ANTISKID/AUTOBRAKE SYSTEM -FUNCTIONAL DESCRIPTION -INTRODUCTION
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -ANTISKID CARDS
General
The four antiskid cards work together in pairs to supply primary and backup antiskid control. The 1,5,9 card works with the 3,7,11 card and the 2,6,10 card works with the 4,8,12 card.
Each antiskid card has a primary and a secondary controller. The primary controller supplies the primary control for a fore-mid-aft wheel group. The secondary controller supplies backup control functions for a different fore-mid-aft wheel group.
The primary and secondary controllers monitor wheel speed data and use drivers to control antiskid valves for normal and alternate antiskid operation.
All the drivers have two power sources.
Normal Antiskid Operation
During normal antiskid operation, the primary controller controls an antiskid valve driver for each of the three wheels in the three wheel group. A secondary controller on a different antiskid card also sends control signals to the antiskid valve driver.
These drivers control antiskid valves on the normal antiskid valve modules.
Alternate Antiskid Operation
Primary and secondary control for the alternate antiskid system is similar to the normal system.
The alternate antiskid system uses two drivers on each antiskid card for valve control. One driver controls the aft wheel. The other driver controls the forward/middle pair of wheels.
These drivers control antiskid valves on the alternate antiskid valve modules.
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -ANTISKID CARDS
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -CONTROLLERS
General The Autobrake/BITE/Comm cards monitor the controllers for
antiskid fault data. They send this information to the AIMS for The antiskid cards use primary and secondary controllers to
flight deck display. supply these functions:
*
Skid control
*
Locked wheel protection
*
Hydroplane/touchdown protection
*
Gear retract inhibit
*
Taxi brake release.
Each controller uses these inputs for control:
*
Wheel speed from a fwd-mid-aft wheel group
*
Groundspeed
*
Landing gear lever position
*
Taxi brake release request from the Autobrake/BITE/Comm
card.
Each controller controls power output to three normal and two alternate antiskid valves with 0-55 milliampere current drivers.
The primary controller on each card uses current drivers on that same card. These drivers also get inputs from the secondary controller on the paired card.
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.
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -CONTROLLERS
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID FUNCTIONAL DESCRIPTION -PROTECTION MODES -1
Skid Control
Skid control compares calculated wheel speed velocity with a velocity model to control brake force. If a wheel slows down too quickly, skid control releases brake pressure until the wheel speed increases.
Skid control is available when wheel speed is greater than eight knots.
During normal antiskid operation, skid control operates for each wheel.
During alternate antiskid operation, skid control operates an aft wheel and a fwd-mid pair of wheels.
Locked Wheel Protection
Locked wheel protection compares the wheel speeds of a fore-mid-aft group of wheels.
If the slowest wheel speed is less than 30 percent of the fastest wheel speed, locked wheel protection releases pressure to the slowest wheel.
Locked wheel protection does not operate below 25 knots.
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