ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -PROTECTION MODES -1
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -PROTECTION MODES -2
Hydroplane/Touchdown Protection
Hydroplane/touchdown protection operates only on the aft wheels. This mode protects against hydroplaning and also prevents locked aft wheels during touchdown.
If the gear lever is down and aft wheel speed is 50 knots less than the ground speed, hydroplane/touchdown protection releases the aft wheels.
Hydroplane/touchdown protection indirectly protects the forward and middle wheels through locked wheel protection.
Gear Retract Inhibit
To permit gear retract braking, the antiskid system stops alternate antiskid operation for 12.5 seconds after the gear lever moves out of the DOWN position.
This permits gear retract braking to stop the wheels without antiskid brake release.
Taxi Brake Release
Taxi brake release reduces brake wear. This function releases two brakes on each truck during taxi brake operation.
The Autobrake/BITE/R-Comm card supplies a taxi brake release request to the antiskid cards when these conditions occur:
*
Average wheelspeed is less the 45 knots
*
Normal brake metered pressure is between 250 and 1800 psi.
The antiskid cards get the taxi brake release request. If the wheel speed is between 1 and 45 knots, the antiskid cards send a full brake release signal to the normal antiskid valves for the selected wheels. These valves release normal brake pressure to the brakes on one axle of each truck. The axle that releases for the left and the right trucks may be different.
The selected axle changes for each brake application when the normal brake metered pressure falls below 150 psi.
Normal brake metered pressure above 1800 psi turns off taxi brake release and permits all wheel brakes to operate.
Taxi brake release operates only in the normal antiskid system.
Brake Test and Fault Monitoring (not shown)
When the controllers get a brake release test request, they use the drivers to release all pressure to the requested brake.
The Autobrake/BITE/Comm cards monitor the controllers for antiskid fault data and send this information to AIMS for flight deck display.
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -PROTECTION MODES -2
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ANTISKID/AUTOBRAKE SYSTEM -AUTOBRAKE CONTROL -FUNCTIONAL DESCRIPTION
General
The BSCU uses the Autobrake/BITE/R-Comm card to operate the autobrake system for landing and rejected takeoff. The BITE/L-Comm card supplies alternate BITE and secondary communication for the BSCU.
Autobrake control gets power from the left and right main dc buses. This power also goes to the autobrake selector.
Functional Description
When all conditions occur to arm the system, the selector latches in a selected position and sends an input signal to autobrake control. It also sends electrical power to the thrust lever micro-switch pack.
The BSCU uses this power for thrust lever position input. When the thrust levers are at idle and all input conditions for landing or RTO autobrake occur, the BSCU energizes the enable relay.
The enable relay controls the solenoid valve that sends right hydraulic system pressure to the control valve.
The BSCU then uses the control valve to control pressure to the brake system to stop the airplane at the given decelerated rate.
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ANTISKID/AUTOBRAKE SYSTEM -AUTOBRAKE CONTROL -FUNCTIONAL DESCRIPTION
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ANTISKID/AUTOBRAKE SYSTEM -AUTOBRAKE FUNCTIONAL DESCRIPTION -LANDING ARMING LOGIC
General * AUTOBRAKE 4
*
AUTOBRAKE MAX. The selector latch solenoid holds the autobrake selector in the selected deceleration position when these arming conditions occur:
*
You move the autobrake selector to a deceleration position
(1, 2, 3, 4, MAX AUTO)
*
Air mode (the two trucks TILTED or the landing gear lever
UP), or the two thrust levers are at idle, or ground mode (the
ADIRU ground speed -the average wheelspeed is less than
50 knots) for less than three seconds
*
Left and right normal brake metered pressure is less than
1500 psi
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