31-41-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (4)  
Automatic In-Flight Zero Recalibration

 (a)  The WBC initiates an in-flight zero recalibration procedure when specified conditions are met. This recalibration procedure corrects load sensor zero values which may have shifted since the last flight leg. The new zero values are stored in the CM.

 (5)  
Cargo Loading Interface

 (a)  
During airplane cargo loading, the WBC uses the computed value of center of gravity or nose gear load weight and a limit (programmed into the WBC from the front panel keyboard) to determine an airplane tipping condition. The WBC sends a tip alarm output discrete to the cargo loading system if it determines a tip condition.

 (b)  
The WBC uses built-in tests to determine specific system faults. If these tests find that gross weight and center of gravity cannot be computed correctly, the WBC outputs a cargo system disable analog discrete signal to the cargo loading system.

 B. Control
 (1)  
Primary power for the WBC is 400 Hz, 115 volts ac obtained from the ground service bus through the WT & BAL circuit breaker on P414 Power Distribution Center - Left. Excitation voltage for the load sensors, pitch attitude sensor and calibration module is supplied by the WBC.

 (2)  
Alternate power for the WBC is 400 Hz, 115 volts ac obtained from the cargo handling bus through the WBS CHB ALT circuit breaker on P415 Power Distribution Center - Right.

 (3)  
Under normal circumstances the following is the sequence of operation for the weight and balance system: turn system on, operate system until the loading operation is complete, turn system off. The gross weight and center of gravity can be monitored from the CDUs.

 (4)  
The cargo loading system receives signals for airplane tip condition and WBC integrity.

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 31-41-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400
FAULT ISOLATION/MAINT MANUAL

WEIGHT AND BALANCE SYSTEM
COMPONENT  FIG. 102 SHT  QTY  ACCESS/AREA  REFERENCE AMM 
CIRCUIT BREAKER - 117AL, MAIN EQUIP CTR, P414 
WT & BAL, C10503  1  414K20  * 
CIRCUIT BREAKER - 117AL, MAIN EQUIP CTR, P415 
CARGO HANDLING CONT MN DK, C1409  1  415F18  * 
WBS CHB ALT, C10866  1  415G21  * 
COMPUTER - WT AND BAL, B7110  1  1  117AL, MAIN EQUIP CTR, E2-4  31-41-01 
COMPUTER - (FIM 34-61-00/101) 
L FLIGHT MANAGEMENT, M7442 
R FLIGHT MANAGEMENT, M7443 
MODULE - CALIBRATION, M7293  1  1  117AL, MAIN EQUIP CTR, E2-4  31-41-04 
RELAY - WBS ALT PWR SOURCE, R8664  1  1  117AL, MAIN EQUIP CTR, P414  * 
SENSOR - PITCH ATTITUDE, T1454 1  1  117AL, MAIN EQUIP CTR  31-41-03 
SENSOR - LOAD 1, T1420  2  1  L WING GEAR, FWD OUTBD  31-41-05 
SENSOR - LOAD 2, T1421  2  1  L WING GEAR, FWD INBD  31-41-05 
SENSOR - LOAD 3, T1422  2  1  L WING GEAR, AFT OUTBD  31-41-05 
SENSOR - LOAD 4, T1423  2  1  L WING GEAR, AFT INBD  31-41-05 
SENSOR - LOAD 5, T1424  2  1  L BODY GEAR, FWD OUTBD  31-41-05 
SENSOR - LOAD 6, T1425  2  1  L BODY GEAR, FWD INBD  31-41-05 
SENSOR - LOAD 7, T1426  2  1  L BODY GEAR, AFT OUTBD  31-41-05 
SENSOR - LOAD 8, T1427  2  1  L BODY GEAR, AFT INBD  31-41-05 
SENSOR - LOAD 9, T1428  2  1  R BODY GEAR, FWD INBD  31-41-05 
SENSOR - LOAD 10, T1429  2  1 R BODY GEAR, FWD OUTBD  31-41-05 
　
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