What happened
On May 24, 2022, a de Havill and DHC-3 Turbine Otter, registration N703TH, was operating an on-demand charter flight from Yakutat Airport (PAYA) to Dry Bay Airport (3AK) in Alaska. During the initial takeoff from PAYA, the pilot noted the tail briefly lifted and then fell back to the runway when attempting to raise the tail with forward elevator; the pilot attributed this behavior to an aft-loaded aircraft and applied additional nose-down trim.
While en route, the pilot observed the tail moving up and down, which was attributed to turbulence. During the approach to runway 23 at 3AK, the pilot entered a left downwind pattern and extended flaps to 10°. While turning final, the pilot noticed a pitch-up tendency and applied full nose-down pitch trim and further flap extension. Upon applying full flaps on short final, the aircraft abruptly pitched up to a 45° angle. The pilot applied full nose-down elevator and reduced power to idle, but at approximately 300 feet above ground level, the airplane stalled, the left wing dropped, and the aircraft entered a 45° nose-down dive. The aircraft impacted forested terrain near the approach end of the runway, resulting in 4 serious injuries and 0 fatalities.
The investigation
An examination of the airframe and engine, including an engine monitor, revealed no mechanical malfunctions or failures that would have prevented normal operation. Control continuity for both the elevator and rudder was confirmed from the cockpit to the control surfaces.
Weight and balance calculations performed during the investigation estimated the aircraft's gross weight at approximately 7,796.8 lbs. The estimated center of gravity (CG) was calculated to be between 3.2 and 5.6 inches beyond the approved aft limit. The investigation also noted that the cargo loading did not maintain a clear aisle between the crew and passenger compartments, contrary to operating requirements.
Findings
- The aircraft was operated with an aft center of gravity condition of sufficient magnitude that the elevator pitch-down authority could not overcome the pitching moment.
- The application of full landing flaps exacerbated the nose-up pitching moment due to increased downwash on the tail and an aft shift in the center of pressure.
- The pilot failed to accurately determine the actual weight and balance of the aircraft prior to departure.
- The low-speed, left roll, and pitch-down behavior was consistent with an aerodynamic stall.