Incident Summary
During a flight, the captain was piloting the aircraft with his right hand resting on the power controls. While turning onto final approach, the airplane encountered turbulence of sufficient intensity that the captain's feet came off the rudder pedals. He felt a 'click' in his hand and immediately noted a propeller overspeed. The crew secured the engine by closing the fuel shutoff valve, and subsequently performed an uneventful no-flap landing.
Post-Incident Examination
Post-incident examination disclosed that both air-ground circuit breakers were open. The left engine was found to be functionally destroyed. A readout of the digital flight data recorder provided detailed performance data.
Flight Data Recorder Analysis
The digital flight data recorder data indicated that the maximum left propeller rpm reached 150.49%, while the right propeller reached 120.4%. Vertical acceleration values ranged from 0.647 G to 1.26 G, and longitudinal acceleration values ranged from 0.037 G to 0.096 G. The right engine torque peaked at 37%, whereas the left engine torque remained at 0%. Right engine fuel flow was 16% to 19% lower than left engine fuel flow. Additionally, propeller imbalance values for the left engine were approximately 50% higher than those recorded for the right engine.