What happened
During the initial climb phase, approximately 500 feet above the ground, the left engine of the aircraft experienced a loss of power while maintaining a speed of 120 knots with the landing gear retracted. In response to the failure, the pilot feathered the propeller and adjusted the aircraft's attitude to maintain a level descent. The pilot initiated a shallow left turn toward the departure airport, noting a descent rate between 200 and 300 feet per minute while maintaining 20° of flaps.
After successfully clearing nearby trees, the pilot extended the landing gear and transitioned into a right bank to align with the runway, increasing the flaps to 40°. Upon touchdown, the pilot engaged single-engine reverse thrust. The aircraft subsequently veered off the right side of the runway and entered a ditch, which caused the collapse of both the nose and right main landing gear.
Findings
An inspection of the engine identified that the torque sensor housing had failed, which interrupted the drive to the fuel pump. A metallurgical analysis determined that the housing arm of the torque sensor had succumbed to fatigue failure.
Records indicate that a service bulletin had been released on September 14, 1979, recommending the replacement of the original torque sensor housing with an upgraded version due to resonant vibrations that caused cracking in the assembly. Although the engine had undergone an overhaul in December 1979, the required service bulletin was not implemented. Additionally, the investigation noted that the pilot did not adhere to prescribed engine failure procedures or recommended airspeeds, specifically noting that the flight manual advised against using 40° of flaps during single-engine approach and landing operations.