What happened
A private pilot and one passenger were engaged in an 875-nautical-mile cross-country flight when the aircraft reached a cruising altitude of 24,000 feet MSL. Radar data indicates the autopilot was engaged during this phase of flight. Approximately one hour and 40 minutes into the journey, the pilot notified air traffic control of his intention to temporarily leave the frequency. This was the final radio communication received from the aircraft.
Shortly after this transmission, the aircraft entered a right bank and began a rapid spiral descent. During this descent, the aircraft suffered an in-flight breakup, with portions of the wings, elevators, and horizontal stabilizers separating from the airframe. The aircraft subsequently impacted the ground in a largely unpopulated hilly region. There were two fatalities resulting from the accident.
Findings
Investigations into the wreckage and flight data determined that the aircraft's descent became so severe that it exceeded the design stress limits of the aircraft type, leading to the structural failure. Examination of the engine and surviving primary components showed no evidence of mechanical malfunction or failure that would have prevented normal operation. Prior to the incident, the pilot's flight logs showed engine parameters were consistent with normal operation.
Environmental conditions at the time of the accident included clear visibility below the cruising altitude, as clouds were well below the flight path, and no turbulence was reported in the area. While the aircraft was equipped with an autopilot system and manual overrides, it is believed that the pilot may have inadvertently disconnected the autopilot while attempting to attend to something in the cabin after requesting to leave the frequency, leading to an unrecoverable upset.