~.................................................................. | | Application | | | | Autobrake | Delay | Deceleration | Maximum Brake | | Selection | in Seconds* | Ft/Sec. | Pressure, PSI | .................................................….................. | 1 | 0.2 | 4.0 | 1500 | .................................................….................. | 2 | 0.2 | 5.0 | 1750 | .................................................….................. | 3 | 0.2 | 6.0 | 2000 | .................................................….................. | 4 | 0.2 | 7.5 | 2400 | .................................................….................. | MAX | 0.2 | 11.0 | 3000 | .................................................….................. | RTO | 0. 0 | MAX** | 3000 | 2............…..................…................….................1 *No delay if the system is armed after touchdown.
**Maximum braking applied. Actual deceleration depends on airplane weight and runway conditions. ____________________________________________________________________
(3)
Autobrake arming logic
(a)
The system arms and latches with a magnetic latching switch when these conditions are met. 1) A deceleration selection (level 1, 2, 3, 4, or MAX AUTO)
has been set.
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747-400 MAINTENANCE MANUAL
2) No normal antiskid system malfunctions have been detected by the BIT.
NOTE: If antiskid fault indications for any wheel have
____ been turned off using the switches on the front of the brake control unit, that fault indication will not disarm the autobrake system.
3) No autobrake malfunctions have been detected by the BIT.
4) Correct IRS signals are transmitted to the brake-system-control unit (GND SPEED, PITCH ANGLE, and ACCELERATION only).
5) Brake metered pressure switches on the autobrake shuttle valves show low pressure.
6) Primary and alternate air/ground signals from the Proximity-Sensor-Electronics-Unit (PSEU) are in the air mode or all 4 thrust levers are in idle.
7) Normal brake system is pressurized.
(b)
The control unit supplies an arm hold signal to hold the switch in the position it was set when all the above conditions are verified. If the hold signal is removed the switch will be released to the DISARM position.
(4)
Autobrake application logic
(a)
The control unit supplies signals to the autobrake solenoid valve and control valve when: 1) The autobrake system is armed. 2) All thrust lever switches show not advanced. 3) Air/ground indication from the PSEU shows airplane on the
ground for more than 0.2 seconds.
4) The wheel spinup circuit is set.
(b)
Wheel spin-up circuit and brake fill
1) The spin-up circuit contains a detection circuit and a latch circuit. The detection circuit turns on when the average velocity of the wheels is 60 knots or greater and turns off when the average wheel velocity decreases to less than 30 knots. The latch circuit will set three seconds after the airplane is on the ground and the detection circuit turns on. The latch circuit will reset when the air/ground signals from the PSEU change to air mode, the autobrake system is disarmed or the autobrake system is turned off.
2) Autobrake operation begins with a brake fill command that pressurizes the brakes. The rate of pressure increase depends on airplane deceleration.
(5)
Autobrake disarm logic -The autobrake will disarm when any of these disarm conditions occur:
(a)
The system is turned off or loss power supply to autobrake switch.
(b)
Either of the brake metered pressure switches shows high pressure, which indicates manual brake operations.
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(6)
(7)
