Applicable Reference:
SDS 32-42-00-002, FIM 32-42 Task 803, SSM 32-41-11, 27-62-11, AMM 27-62-00-820-812
Discrepancy:
Anti-Skid light illuminated on takeoff, goes out at liftoff
Possible Fix:
Replace M162 Antiskid/Autobrake Control Unit, and M980 Auto Speed Brake Module
Tip:
For this problem check to see if Auto Speed Brake Control Circuit breaker is open (C440). (Anti-skid does not need this circuit breaker in to operate, it is more a indication of a shorted M980 unit).
Perform AMM 27-62-00, Speed Brake RTO Test and repeat it for each of the brake positions (LI LO RI RO). During this test, check to make sure all 4 of the blue lights on the Auto Speed Brake Module lights come on, and that the Auto speed brake actuator deploys when tested in all 4 positions.
Reason/Explanation:
During this problem the AACU had a fault recorded of ” SP CO LI indicates the left inboard wheel speed switch control disagrees with output for more than 3 seconds”. In this case it appears that the Auto Speed Brake Module had a internal short that caused the C440 Circuit Breaker to open. It appears as though that same short burned up the AACU when “The AACU sends signals to the auto speedbrake module when each wheel speed is more than 60 knots.”
“The auto speedbrake module uses the wheel speed input to operate the auto speedbrake actuator during the RTO function” Since this unit was shorted the 28VDC being sent to the Auto speed brake module, disagreed with the output for more than 3 seconds as stated in the fault code. Which correspondence with the Anti-skid light coming on during takeoff role when the aircraft reaches 60 knots and RTO is enabled. It was only during the RTO test when the AACU was placed in the position that correspondence to the fault message that the speed brake actuator would not deploy.
Thanks to Tom S. for his input !
