What happened
While on final approach, the captain was operating the aircraft with his right hand resting on the power controls. The aircraft encountered turbulence of enough intensity to cause the captain's feet to come off the rudder pedals. During this event, the pilot felt a click in his hand, followed by an instantaneous propeller overspeed.
The crew eventually secured the engine by closing the fuel shutoff valve. The aircraft subsequently completed an uneventful landing without the use of flaps.
The investigation
Post-incident examination revealed that both the air and ground circuit breakers were in the open position. The left engine was found to be functionally destroyed.
Data from the digital flight data recorder provided the following technical details:
- Maximum propeller RPM reached 150.49% for the left engine and 120.4% for the right engine.
- Vertical acceleration values ranged from .647 to 1.26 G's.
- Longitudinal acceleration values ranged from .037 to .096 G's.
- The right engine torque peaked at 37%, while the left engine torque remained at 0%.
- Right engine fuel flow was between 16% and 19% lower than the left engine fuel flow.
- Propeller imbalance values for the left engine were approximately 50% higher than those recorded for the right engine.