Antiskid Protection
Antiskid protection is provided in the normal and alternate brake systems.
The normal brake hydraulic system provides each main gear wheel with individual antiskid protection. When the system detects a skid, the associated antiskid valve reduces brake pressure until skidding stops. The alternate brake hydraulic system works similar to the normal system however antiskid protection is applied to main gear wheel pairs instead of individual wheels.
Both normal and alternate brake systems provide skid, locked wheel, touchdown and hydroplane protection.
Antiskid protection is available even with loss of both hydraulic systems.
Autobrake System
The autobrake system uses hydraulic system B pressure to provide maximum deceleration for rejected takeoff and automatic braking at preselected deceleration rates immediately after touchdown. The system operates only when the normal brake system is functioning. Antiskid system protection is provided during autobrake operation.
Rejected Takeoff (RTO)
The RTO mode can be selected only when on the ground. Upon selection, the AUTO BRAKE DISARM light illuminates for one to two seconds and then extinguishes, indicating that an automatic self–test has been successfully accomplished.
To arm the RTO mode prior to takeoff the following conditions must exist:
.
airplane on the ground
.
antiskid and autobrake systems operational
.
AUTO BRAKE select switch positioned to RTO
.
wheel speed less than 60 knots
.
forward thrust levers positioned to IDLE. With RTO selected, if the takeoff is rejected prior to wheel speed reaching 90 knots autobraking is not initiated, the AUTO BRAKE DISARM light does not illuminate and the RTO autobrake function remains armed. If the takeoff is
rejected after reaching a wheel speed of 90 knots, maximum braking is applied automatically when the forward thrust levers are retarded to IDLE.
Copyright . The Boeing Company. See title page for details.
14.20.4 September 29, 2005
Landing Gear -System Description
737 Flight Crew Operations Manual
The RTO mode is automatically disarmed when both air/ground systems indicate the air mode. The AUTO BRAKE DISARM light does not illuminate and the AUTO BRAKE select switch remains in the RTO position. To reset or manually disarm the autobrake system, position the selector to OFF. If a landing is made with RTO selected (AUTO BRAKE select switch not cycled through OFF), no automatic braking action occurs and the AUTO BRAKE DISARM light illuminates two seconds after touchdown.
Landing
When a landing autobrake selection is made, the system performs a turn–on– self–test. If the turn–on–self–test is not successful, the AUTO BRAKE DISARM light illuminates and the autobrake system does not arm.
Four levels of deceleration can be selected for landing. However, on dry runways, the maximum autobrake deceleration rate in the landing mode is less than that produced by full pedal braking.
After landing, autobrake application begins when:
.
both forward thrust levers are retarded to IDLE
.
the main wheels spin–up.
Note: Landing autobrake settings may be selected after touchdown prior to
decelerating through 60 kts of ground speed. Braking initiates immediately
if the above conditions are met.
To maintain the selected landing deceleration rate, autobrake pressure is reduced as other controls, such as thrust reversers and spoilers, contribute to total deceleration. The deceleration level can be changed (without disarming the system) by rotating the selector. The autobrake system brings the airplane to a complete stop unless the braking is terminated by the pilot.
Autobrake – Disarm
The pilots may disarm the autobrake system by moving the selector switch to the OFF position. This action does not cause the AUTO BRAKE DISARM light to illuminate. After braking has started, any of the following pilot actions disarm the system immediately and illuminate the AUTO BRAKE DISARM light:
.
moving the SPEED BRAKE lever to the down detent
.
advancing the forward thrust lever(s), except during the first 3 seconds
after touchdown for landing
.
applying manual brakes.
Copyright . The Boeing Company. See title page for details.
September 29, 2005 14.20.5
Landing Gear -System Description 737 Flight Crew Operations Manual
Parking Brake
The parking brake can be set with either A or B hydraulic systems pressurized. If A and B hydraulic systems are not pressurized, parking brake pressure is maintained by the brake accumulator. Accumulator pressure is shown on the HYD BRAKE PRESS indicator.
The parking brake is set by depressing both brake pedals fully, while simultaneously pulling the PARKING BRAKE lever up. This mechanically latches the pedals in the depressed position and commands the parking brake valve to close.
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