G. The three speed brake test switches check the speed brake indicating circuit for continuity. The test switches simulate failures that the speed brake indicating system must annunciate. This proves the speed brake indicating system is operative, but does not verify if the speed brake system is operative. If continuity exists when any of the test switches are actuated, the SPEED BRAKE ARMED light extinguishes and the SPEED BRAKE DO NOT ARM light illuminates. Actuating test switch No. 1 simulates a short-to-power failure of a wheel speed relay. This applies a voltage at a point where a subsequent failure could raise the speed brakes. Actuating test switch No. 2 simulates a failed-closed (ground on the indicating system) position of a wheel speed relay. Actuation of test switch No. 3 simulates a failure with an engine thrust lever advanced far enough to actuate one of the thrust lever actuated switches. This applies a voltage at a point where a subsequent failure of a wheel speed relay would raise the speed brakes if the speed brake control lever is in the ARMED position, and cause the aural warning horn to sound if the airplane is on the ground and not in takeoff configuration.
H. If the speed brake control lever is manually placed in the up position when airplane speed is below 60 knots and both ground and air sensing relays have been in ground mode in excess of 4 seconds, the wheel rotation signal will not be sufficient to automatically extend the speed brake lever actuator and the speed brake lever actuator position limit switch will remain in speed brake down or lever down and locked position. If engine No. 1 or 2 thrust lever is subsequently advanced far enough to actuate a thrust lever actuated switch, the electrical circuit to move the speed brake lever actuator automatically to the down position will not be completed, and the takeoff warning horn will sound. The speed brake lever must be moved manually to retract the speed brakes and silence the warning horn.
I. The speed brakes will automatically extend during a refused takeoff (RTO) when the thrust levers are moved to idle position and the reverse thrust levers are moved to reverse thrust position.
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Aug 15/77 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 27-62-0 Page 17
SPEED BRAKE CONTROL SYSTEM - TROUBLE SHOOTING
1. General
A. The following items should be noted before trouble shooting the speed brake system:
(1)
Spoiler switches on the overhead panel shut off hydraulic power to inboard and outboard flight spoilers. Ground spoilers are not affected by spoiler switches.
(2)
Spoiler shutoff valves are motor operated. Moving the switch will not move the valve unless electrical power is available at the valve.
(3)
Aileron trim control wheel should be set at zero during any check of spoiler/speed brake system.
