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MAINTENANCE MANUAL

 4) Wheel spin-up circuit and brake fill a) The spin-up circuit includes a detection circuit and a latch circuit. The detection circuit activates when the average velocity of all wheels is 60 knots or greater and deactivates when the average velocity drops below 30 knots. The latch circuit latches three seconds after the airplane is on ground and the detection circuit is deactivated. The latch circuit resets (unlatches) when a ground-air transition takes place, or the autobrake system is turned off or disarmed. b) Upon initiation of autobrake control, the control commands an initial brake fill to provide brake application.
 5) Autobrake disarm logic a) The autobrake removes the power from the solenoid and control servo valve drivers and from the selector switch latch when:
 1.
System is selected off.

_

 2.
Either left or right metered pressure switch

_ indicates pressure (manual brake application) 750 psi.

 3.
Any thrust lever switch indicates advanced on the

_ ground, except that any thrust lever switch indicating advanced for up to 3 seconds after touchdown will not disarm the system.

 4.
Autobrake failure detected, including failure to

_ apply pressure (indicated by the pressure control switch) when application conditions are met and the commanded deceleration exceeds the actual airplane deceleration by more than one foot per second square for more than three seconds.

 5.
Antiskid failure on normal system detected except

_ for failures on a wheel whose indication has been deactivated by the control unit selector switch.

 6.
Spoilers stowed after having been deployed on the

_
 ground.

 7.
IRS signal not present or faulty.

_ 6) RTO autobrake arming a) The arming provides power to RTO control and RTO selector switch latch within 300 milliseconds when:
 1.
RTO autobrake selected.

_

 2.
No RTO autobrake failure detected.

_

 3.
Both air/ground signals indicate ground mode.

_ 7) RTO autobrake application a) The solenoid valve and the control servo valve fully open when:
 1.
RTO autobrake armed.

_

 2.
All thrust lever signals indicate idle thrust.

 3.
RTO wheel spin-up circuit latched.

_
_
 

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757 MAINTENANCE MANUAL
 4.  Autobrake arming and application logic are
_ satisfied with the exception of IRS failures and landing deceleration not selected.
 8)  RTO autobrake disarm
 a)  The disarm removes power from the RTO latch without indication when either air/ground signal indicates air mode or that RTO is turned off. If the RTO has been applied, it will disarm same as the other five autobrake settings except that loss of IRS will not disarm the RTO. The RTO turns on the AUTOBRAKES light without removing power from the RTO latch when the RTO is on and the autobrake output pressure is not high. When the autobrake RTO function is disarmed, the autobrake selector switch remains in RTO position, but the RTO function is deactivated as indicated by illumination of the AUTOBRAKE light.
 (7)  
Autobrake hydraulic operation (Fig. 15)

 (a)  
The autobrake solenoid valve provides on-off control of normal hydraulic system power to the autobrake valve module. When a valve driver signal from the control unit is received, the valve opens and admits system pressure to the pressure control valve. The servo valve varies the output pressure from the module as commanded by the control unit to maintain the selected deceleration. For description of the module operation, refer to Autobrake Module Operation paragraph.

 (b)  
The solenoid valve pressure switch senses the solenoid valve position (open or close). When the valve opens and admits system pressure to the module, the switch closes to show high (> 750 psi) pressure and provides an appropriate signal to the control unit. The control valve pressure switch senses the output pressure and provides an appropriate signal to the control unit for autobrake control.

 (c)  
Brake pressure output from the autobrake module positions the two autobrake shuttle valves to allow fluid flow via the normal antiskid modules to the brakes. Two pressure switches on the metered pressure port of the shuttle valves monitor manual brake pressure downstream of the brake metering valves. When manual braking effort exceeds 750 psi on either the left or right brake pedal, the switch opens and provides a signal to the control unit to disarm the system.
　
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