What happened
The flight originated in Minneapolis, Minnesota, with scheduled stops including Kansas City, Missouri, and Tulsa, Oklahoma. During a crew change in Kansas City, it was noted that the left engine torque meter pressure indication was approximately 90 PSI, significantly lower than the standard 145 PSI. This discrepancy was disregarded for the remainder of the flight.
Upon arrival at Tulsa, the aircraft experienced an issue where the left propeller moved to a full feathered position and the engine stopped during the transition from reverse thrust to positive thrust while taxiing. Although the engine was successfully restarted for the departure from Tulsa, the takeoff proceeded with 29 passengers and a flight crew of four.
The aircraft departed Tulsa at 1302LT using Runway 12 with flaps set at 24 degrees. Shortly after the landing gear was retracted at an airspeed of approximately 145 mph, the left engine torque meter assembly failed. This failure caused the left propeller to automatically feather and begin rotating slowly. The crew felt a severe vibration and a momentary yaw to the left.
Attempting a single-engine climb, the aircraft reached a maximum altitude of about 150 feet before airspeed dropped to 124 mph. To avoid an obstacle, the pilot initiated a shallow left turn. During this maneuver, the flaps were retracted from 24 degrees toward 12 degrees. As the airspeed fell to 107 mph, the aircraft lost altitude steadily, eventually striking a grove of trees approximately 17 feet above the ground and sliding on its fuselage. The aircraft was destroyed by fire, but all occupants evacuated safely.
Findings
- The left engine torque meter pressure indication was abnormally low prior to takeoff.
- A failure in the left engine torque meter assembly triggered the automatic feathering of the propeller.
- The retraction of the flaps from the takeoff setting at a critical airspeed contributed to the loss of lift and subsequent descent.