What happened
During an approach to a private runway consisting of dirt and gravel, the crew of a STOL cargo airplane was attempting to land with 40 degrees of flaps configured. As the aircraft descended, the flight crew noted fluctuations in both ground speed and indicated airspeed, signaling the presence of windshear. Approximately 100 to 200 feet above the surface, the aircraft encountered a downdraft that caused it to drift right of the runway centerline.
In an attempt to recover, the pilot increased engine power and applied full rudder and left aileron; however, the aircraft could not be stabilized in terms of pitch or direction. The right wing of the aircraft made contact with trees located before the runway threshold, which intensified the rightward yaw. As the aircraft approached the ground, the pilot moved the throttles to the idle position. The aircraft impacted the ground on the right main landing gear and the right forward section of the fuselage, subsequently pivoting 180 degrees from its original approach heading. There were 0 fatalities and 0 injuries reported in the accident.
Findings
Investigation into the local environment suggested that easterly winds, which were blowing at approximately 15 knots at the time, are known to generate downdrafts near runway 05. Furthermore, the aircraft's operational characteristics make it highly sensitive to windshear and gusts as low as 5 knots when flying at low speeds. Company documentation specifies that maintaining level wings in such conditions may require significant aileron input and that pilots should increase threshold airspeed by half the gust factor during gusty conditions to maintain stability.