Background
In the days leading up to the accident, multiple problems with the pitch-trim system and the horizontal stabilizers were reported by the crew. Technicians from the Royal Thai Air Force performed repairs, but these were not carried out in accordance with Boeing’s published procedures. Consequently, a Boeing engineer was dispatched to Thailand to conduct further controls and tests on the aircraft.
Accident
During the approach to Muang Khon Kaen Airport, the aircraft began to pitch up and down, then entered a stall. The crew increased engine power and briefly regained control. However, a second stall occurred shortly thereafter. The crew attempted to recover and reduce the rate of descent, but the aircraft entered an uncontrolled descent and crashed in a rice paddy field located a few kilometers from the airport. The aircraft was destroyed, and all six occupants were killed. The aircraft carried the dual registration 33-333 (military) and HS-TGQ (civil).
Investigation
The official investigation concluded that the loss of control occurred when the crew retracted the flaps and increased engine power, likely following a technical problem with the pitch-trim control system. However, investigators were unable to determine the exact cause of the pitch control system malfunction.