(5)  
Autobrake system simplified (Fig. 14)

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MAINTENANCE MANUAL

CONTROL UNIT  BRAKES(TYP 8 PLS)

SYSTEM PRESSURE
METERED PRESSURE

RETURN
OPERATIONAL DURINGMANUAL BRAKING
Autobrake System Simplified
Figure 14

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MAINTENANCE MANUAL

 (a)  
The AUTOBK ANTISKID TEST IND 1 and AUTOBK ANTISKID TEST IND 2 circuit breakers on P11 provide 28 v dc power thru the AUTOBRAKES selector switch to the control unit. An autobrake card in the unit compares IRS deceleration data inputs with the selected deceleration (encoded in the control unit). This results in a pressure command to the autobrake valve. The valve provides the pressure via the normal antiskid valves to the brakes. Two autobrake shuttle valves shuttle pressure between the normal brake metered pressure output (manual) and the autobrake pressure output. When the metered pressure > 750 psi, either the left or right shuttle valve pressure switch opens. This results in an open circuit signal to the control unit to disarm the system.

 (b)  
Both AUTOBK ANTISKID TEST IND 1 and AUTOBK ANTISKID TEST IND 2 circuit breakers on P11 simultaneously provide 28 v dc power for the BITE functions. The control unit provides fault signal to the AUTOBRAKES light and the EICAS display via the EICAS computers.

 (c)  
Inputs to the control unit affecting autobrake functions include IRS data, air/ground signal, and thrust lever and spoiler handle position signals. A working antiskid system is required for autobrake operation.

 (6)  
Autobrake control schematic (Fig. 15)

 (a)  
Autobrake system inputs