FT. MYER, FL, USA
N721J
GATES LEARJET 24B
WHILE CLIMBING TO A CRUISE ALTITUDE OF 41000 FEET, THE PILOT ENGAGED THE AUTOPILOT AT APPROXIMATELY 29500 FEET. THE AIRCRAFT STARTED TO PITCH NOSE DOWN SEVERAL SECONDS LATER. THE PITCH TRIM SWITCH WAS TURNED OFF AND THE CIRCUIT BREAKERS PULLED. THE PILOTS WERE AIDED BY A PASSENGER AND USED ALL THEIR STRENGTH TO PULL BACK ON THE CONTROL WHEEL TO KEEP THE AIRCRAFT FROM CONTINUING TO PITCH NOSEDOWN. THE AIRCRAFT LANDED SAFELY. EXAMINATION OF AUTO- PILOT REVEALED THAT AN OVERVOLTAGE CONDITION EXISTED THAT WAS DRIVING THE STAB TRIM ACTUATOR TO THE AIRPLANE NOSE DOWN POSITION. IN ADDITION, THIS CAUSED THE AUTOPILOT EFFORT INDICATOR TO SHOW A MAXIMUM NOSE DOWN DEFLECTION. ACCORDING TO THE COPILOT'S STATEMENT, THE EFFORT INDICATOR WAS AT MAXIMUM DEFLECTION DURING THE PRE-TAKEOFF CHECK.
Source: NTSB Aviation Accident Database
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