(2)
A 3-digit numeric display to show the center of gravity.
(3)
A self-test button, when pushed, starts a test of all the display segments and discrete outputs.
(4)
An INOP light comes on to show that the cargo loading system is disabled.
(5)
A TIP light comes on to show a tail tip condition.
7. Operation
_________
A. Functional Description
(1) General
(a) The WBC uses wheel weight and pitch attitude data to compute airplane gross weight and center of gravity. It also uses individual and total tank fuel quantity inputs to calculate zero fuel weight and zero fuel center of gravity. The computed data is displayed on the front of the WBC. It can also be displayed on any CDU. The WBC receives hydraulic system pressure data which is used to compensate for the error introduced into the wing landing gear load measurement when the wing landing gear position actuators are pressurized.
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747-400
MAINTENANCE MANUAL
Weight and Balance Determination
Figure 2
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
D21412
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747-400
MAINTENANCE MANUAL
Weight and Balance System Block Diagram
Figure 3
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
M48447
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747-400
MAINTENANCE MANUAL
(2) Weight and balance computer modes
(a)
Different WBC operational modes can be accessed by using the WBC keyboard. Modes 01 thru 29 are used to display WBC data and erase fault memory. Modes 31 thru 38 are used to enter or calculate various WCB parameters. Modes 41 and 51 are used to initialize the WBC and CM, respectively, after replacement. Modes 97 and 98 are used to retrieve history data from the last 10 flight legs. Mode 99 is used to enter data into the CM.
(b)
The following modes are available: 1) Mode 01 - Show GW and CG. This mode is used to show the airplane gross weight and center of gravity. 2) Mode 02 - Show ZFW and ZFCG. This mode is used to show the airplane zero fuel weight and zero fuel center of gravity.
3) Mode 03 - Show wheel weights. This mode is used to show the weight on each wheel as measured by the landing gear load sensors connected to it.
4) Mode 04 - Show PAS pitch attitude. This mode is used to show the pitch attitude calculated from the pitch attitude sensor data.
5) Mode 05 - Show airplane type and identification code. The WBC shows the airplane type and identification code stored in the calibration module.
6) Mode 06 - Show WBS configuration (single or dual) and WBC position (A or B). This mode shows whether the weight and balance is a dual or single system. If it is a dual system, each WBC shows whether it is WBC A or WBC B.
7) Mode 07 - Show tip alarm limit. This mode is used to show the value of the CG tip alarm limit stored in the CM.
8) Mode 11 - Show LRU fault history. This mode is used to show which WBS LRUs have had failures since the last time fault history was erased. The WBC can store up to 50 faults in a non-volatile memory.
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