ANTISKID/AUTOBRAKE SYSTEM -BRAKE SYSTEM CONTROL UNIT (BSCU) -INTRODUCTION
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ANTISKID/AUTOBRAKE SYSTEM -BSCU -PHYSICAL DESCRIPTION
General
The BSCU contains two different types of circuit cards:
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Antiskid card (4)
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Autobrake/BITE/Comm card (2).
Antiskid Card
The four antiskid cards each control antiskid valves to operate the antiskid functions for a set of three wheels. These cards also supply wheel speed data for the autobrake function.
Autobrake/BITE/Comm Card
Two autobrake/BITE/Comm cards operate the autobrakes, do the built in test functions, and supply the communication links to other airplane systems.
Although the autobrake system circuitry is on each of these cards, only the card in the Autobrake/BITE/R-Comm card position controls autobrake operation.
Both of the cards do the BITE functions. Each card independently monitors the antiskid and autobrake systems for faults.
The cards communicate with other airplane systems over different ARINC 629 systems buses. Each card has different communication links to the wheel control cards. They use these links to monitor and supply the antiskid system with digital, analog, and discrete inputs.
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ANTISKID/AUTOBRAKE SYSTEM -BSCU -PHYSICAL DESCRIPTION
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID MODULES -INTRODUCTION
Purpose
There are two normal antiskid modules and two alternate antiskid modules in the antiskid system.
These modules release brake pressure to prevent wheel skids.
Location
The normal antiskid modules are near the main landing gear beams outboard of the main landing gear trunnions. An access panel permits you to get access to the normal antiskid valve modules.
The alternate antiskid modules are on the main landing gear beams inboard of the main landing gear trunnions.
Normal Antiskid Modules
There are two normal antiskid modules: one for each main landing gear. The modules are the same. Each module has six valves.
The modules are LRUs and each module contains these LRUs:
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Inlet filter (2)
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System pressure shutoff valve
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Antiskid valve (6)
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Hydraulic fuse (6).
Alternate Antiskid Modules
There are two alternate antiskid modules: one for each main landing gear. The modules are the same. Each module has four valves.
The modules are LRUs and each module contains these LRUs:
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Inlet filter (2)
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System pressure shutoff valve
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Antiskid valve (4)
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Hydraulic fuse (4).
Training Information Point
The system can operate with one unserviceable normal antiskid valve for each six wheel truck. You must deactivate the related brake.
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID MODULES -INTRODUCTION
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777 AIRCRAFT MAINTENANCE MANUAL
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID MODULES -FUNCTIONAL DESCRIPTION
General
The operation of normal and alternate antiskid modules is the same. The number of antiskid valves and hydraulic fuses is the only difference in the two modules.
The normal antiskid module controls brake pressure for six wheels independently. The alternate antiskid module controls two wheels independently and two sets of paired wheels with the other two antiskid valves.
Inlet Filters
An in-line filter screen removes contamination from brake metered pressure fluid as it enters the antiskid module.
System pressure fluid also goes through a filter as it enters the antiskid module.
System Pressure Shutoff Valve
When brake metered pressure is above 225 psig, the system pressure shutoff valve supplies system pressure, if available, to the first stage of each antiskid valve. This provides a constant 3000 psi pressure level for pressure control.
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When brake metered pressure is less than 225 psig, system pressure closes the shutoff valve. This prevents wear of first stage components by constant application of system pressure. When the shutoff valve is closed, it uses metered pressure to control the first stage.
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