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A
747-400 MAINTENANCE MANUAL
WHEEL WELL OVERHEAT DETECTION SYSTEM - ADJUSTMENT/TEST
______________________________________________________
1. General_______
A. This procedure has the adjustment and the operational test of the overheat detection system for the wheel wells.
B. The overheat detection system for the wheel wells is a continuous and closed loop system of four fire detector elements. The equipment numbers for the four elements are M691, M692, M693, and M694. These elements are found in the wheel wells for the left and right wing, and the two body landing gear. Each element monitors the wheel well for heat or fire.
C. When the detector temperature is 400 | 30°F, the detector's resistance to ground decreases which starts a control unit. The control unit causes an alarm indication to show on EICAS. The unit also turns on the two master warning lights, and turns on the aural warning unit.
TASK 26-17-00-705-001
2. Operational Test________________
A. References
(1)
AMM 24-22-00/201, Manual Control
(2)
IPC 26-17-02 Fig. 2
(3)
WDM 26-17-11, Wheel Well Fire Detection
(4)
SSM 26-17-01
B. Access
(1) Location Zone
221 Control Cabin LH
222 Control Cabin RH
C. Prepare for the Test
S 865-002
(1)
Supply electrical power to the standby AC bus (AMM 33-12-00/501).
S 865-003
(2)
Close these circuit breakers on the main power distribution panel, P6:
(a)
6C7, W/W FIRE DET AC
(b)
6H10, ENG FIRE/OVHT DET LOOP A FIRE-1 OVHT-2
D. Do the Operational Test That Uses the FIRE/OVHT Test Switch
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747-400
MAINTENANCE MANUAL
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747-400
MAINTENANCE MANUAL
WHEEL WELL FOR THE WINGWHEEL WELL LANDING GEARFOR THE BODY LANDING GEAR
SEE B
CONTINUOUS LOOP SENSORS FOR WHEEL WELL OVERHEAT
FWD
WHEEL WELL FOR THE BODY LANDING GEARB
Test of the Overheat Detection System for the Wheel Well
Figure 501 (Sheet 2)
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747-400 MAINTENANCE MANUAL
S 865-037
(1) Push and hold the FIRE/OVHT switch on the miscellaneous switch panel, M7317, on the P5 panel.
NOTE: Hold the test switch for approximately 7 seconds until the
____ EICAS message FIRE TEST FAIL or TEST PASSED shows. If you release the test switch before TEST PASSED or FIRE TEST FAIL shows, the test will not be completed.
S 865-006
(2) Make sure these indications occur:
(a)
The EICAS message TEST IN PROGRESS shows while the test operates.
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