What happened
During a takeoff roll, an aircraft experienced a sudden and premature rotation to a high nose-up attitude. Witnesses observed that shortly after this rotation, the aircraft struck the ground tail-first followed by the nose. The aircraft subsequently veered off the side of the runway and came to rest on a taxiway. At the time of the accident, wind conditions were reported as calm. The pilot later informed witnesses that the aircraft had stalled during takeoff.
The investigation
Following the accident, investigators found that both the elevator trim tab and the cockpit elevator trim indicator were positioned in the full nose-up trim position. The pilot reported that because the aircraft had a dead battery, external power was required for the engine start. During this startup process, the autopilot cycled twice.
The pilot stated that after performing a normal run-up, he trimmed the aircraft for takeoff. He reported that upon reaching 62 knots, the autopilot moved the pitch trim to the full nose-up position, causing the aircraft to pitch prematurely and lift off the ground. The pilot then retracted the landing gear, at which point the left wing dropped and the airplane settled back onto the ground.
Technical analysis of the autopilot manufacturer's design revealed that the pitch servo capstans include a clutch intended to slip when 25 pounds of control wheel force is applied. However, flight test data provided by Piper indicated that the amount of control wheel force required to maintain a speed of 62 knots while the trim tab was at full deflection would be less than 40 pounds.