Event Details
During cruise at 1,600 feet MSL on top of clouds, the left engine experienced a loss of power. The pilot attempted an in-flight restart but was unsuccessful. The engine was feathered while the aircraft diverted to Tonopah, Nevada. The aircraft was unable to maintain altitude on the remaining engine.
The last reported weather at Tonopah indicated a 400-foot broken ceiling and 800-foot overcast. Over Tonopah, the pilot executed a descending spiral in instrument meteorological conditions (IMC). During the descent, icing conditions were encountered. The aircraft broke out of the clouds at approximately 400 feet above ground level (AGL) at night, but the pilot could not see the airport. Still unable to maintain altitude, the pilot conducted a forced landing with the landing gear retracted.
Findings
Examination of the left engine revealed no pre-impact failure or malfunction. However, inspection of the left fuel selector bowl showed signs of microbiological growth. Heavy microbiological growth was also found on the left fuel filter, and water and microbiological growth were present in the left fuel tank.
Supplemental Type Certificate (STC) SA117NW required the addition of anti-icing and anti-biological additives to the fuel. No additives had been used during the previous refueling.
Probable Cause
No probable cause was stated in the source.