Piper PA-31-350 N40YR accident near Aniak, Alaska

Probable cause

A partial loss of engine power during takeoff due to a failure of the left engine's turbocharger as a result of the failure of a turbine shaft bearing. Contributing to the accident was unsuitable terrain for a forced landing.

NTSB analysis

The airline-transport-certificated pilot was departing in a twin-engine airplane that was about 130 pounds below its maximum gross weight. About 200 feet above the ground, the pilot reported a loss of engine power in the left engine and smoke was seen coming from the left engine by ground witnesses. The pilot indicated that he feathered the left engine, but that the airplane was descending and he elected to make an emergency landing on a gravel bar about .5 mile from the airport. Following the accident, the operator's maintenance personnel removed the left engine from the airframe and shipped it to an engine repair facility for examination. The airplane's left engine, which was equipped with a turbocharger, was placed on a test stand where it was started and ran, but it would not produce power (measured in manifold pressure) above ambient pressure. The engine's turbocharger was removed and replaced. A second engine run, with the new turbocharger installed, resulted in the engine developing full power. The original turbocharger was disassembled and inspected. The inspection revealed that one of the turbine shaft bearings had failed and that the turbine shaft and blades were damaged. One thrust bearing had fractured, with half of the bearing missing.

Text from the NTSB. Open the NTSB docket for ANC08LA097 for the full record.