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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
SEE A
BRAKE METERED
HYDRAULIC PRESSURE
PRESSURE LINE
LINE
PRESSURE
SWITCH
SHUTTLE AUTOBRAKE
VALVE
HYDRAULIC
PRESSURE LINE
____ LH AUTOBRAKE SHUTTLE VALVE SHOWNNOTE: RH SIMILAR.
A
Autobrake Shuttle Valve Location Figure 8
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
B. The major components of an autobrake shuttle valve are a shuttle valve and a pressure switch. The shuttle valve has three hydraulic ports and a pressure switch port. The hydraulic port marked A IN is connected to a brake metering valve. The hydraulic port marked B IN is connected to the autobrake pressure control module. The hydraulic port marked OUT is connected to an antiskid valve module assembly. The pressure switch is installed in the pressure switch port and monitors pressure from the brake metering valve. In relation to the autobrake system, this pressure switch is referred to as the brake metered pressure switch.
C. The two shuttle valves are used to connect the antiskid valve module assemblies with the source of brake metered pressure that is in operation. At the same time, the shuttle valves isolate the source of brake metered pressure that is not in operation. The shuttle valve allows the highest inlet pressure, the pilots metered or the autobrake, to pass through to the brake system. In the normal brake hydraulic system, the sources of brake metered pressure are:
(1)
The autobrake pressure control module
(2)
The normal brake metering valves.
D.
The brake metered pressure switch contains a single-pole double-throw switch.
(1)
When the pressure on a piston in the pressure switch is approximately 750 psi or more, the switch will operate. When the pressure on the piston decreases to approximately 450 psi or less, the switch will return to the low pressure configuration.
E.
Operation of a brake metered pressure switch with the autobrake system armed will cause the autobrake system to disarm. Manual brake operation is then possible.
F.
The CMC can isolate a fault of a brake metered pressure switch during the system BITE test. The brake metered pressure switch can be replaced independently of the shuttle valve. The shuttle valve and the brake metered pressure switch can also be replaced together. No adjustment or repair of the shuttle valve or the pressure switch is possible when these components are installed on the airplane.
11. Brake Pedal Bus Switch (Fig. 9)
______________________
A. The brake-pedal-bus switches operate only in the autobrake RTO mode. They disarm the RTO autobrake system when the captain or first officer push on the brake pedals to an angle greater than 12 degrees. The brake-pedal-bus switches are thus used to make sure that the brakes are applied manually to full force before the autobrake system disengages. This permits a smooth transfer of control.
B. The brake-pedal-bus switches are installed below the flight deck floor on a bracket forward of the brake pedal busses. One switch is forward of the left brake pedal bus and the other is forward of the right brake pedal bus.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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