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Autopilot disengage lights are controlled by sensing circuits in the autopilot control panel and the self-test switches on the yaw damper coupler, pitch channel and roll channel. Flashing of the lights is controlled by a flasher module in the autopilot accessory box. Improper operation of the lights will therefore involve one of the three control sources (Ref Autopilot Disengage Lights Trouble Shooting Chart).
(10)
Before trouble shooting the autopilot system, ensure hydraulic and electrical power is applied to the airplane and the control surfaces operate normally without the pitch or roll channels engaged. Ensure the master caution, master dimming bus indicator lights, dim and test, autopilot warning light, pitch and roll channel circuit breakers are closed. The autopilot stabilizer trim circuit breakers should be open. Ensure the navigation receivers, air data computer and low range radio altimeter (if installed) are operative; the compass system and attitude reference systems must also be operative (Ref Chapter 34, Navigation). To prevent misleading indications, test operation of all system lights by pressing lenses to assure bulbs illuminate. The autopilot stabilizer trim warning light can be ignored when the pitch channel is engaged. Readings taken on the pitch and roll channel self-test switches are calibrated with no airspeed inputs to the central air data computer. Removal of black boxes and system components requires normal safety and maintenance precautions such as removal of power prior to removal of components and capping of all exposed electrical connectors.
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2. Yaw Damper Components (All except coupler P/N 4084042) NOTE: For aircraft with coupler P/N 4084042 installed (incorporating SB 27A1206), see 22-12-01.
A. Yaw Damper System Engage Trouble Shooting Chart
TROUBLE PROBABLE CAUSE ISOLATION PROCEDURE REMEDY
Yaw damper system does not engage Yaw damper system disengages when transfer bus is switched to different generator Yaw damper system disengages intermittently Coupler Autopilot accessory box Autopilot accessory box Autopilot accessory box On coupler P/N 2588880, check meter on front of yaw damper coupler. If meter does not read in red, coupler is faulty. On coupler P/N 4030952, press lamp test switch on front of coupler. If PASS FAIL lamps do not light coupler is faulty If system does not engage, autopilot accessory box is faulty Engage yaw damper system and verify faulty by switching generator supply to 115-volt ac transfer bus. If yaw damper disengages, auto- pilot accessory box is faulty NOTE: Yaw damper disengage light illuminate for 2 seconds when power is switched. Engage and manually disengage yaw damper system several times, allowing approximately 30 seconds for each engagement. If system does not remain engaged during 30-second interval, autopilot accessory box is faulty Replace yaw damper coupler Replace autopilot accessory box Replace autopilot accessory box Replace autopilot accessory box
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TROUBLE PROBABLE CAUSE ISOLATION PROCEDURE REMEDY
Pitch channel does not engage (cont) Pitch CWS force transducer Check control wheel steering transducers null voltage (Ref 22-11-91, Pitch Control Wheel Steering Force Transducer). If voltage unsatisfactory, transducer is faulty Adjust or replace pitch control wheel steering force transducer (Ref 22-11-91, Pitch Control Wheel Steering Force Transducer).
B. Pitch Channel Operation Trouble Shooting Chart
TROUBLE PROBABLE CAUSE ISOLATION PROCEDURE REMEDY
Elevators kick sharply on engagement (Control column movement limit is 0.5 inch) Pitch channel disengages intermittently (Interlocks known good) Pitch channel inoperative or intermittent operation Pitch channel or control panel Pitch channel or control panel Pitch channel Autopilot accessory box Control panel Conduct self-test of pitch channel. If pitch channel fails self-test, pitch channel is faulty. If pitch channel ok, control panel is probably faulty. Replace pitch channel. Engage pitch channel. If fault persists, control panel is probably faulty. Replace pitch channel and move control column. If elevators do not respond, see Hydraulic Power Pack Component Trouble Shooting Chart If pitch channel has intermittent operation replace autopilot accessory box If intermittent fault persists, autopilot control panel is faulty Replace pitch channel. Replace control panel Replace pitch channel. Replace control panel Replace pitch channel Replace autopilot accessory box Replace autopilot control panel
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