APU
-CROSSOVER DUCT THERMAL SWITCH (2 EACH)

-WING LEADING EDGE DUCT THERMAL SWITCH (2 EACH)
Duct Leak Detection System Component Location Figure 1 (Sheet 3)
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A 747-400 MAINTENANCE MANUAL
WIRING

THERMAL
SWITCH

THERMAL SWITCH
(EXAMPLE)

THERMAL SWITCH
(EXAMPLE)

Duct Leak Detection System Component Locations
Figure 1 (Sheet 4)

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A
747-400
MAINTENANCE MANUAL

E2-6
Wing Leading Edge Duct Leaks Detection System Simplified Schematic Figure 2
A42776
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A
747-400
MAINTENANCE MANUAL

 C.  When the ground test is initiated, the CMC outputs five simultaneous test initiating signals which activate five test relays. These test relays send various discrete signals to the fire detection card file. From these inputs, the fire detection card file generates fire, overheat, and fault detection discretes which it sends to the EIUs and MAWEA. The MAWEA sends signals received from the fire detection card file to the CMC on an ARINC 429 bus, and the MAWEA also sends signals received from the fire detecteion card file to the EIUs or two ARINC 429 buses. While the test is in progress, the CMC monitors all fire detection system interfaces to the EIUs and the MAWEA. If the CMC detects an inoperative interface, it displays an appropriate fault message.
 D.  The test relays can also be activated by pressing FIRE/OVHT test switch on the M7317 (P5) miscellaneous switching panel, but the test initiated by the CMC is more effective at isolating failures. The FIRE/OVHT test switch on M7317 tests critical wiring paths, while the CMC tests all wiring paths and isolates to the failed interface with a text message.
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A
747-400 FAULT ISOLATION/MAINT MANUAL
DUCT LEAK DETECTION SYSTEM
COMPONENT  FIG. 102 SHT  QTY  ACCESS/AREA  REFERENCE 
CARD - AFOLTS ENG 1 TURB OVHT, YLPA5  1  1  LEFT OF NOSE GEAR WHEEL WELL, FIRE DETECTION CARD FILE, M826  26-10-01 
CARD - AFOLTS ENG 2 TURB OVHT, YLPA10 1  1  LEFT OF NOSE GEAR WHEEL WELL, FIRE DETECTION CARD FILE, M826 26-10-01 
CIRCUIT BREAKERS - 1  FLT COMPT, P6 
ALT PWR APU LOOP A  1  6C5  * 
FIRE/OVHT TEST 5, R8052 LEFT DUCT LEAK INDICATION, R7420 RIGHT DUCT LEAK INDICATION, R7419 RELAY - (REF 31-01-36, FIG. 101) ENG FIRE/OVHT DET APU LOOP A, C8807 MODULE - (REF 26-11-00, FIG. 101) MISCELLANEOUS SWITCHING, M7317  1  6H14  * 
SWITCH - FIRE/OVHT TEST (S1)  1 1  SWITCHING MODULE, M7317 FLT COMPT, P5, MISCELLANEOUS  * 
SWITCH - THERMAL, S873  2  1  600, RIGHT WING  26-18-02 
SWITCH - THERMAL, S874  2  1  600, RIGHT WING  26-18-02 
SWITCH - THERMAL, S875  2  1  600, RIGHT WING  26-18-02 
SWITCH - THERMAL, S876  2  1  600, RIGHT WING  26-18-02 
　
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