Background
The pilot departed on a cross-country flight. About 20 minutes after departure, the pilot acknowledged a clearance to climb to 17,000 feet mean sea level (msl). Radar data showed the airplane reached a maximum altitude of 16,800 feet msl before entering a right descending turn followed by a left descending turn.
Accident Sequence
During the left turn, the pilot informed the controller, “I lost my autopilot; I’m in an unusual attitude.” The pilot repeated this information two more times in response to controller transmissions. The pilot’s last transmission stated he was busy trying to recover the airplane. Witnesses heard the airplane flying overhead for several minutes but could not see it due to the low ceiling.
Examination Findings
A postaccident examination of the airplane revealed no preaccident mechanical malfunctions or failures with the engine that would have precluded normal operation. Examination of the autopilot system disclosed a loose screw inside the pitch servo housing. The screw was one of two that secured the high wattage resistor to the solenoid housing. Corrosion within the screw threads was consistent with the threads not being engaged in a nut or other internally threaded feature. No mechanical damage or arcing was visible on the screw, and the operational impact of the loose screw was unknown.
Pilot Information
The pilot’s instrument flying proficiency could not be determined. According to log records, the pilot last flew 4.5 months before the accident. The airplane was in instrument meteorological conditions when the pilot stated he was trying to recover from the unusual attitude. The pilot did not follow prescribed procedures for an autopilot malfunction.
Weather and Toxicology
Weather data indicated the airplane most likely encountered turbulence and icing conditions during the flight; however, the airplane was equipped with an ice protection system. Toxicology tests found ethanol, but the levels varied greatly among tissue/fluid samples, and the investigation could not determine if the ethanol resulted from ingestion or postmortem production or contamination. The detected level of diphenhydramine, an over-the-counter sedating antihistamine used to treat allergies, was above therapeutic levels and likely contributed to the pilot’s inability to recover from the unusual attitude.