Incident Overview
A pilot reported that after climbing approximately 500 feet following takeoff, at an airspeed of 120 knots with the landing gear retracted, the left engine lost power. The pilot feathered the propeller, lowered the aircraft's nose to the horizon, and initiated a shallow left turn back toward the airport. The flaps remained at 20° during the turn, during which the rate of descent was observed to be between 200 and 300 feet per minute.
Emergency Landing
After clearing trees, the pilot extended the landing gear, banked the aircraft to the right to align with the runway, and lowered the flaps to 40°. Following touchdown, the pilot applied single-engine reverse thrust. The aircraft subsequently departed the right side of the runway and entered a ditch, resulting in the collapse of the right main landing gear and the nose gear.
Engine Examination
Examination of the left engine revealed that the torque sensor housing had failed, causing a loss of drive to the fuel pump. A metallurgical examination of the housing arm of the torque sensor determined that it had failed due to fatigue.
Service Bulletin Compliance
On September 14, 1979, a service bulletin (SB) was issued requiring replacement of the torque sensor housing with an improved design. The manufacturer had overhauled the engine in December 1979 but did not comply with the service bulletin. The SB noted a history of resonant vibration that could cause cracks in the housing arm of the original torque sensor and gear assemblies, and it recommended replacement no later than during the next part exposure.
Pilot Actions and Procedures
Investigation revealed that the pilot did not comply with the published engine failure procedures and airspeeds. Additionally, the flight manual cautioned against using 40° of flaps during single-engine landings.