Accident Sequence
During an instrument approach at night, the pilot of a twin-engine turboprop airplane reported an engine failure without specifying which engine. Approximately nine seconds later, the airplane impacted terrain about a quarter-mile short of the runway. A postcrash fire consumed most of the wreckage. In the final nine seconds of flight, the airplane's groundspeed decreased from 99 to 88 knots as it descended about 400 feet in a slight left turn before impact. The airplane's minimum controllable airspeed was 92 knots. The slowing left turn, combined with left-wing-low impact signatures at the accident site, was consistent with a loss of control just before impact.
Examination Findings
Postaccident teardown of the left engine revealed the first-stage turbine rotor had one blade separated at the midspan. The fracture surface exhibited varying levels of oxidation, and investigators could not determine whether the blade separation occurred during the accident flight or a prior flight. The second-stage turbine operated at temperatures higher than the first stage, consistent with engine degradation over time. Additionally, the second-stage turbine stator assembly was missing vane material from the six to twelve o'clock positions, consistent with thermal damage. These findings indicated reduced performance of the left engine, but not a total loss of power.
Examination of the right engine revealed no preimpact anomalies that would have precluded normal operation. Both propellers had blade angles in the mid-range and exhibited evidence of little to no powered rotation. Neither propeller was in the feathered position, as instructed by the pilot operating handbook for an engine failure.
Probable Cause
According to the official investigation, the pilot's failure to secure and feather the left engine and increase power on the right engine after a perceived loss of engine power in the left engine resulted in a loss of control and impact with terrain just short of the runway. Contributing to the accident was a reduction in left engine power due to a first-stage turbine blade midspan separation and material loss in the second-stage stator, which were the result of engine operation at high temperatures for an extended period.