(8)
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747-400 MAINTENANCE MANUAL
(c) Any thrust lever switch shows advanced on the ground.
NOTE:____ At touchdown Any thrust lever that shows advanced for
three seconds or less will not disarm the autobrake.
(d) Any autobrake malfunction detected by the BIT.
(e) Any antiskid malfunction detected by the normal antiskid system
except for malfunction of antiskid channels that have been
turned off using the switches on the front of the brake system
control unit.
(f) The spoiler handle moved to the stowed position.
(g) The IRS signal has not been received by the autobrake system or
the signal is not recognized.
Autobrake RTO arming logic
(a)
Power to the autobrake RTO control logic is supplied through the RTO position on the autobrake selector switch and the switch will latch into the RTO position after these conditions varified: 1) RTO autobrake selected (supplies power). 2) No malfunction found in the autobrake RTO logic circuits
and inputs. 3) Both air/ground signals show ground mode. 4) No malfunctions in the normal antiskid system are detected.
(b)
If any of the above conditions are not verified the autobrake selector switch will automatically move from the RTO to the OFF position.
Autobrake RTO application logic
(a)
The solenoid valve and the control servo valve fully open when these conditions occur: 1) Autobrake RTO system is armed. 2) The RTO spinup logic circuit is latched (wheel speed higher
than 85 knots). 3) All thrust lever signals show idle thrust. 4) No malfunctions of the autobrake or normal antiskid system
are detected.
NOTE: These malfunctions will not disarm the autobrake
____ when operating in the RTO mode:
-Loss of IRS signal input
-Left or right autobrake-shuttle-valve-pressure
switch shows high pressureAutobrake RTO disarm logic
(a) In the RTO mode the autobrake will disarm when one of these conditions occur: 1) The autobrake selector switch is moved to the OFF position. 2) One of the air/ground signals from the PSEU changes to the
air mode.
NOTE: Power is removed from the switch solenoid and the
____ switch turns to the OFF position.
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747-400 MAINTENANCE MANUAL
(b) The autobrake will disarm after RTO brake operations begin if one of these conditions occur:
NOTE: The AUTOBRAKE advisory indication will come into view on
____ EICAS but the autobrake selector switch will not turn from RTO to the OFF position.
1) One or more of the thrust lever switches show out of the idle position. 2) The rudder/brake pedals are pushed far enough to operate
the brake pedal bus switches (disarm to manual braking). 3) An autobrake or antiskid malfunction occurs. 4) The speedbrake handle is moved to the stowed position.
(c)
The AUTOBRAKES advisory indication will remain on until the selector switch is turned to the OFF position or the air/ground signals change to the air mode.
(9)
Autobrake System Outputs and Indication
(a)
The autobrake logic circuits in the brake system control unit transmit signals to operate the solenoid valve and the servo control valve in the autobrake pressure control module. The servo control valve will control pressure put to the brakes to get a constant deceleration rate until the airplane comes to a complete stop. If either member of the flight crew manually operates the brakes or the system disarms because of a malfunction, brake pressure will be removed. The brakes will also release but the system will not disarm if the airplane returns to the air mode after touchdown. The deceleration selection may be changed during the landing roll without a system disarm.
(b)
Autobrake indication is an AUTOBRAKES advisory message on EICAS when ever there is a malfunction causing a system disarm. If the autobrake selector switch is in the OFF position and an AUTOBRAKES advisory message comes into view on EICAS, the solenoid pressure switch in the autobrake control module is signaling high pressure (solenoid valve open). This is an indication of a solenoid valve or a pressure switch malfunction. When the selector switch is moved from RTO to OFF after an autobrake system disable, the AUTOBRAKES message will stay in view for 45 seconds.
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