1.4 1.8 1.50 1.28 TAT + 12c 1.8 1.4 1.50 1.28
1.0 1.0
& CAUTION 54.2 EPR 54.2
WARNING
428 428
EGT
BRAKE
SOURCE a
EICAS DISPLAY UNIT
Hydraulic Brake System Indication
Figure 4
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(3)
Two accumulator pressure gages are provided. One direct reading pressure gage is installed at the accumulator charging valve location in the lower fuselage (Ref 12-15-04). The other indirect reading pressure gage is installed in the pilots P3 panel (Fig. 3), Detail B). The gages indicate the brake system nitrogen precharge pressure in the accumulator. The pressure signal for the P3 panel gage originates at a transducer adjacent to accumulator and is sent to the brake pressure sensing indicator and gage in the flight compartment.
(4)
In addition to the above indicators the brake system interfaces with the Engine Indicating and Crew Alerting System (EICAS) ( Detail C) to provide various caution messages. These messages include BRAKE SOURCE for low left and right hydraulic system pressure.
3. Operation
_________
A. Brake Hydraulic System Functional Description (Fig. 5, 6)
(1)
The normal brake system is powered from the right hydraulic system and the alternate system is powered from the left hydraulic system. The brake system accumulator (passive source) in the right hydraulic system provides pressure after the active brake pressure sources are lost. Left hydraulic system pressure is automatically selected on loss of right hydraulic system pressure (48 percent or less of normal pressure). The brake accumulator is selected automatically after loss of right and left hydraulic systems (48 percent or less of normal pressure in both systems).
(2)
A reserve brake power source may be manually selected if the above sources are unavailable. Pressing the RESERVE BRAKES switch on the flight compartment P1 panel provides a dedicated supply of hydraulic fluid from the right hydraulic system reservoir to hydraulic brake system supply lines. The dedicated supply of hydraulic fluid is obtained by opening of a standpipe selector valve to the right hydraulic system reservoir. The brake lines are isolated from other hydraulic loads in the right system and an electric motor-driven hydraulic pump is energized.
(3)
Metered pressure to the brakes is supplied either manually, through the brake metering valves, or automatically, through the autobrake valve.
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MAIN GEAR
LEFT HYD POWER
04
1 2 3 RIGHT HYD POWER SELECTOR VALVE
ACCUMULATOR(UP PRESS)
GAUGE
PRESS
PSI X 1000
ALTERNATE BRAKE
SELECTOR VALVE
ACCUMULATOR
TO HYDRAULIC
BRAKE SOURCE
XDCR (FIG. 5)
ACC ISOL VALVE HYD BRAKE SYSCONTROL & INDCHARGING
(TO ALTN VLV SELVALVE
PRESS SWITCH)
RUDDER
RUDDER
PEDAL INPUT
PEDAL INPUT AUTOBRAKEVALVE MODULE
750
P 750P
TO
PSI TO ANTISKID/PSI
ANTISKID/ AUTOBRAKEAUTOBRAKE
CONTROL
CONTROL
SYSTEM
SYSTEM
NORMAL VALVE
NORMAL VALVE AUTOBRAKE
AUTOBRAKESHUTTLE VALVE
SHUTTLE VALVE
SEE FIG. 5PARKING
FOR ELECTRIC BRAKE
OPERATION OFVALVEVALVE WHEELBRAKEACTUATOR
ALTERNATE VALVE ALTERNATE VALVE WHEEL BRAKE ACTUATOR
R BRAKE METERINGMODULEL BRAKE METERING VALVE
VALVE MODULEL ALTERNATE
R ALTERNATE RETRACT PRESSURE
ANTISKIDANTISKIDVALVEL NORMALR NORMALVALVEMODULE ANTISKID VALVEANTISKID VALVE
MODULE MODULEMODULE
L ANTISKIDR ANTISKIDSHUTTLE VALVESHUTTLE VALVEMODULE MODULE
BRAKE HYDRAULIC SYSTEM - NORMAL BRAKES
METERED PRESSUREFWDSYSTEM PRESSURE
NITROGEN
SYSTEM RETURN
Hydraulic Brake System Simplified Hydraulic Schematic
Figure 6
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(4)
Gear retraction braking pressure is supplied through the alternate system and is controlled by left and right gear autobrake (de-spin) actuators mounted on the brake metering valves. Gear-up pressure is channelled directly to the actuators to stop wheel spin prior to their entry into the wheel well.
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