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MAINTENANCE MANUAL
Wheel Well Fire Detection Component Location
Figure 1 (Sheet 1)
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MAINTENANCE MANUAL
P50 - CARD FILE
F Wheel Well Fire Detection Component Location Figure 1 (Sheet 2)
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(b) The control card contains a microprocessor and memory which performs fault detection and BITE functions. If a fault is detected, a record is made in memory, for recall as required. A cover plate is installed on the card. The cover plate contains a LED display and four BITE pushbutton controls, identified as DISP TEST, LOC TEST, MEM CLR and MEM READ.
C. Fire/Overheat Test Panel
________________________
(1) The fire/overheat test panel is on the pilots' control stand P8. The test panel contains the wheel well test switch and switches and relays associated with other fire and overheat detection systems.
D. Wheel Well Fire Light
_____________________
(1) The WHEEL WELL FIRE light is on the first officer's instrument panel P3. The light provides a red annunciation when on.
3. Operation_________
A. Functional Description (Fig. 2)
(1)
The system receives 115-volt standby ac power from overhead panel P11 circuit breaker WW FIRE DETECTION. The WW FIRE TEST circuit breaker on P11 provides battery bus 28 Vdc power to turn on the FIRE warning lights.
(2)
When a segment of the overheat sensor reaches a temperature of 400 degrees F, an alarm condition (low resistance) is sensed. Whenever an alarm condition is sensed, the microprocessor on the control card, rechecks the alarm at 20 millisecond intervals. If the alarm exists for 12 out of 15 cycles, then it is considered a valid alarm. The control card then provides an alarm signal to turn on the WHEEL WELL FIRE light on P3, the MASTER WARNING lights on P7, and the warning electronics unit (WEU) (AMM 31-51-00/001) to sound the fire bell in the flight compartment. The bell sounds until either one of the landing gear is lowered inflight. The fire alarm signals are cancelled when the fire detector cools to approximately 360 degrees
F.
(3)
An EICAS alarm output signal is also routed to the left and right EICAS computers (AMM 31-41-00/001) which provide warning alerts in the flight compartment.
(4)
Both ends of the continuous fire detection loop are connected to a detection circuit on the duct leak overheat and wheel well fire card. If a fire detector breaks (open circuit), all detectors will remain connected to the fire detection circuit and will provide the normal fire annunciation.
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MAINTENANCE MANUAL
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