(2)
Pressure reduction under other conditions is achieved by each wheel controlling its antiskid valve through the control unit on the basis of wheel speed history. A rapid reduction in wheel speed is interpreted as a skid.
(3)
The system controls both normal and alternate brake systems through antiskid valves. Eight normal valves control individual wheels. Four alternate valves control the lateral-pair wheels. The system also provides locked wheel and hydroplane protection.
(4)
Four circuit breakers on the overhead circuit breaker panel P11 provide 28 v dc power to the system. When power to the system fails, an amber ANTISKID fault light on pilots' overhead panel (P5) illuminates. The Engine Indication and Crew Alerting System (EICAS) display on pilots' center instrument panel will show the ANTISKID advisory message (Ref 31-41-00).
(5)
The system requires the following airplane interface inputs:
(a)
Inertial Reference System (IRS) speed data (Ref 34-21-00)
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INERTIALPARKING BRAKE VALVEGEAR REFERENCE(OPEN OR CLOSED)POSITION SYSTEMPOSITION (2)
ANTISKID
ANTISKID LIGHT ON MISC ANNUNCIATOR (P5)
ANTISKID MODULE IN L AND R WHEEL WELLS
VIA TAT + 12C
1.50 1.50
EICAS
1.81.28 1.81.52
COMPUTERS
1.4 1.4
1.0 1.0
EPR
M102 ANTISKID/AUTOBRAKE
CAUTION 10.50 10.50
CONTROL UNIT
& WARNING N1
750 750
EGT
ANTISKID
FWD
EICAS DISPLAY UNITS
TRANSDUCER (P2)IN AXLE
Antiskid System
Figure 1
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(b)
Landing gear position (down and locked or not down and locked) signal (Ref 32-61-00)
(c)
Parking brake valve position signal (Ref 32-44-00)
D.
Autobrake system (Fig. 2)
(1)
The system applies brakes automatically at touchdown when the average wheel speed reaches 60 knots. It maintains a constant pilot-selected deceleration level throughout the landing roll. The only pilot effort required is to select the desired level prior to each landing. There is no interference with normal antiskid system operation. Full manual braking is always available.
(2)
An AUTOBRAKES selector switch on pilots' center instrument panel (P1-3) provides pilots' choice of five levels (1, 2, 3, 4 and MAX AUTO) and one refused takeoff (RTO) mode of automatic braking. The system uses the main wheels average speed signal for spin up logic and the airplane IRS speed data for deceleration control. The system compares the airplane speed with the selected level of braking to generate a pressure command to the control servo valve. The valve provides the commanded pressure via the normal antiskid valves to the brakes.
(3)
When RTO mode is selected, full pressure (3000 psi) is applied to the brakes. The system can be armed only when there is no fault in either antiskid or autobrake system. The RTO mode on takeoff can be deactivated by placing the AUTOBRAKES selector switch to OFF or by operating brake pedals for > 750 psi brake metered pressure.
(4)
The AUTOBRKS/ANTISKID TEST/IND 1 and AUTOBRKS/ANTISKID TEST/IND 2 circuit breakers on panel P11 simultaneously provide 28 v dc power to the system. When power fails, an AUTOBRAKES light on pilots' center instrument panel illuminates. The EICAS display will show the AUTOBRAKES advisory message. Both AUTOBK ANTISKID TEST IND 1 and AUTOBK ANTISKID TEST IND 2 circuit breakers provide power for testing the system.
(5)
The system requires the following airplane interface inputs:
(a)
An operational (no fault) antiskid system.
(b)
IRS data
(c)
Landing gear air/ground signal (Ref 32-09-02)
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AUTOBRAKE SHUTTLE VALVE METERED
ASSY IN L AND R MAIN BRAKE PRESSURE
WHEEL WELLS MONITORING
SWITCH
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