheat Test Module (Fig. 1)
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A. The FIRE/OVHT TEST switch is located on M7317 miscellaneous switching panel (P5). The switch initiates tests for the various fire detection systems. The operational test for each applicable section contains the FIRE/OVHT test. By pressing the switch, the switch sends a signal to a relay that simulates a fire/overheat signal. The test results in cockpit fire and overheat indicators, and appropriate EICAS messages.
B. To replace the module, refer to 26-10-02/401, Miscellaneous Switching Module.
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MAINTENANCE MANUAL
8. Operation (Fig. 2)
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A. Functional Description
(1)
With 28-volts dc on each control card, a voltage is induced upon each loop. Both ends of each loop are tied together electrically at each control card. During test, the two ends are separated and on one end, a fault and fire simulation are placed on each loop. This tests continuity of the loop and detector card circuitry.
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