Alternate Brakes
When right hydraulic system pressure is low, center hydraulic system pressure operates the ASSV. The ASSV sends center hydraulic system pressure to the alternate brake system. The brakes can then get metered center system hydraulic pressure from the alternate brake metering valves.
Pressure in the alternate brake system operates the AIV to isolate accumulator pressure.
Reserve Brakes
The ASSV and AIV positions and operation are the same as for alternate brakes. The only difference is that the center hydraulic system uses reserve fluid and the C1 ACMP for alternate brake system pressure.
Accumulator Brakes
When both the right and center hydraulic system pressures are low, accumulator pressure opens the AIV. The brakes then get brake accumulator pressure from the normal brake metering valves.
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BRAKE HYDRO-MECHANICAL CONTROL -FUNCTIONAL DESCRIPTION
Gear Retract Braking
During landing gear retraction when the normal brake system has pressure, the ASSV sends main landing gear retract pressure to the alternate brake system. The gear retract pressure also operates the gear retract braking actuators on the alternate brake metering valves to pressurize the brakes.
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BRAKE HYDRO-MECHANICAL CONTROL -FUNCTIONAL DESCRIPTION
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BRAKE HYDRO-MECHANICAL CONTROL -INDICATION
General
The brake source light and advisory message show when the normal and the alternate brake system pressures are low. These two switches control these indications:
*
The normal brake hydraulic system pressure switch
*
The alternate brake hydraulic pressure switch.
The brake accumulator pressure indicator shows brake accumulator pressure.
Functional Description
There is no flight deck effect when normal brake system pressure is low and the alternate brake system has pressure. The BSCU uses the normal system low pressure input for control of the antiskid and autobrake systems.
When normal and alternate brake system pressures are low, the brake source light comes on and AIMS shows the BRAKE SOURCE advisory message. The BSCU also uses these inputs for control of the antiskid and autobrake systems.
Brake accumulator pressure is the only pressure source when the brake source light is on.
The indicator driver for the brake accumulator pressure indicator uses accumulator pressure transducer input to show pressure.
Training Information Point
The towing power system can supply power to the brake accumulator pressure indicator and the brake source light. See the electrical power chapter for more information about the towing power system (CHAPTER 24).
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BRAKE HYDRO-MECHANICAL CONTROL -INDICATION
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ANTISKID/AUTOBRAKE SYSTEM -INTRODUCTION
Purpose
The antiskid/autobrake system automatically controls brake metered pressure.
Antiskid System
The antiskid system monitors wheel speed deceleration and controls brake pressure to prevent skid conditions. It also releases one third of the brakes during taxi to extend the brake service life.
Antiskid functions include:
*
Skid control
*
Locked wheel protection
*
Hydroplane/touchdown protection
*
Gear retract inhibit
*
Taxi brake release.
Autobrake System
The autobrake system automatically supplies metered brake pressure to stop the airplane during landing or during a rejected takeoff (RTO).
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ANTISKID/AUTOBRAKE SYSTEM -INTRODUCTION
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ANTISKID/AUTOBRAKE SYSTEM -GENERAL DESCRIPTION
General
The antiskid system limits metered brake pressure from the hydro-mechanical or the autobrake systems to prevent wheel skid. This permits maximum braking effectiveness with any runway condition.
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