Accident Overview
An aircraft crashed after entering a near-vertical nose-down descent during cruise flight. Witnesses reported the aircraft pitched down abruptly. The pilot had earlier flown with an instructor, who had to recover control after the pilot allowed the aircraft to enter an uncommanded spiral. During that instructional flight, a radio transmission noted, "Problems with the HSI we, ah, need to come back."
Events Prior to Accident
The pilot had been scheduled to fly to Louisville, but that flight was canceled. Later the same day, the pilot (who was also the aircraft owner) returned to the airport, stating he had read about the HSI system and wanted to reset it and fly. Shortly after takeoff on the accident flight, the pilot radioed that the autopilot was "stuck. It is taking main strength to hold it." He expressed a desire to talk to someone knowledgeable about the Bonanza to "see what he could do."
Autopilot and Trim Tabs
The aircraft's autopilot, when disconnected, produces an audible sound. No such sound was heard on recorded audio from the accident flight. Subsequent examination of the wreckage found the trim tabs in the full nose-down position. A pilot who had flown the same aircraft the previous day reported that the autopilot would not disconnect using the mode off switch.
Investigation Findings
No probable cause was stated in the source material. The investigation noted the pilot's earlier control issues, the reported autopilot malfunction, and the trim tab setting. The accident sequence involved a loss of pitch control leading to a vertical descent.