Accident Sequence
The captain and first officer were landing a short takeoff and landing (STOL) cargo airplane on a private, dirt and gravel surface runway. The airplane was configured for landing with 40 degrees of flaps. During the landing approach, variations in indicated airspeed and ground speed indicated windshear conditions. About 100 to 200 feet above the ground, the airplane encountered a downdraft and began to drift to the right of the runway centerline. The captain reported increasing engine power and applying full left aileron and rudder, but could not gain directional or pitch control. The right wing struck trees short of the runway threshold, increasing the airplane's right yaw. As the airplane neared the ground, the captain pulled the engine throttles off. The airplane struck the ground with the right main landing gear and right front portion of the fuselage, then pivoted to the right, 180 degrees from the approach heading.
Weather Conditions
The airport owner reported that wind from the east may produce downdrafts in the area of runway 05. At the time of the accident, the wind was blowing from the east at about 15 knots.
Pilot Reports
The first officer reported that the captain appeared to be attempting to maintain a stabilized approach angle by varying the pitch attitude of the airplane.
Company Training
A review of company training literature indicated that the airplane is especially sensitive to slight wind shear, with wind gusts as low as 5 knots affecting control when operating at low airspeeds. Pilots were cautioned that when flying at low speeds, large aileron application may be required to maintain wings level. During gusty wind conditions, the threshold airspeed should be increased by one-half the gust factor, and any lateral displacement corrected rapidly. If a wing drops beyond corrective action of full aileron, power should be increased immediately to regain level flight.
Probable Cause
The official probable cause was the captain's failure to maintain the proper glidepath, and improper short field landing procedures. Factors in the accident were a downdraft, and the captain's inadequate evaluation of the weather conditions.