What happened
The flight crew initially feathered and secured the left engine and propeller due to low oil pressure. In response to this emergency, the pilot diverted the aircraft to an alternate airport.
During the final approach in a landing configuration, the pilot applied power; however, the right engine produced only approximately 40% torque. After unsuccessful attempts to correct the power deficiency, the pilot retracted the landing gear and ditched the aircraft.
The investigation
An examination of the left engine nacelle revealed an oil leak from an unidentified source that had depleted the oil supply.
Investigators also checked the operational status of the right engine's condition and power levers. They found that the fuel control concentric shaft control linkage assembly was "stiff," and the linkage at the propeller governor failed to move when the condition lever was manipulated. Investigators could not determine why the propeller governor failed to respond to the condition lever movement.
To further investigate, the right engine was removed for an engine run, during which it operated normally. Subsequent testing of the propeller governor and propeller pitch control also showed normal operation.
Maintenance records indicated that the last annual inspection occurred on March 5, 1984. A 100-hour airframe inspection had been completed only 2.3 flight hours prior to the accident. However, the engine logbooks were not located for review.