32-42-00
 ALL  ú ú 01 Page 2 ú Oct 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (5)  
28 vdc power is supplied to the autobrake system through the AUTO BRK circuit breaker on the P180 DC Power Distribution Panel. An AUTOBRAKE advisory message comes into view on EICAS when any malfunction including a loss of power to the autobrake logic card occurs. The CMC is used to do a test and trouble-shoot the autobrake system. A malfunction of the system can be isolated to any LRU including the brake system control unit.

 (6)  
The autobrake system contains these components:

 -
Autobrake circuit card (Brake system control unit)

 -
Autobrake Selector Switch (flight deck)

 -
Autobrake pressure control module (right wing gear wheel well)

 -
2 Autobrake shuttle valves (right & left wing gear wheel well)

 -
2 Brake pedal bus switches (below the flight deck floor)

 -
2 Brake Metered Pressure Switches (left and right body gear wheel wells).

 (7) The autobrake system requires these airplane interface inputs:
 -The antiskid system operating without malfunctions
 -IRS airplane ground speed, pitch angle, and longitudinal acceleration data (AMM 34-21-00/001)
 -Landing gear air/ground signal (AMM 32-09-00/001)
 -Thrust levers (advanced or not advanced) discrete signal (AMM 22-31-00/001)
 -Spoiler handle position (fully extended or not fully extended) signal (AMM 27-61-00/001).
 -
Central Maintenance Computer System for test and trouble shooting (AMM 45-10-00/201).

 D.
Brake Torque Control System

 (1)  
Brake torque control is supplied to each wheel independently. The brake torque control system monitors the torque signal from a sensor on each brake equalizer rod. It compares the signal with a set threshold value in the brake system control unit. When the brake torque increases to more than the threshold value, a brake release signal is sent to the antiskid valve driver. The valve driver compares the brake torque release signal with the antiskid release signal. The larger signal is sent to the antiskid valve to release pressure on the brakes.

 (2)  
Power for brake torque control is supplied through four 28 vdc circuit breakers on the P180 Main Power Distribution Panel. Each circuit breaker supplies power to the torque control circuits for one wheel on each landing gear truck. Brake torque limiter power is also supplied to the antiskid valve drivers if antiskid power is lost. This permits the brake torque limiter to operate with the antiskid off.

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 32-42-00
 ALL  ú ú 01 Page 3 ú Oct 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (3)  
The brake system control unit monitors the brake torque limiter system for malfunctions. A BRAKE LIMITER indication comes into view on EICAS when a malfunction occurs. The CMC is used to do a test and trouble-shoot the brake torque limiter system. A malfunction can be electrically isolated to a sensor or the brake system control unit.

 (4)  
The brake torque limiter system contains these components:

 -4 brake torque limiter circuit cards (brake system control unit)
 -16 brake torque sensors (1 on each brake equalizer rod)
 2.  Brake-System-Control Unit (Fig. 1)
_________________________
 A.  The brake-system-control unit supplies central processing, logic, and test functions for the antiskid, autobrake and brake torque control systems. The unit is installed on the E9 shelf (Central Equipment Center). Access is gotten through a hatch on the under side of the fuselage forward of the wing stub.
 B.  The brake-system-control unit is a box that contains these components:
 -8 interchangeable dual main wheel cards
 -4 brake torque controller cards
 -
1 autobrake card

 -
1 system BITE card

 -
1 data aquisition BITE card

 -
1 electronic component assembly

 -
2 rotary brake indication disable switches

 C.  
The Electronic Component Assembly

 (1)  The electric component assembly connects all the printed circuit cards and switches with the connectors on the back of the box or with each other as necessary.
　
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