Tom Bishop

Pilatus PC-6 (Porter & Turbo Porter)

During cruise flight, the 33,000-hour pilot stated that the airplane encountered "extreme clear air turbulence followed by three jolts in rapid succession." He "heard a loud pop as he jerked the throttle to the flight idle position." As the airspeed was slowing, the pilot attempted to add power. The "throttle would not move from the flight idle position and the propeller went into BETA." The airplane pitched downward as the pilot continued to try and "push the throttle lever forward." The airplane established "a rate of descent in excess of 10,000 feet per minute at a near vertical attitude." The pilot initiated an evacuation of the airplane and deployed his parachute (the pilot was wearing a sport parachute during the flight). Subsequently, the airplane impacted terrain. During a post accident examination, no mechanical anomalies were noted on the airframe, propeller, or engine that could have caused the accident. The reason for the loss of propeller pitch control could not be determined.