What happened
While operating in the cruise phase of flight, the aircraft encountered severe clear air turbulence characterized by three rapid, heavy jolts. During this period of instability, the pilot moved the throttle to the flight idle position, at which point an audible pop was heard. As the pilot attempted to increase power to compensate for decreasing airspeed, the throttle became stuck in the flight idle position, causing the propeller to enter the beta range.
Following this mechanical failure, the aircraft entered a steep, near-vertical dive with a descent rate exceeding 10,000 feet per minute. The pilot, who was wearing a sport parachute during the flight, initiated an emergency evacuation and successfully deployed the parachute. The aircraft subsequently struck the ground.
Findings
Post-accident inspections of the engine, propeller, and airframe revealed no mechanical defects or anomalies that would account for the incident. Investigators were unable to identify the specific reason why the propeller lost pitch control and transitioned into beta mode.