CEN12FA487 · Mooney Airplane COMPANY, INC. M20TN

The pilot reported that the airplane, with its autopilot engaged, experienced a "violent pitch-up" without warning while it was climbing through about flight level 180. Extreme forward yoke pressure (the pilot estimated between 100 and 150 pounds force) was required to keep the airplane from pitching up and stalling, so the pilot kept both hands on the yoke.

The Airplane Flight Manual contains emergency procedures for use in the event of an autopilot out-of-trim event; the third item on the checklist directs pilots to re-trim the pitch, if necessary, using the trim wheel. The pilot noted that he did not attempt to use the manual trim wheel to change the airplane's pitch attitude because that would have required him to release hand pressure on the control yoke. He was uncertain when or how the autopilot was disengaged. He declared an emergency and made a spiraling descent to lose altitude. He reported that he encountered multiple violent pitch up and down oscillations near the bottom of the descent; the pilot's seat was broken during one of the oscillations, which allowed the pilot to use his knees to apply forward yoke pressure. He stated that by using his knees to control the yoke, the airplane was "quasi-stable," pitch oscillations still occurred due to the lack of precise pitch control. While still having difficulty controlling the airplane's pitch with the electric nose pitch trim in the full up position, he prepared for an emergency landing. The pilot used his knees to provide forward yoke pressure as he landed the airplane about 450 feet short of the runway. The airplane's nose gear collapsed, the main landing gear were sheared off, and the airplane skidded about 900 feet before coming to rest to the left of the runway. The duration of the flight from the initial pitch up event to landing was about 27 minutes. Three separate examinations of the airplane's flight controls and autopilot system found no anomalies with the autopilot system or an explanation for the violent nose-pitch-up event. The Emergency Section of the Airplane Flight Manual (AFM) supplement for the autopilot stated that for an Autopilot Out of Trim emergency the pilot should: 1) disengage the autopilot 2) maintain/regain aircraft control, and 3) pitch trim...re-trim if necessary using the trim wheel.

Verbatim NTSB analysis and probable cause from the NTSB dataset