Incident Overview
During a cruise flight, a pilot with 33,000 hours of flight experience reported encountering "extreme clear air turbulence followed by three jolts in rapid succession." According to the pilot's statement, he heard a loud pop as he moved the throttle to the flight idle position. As airspeed decreased, the pilot attempted to increase power but found that the throttle would not move from the flight idle position. Simultaneously, the propeller entered the BETA range.
Aircraft Behavior
The airplane pitched downward as the pilot continued efforts to push the throttle lever forward. During this event, the aircraft established a rate of descent exceeding 10,000 feet per minute at a near-vertical attitude. The pilot subsequently initiated an evacuation of the airplane and deployed his sport parachute, which he was wearing during the flight. The airplane then impacted terrain.
Post-Accident Inspection
A post-accident examination of the airframe, propeller, and engine revealed no mechanical anomalies that could have caused the accident. The reason for the loss of propeller pitch control could not be determined.
Probable Cause
The official probable cause is the loss of propeller pitch control for undetermined reasons.