What happened
In the period leading up to the accident, several issues involving the horizontal stabilizers and the pitch-trim system had been identified and documented. Maintenance efforts were carried out by personnel from the Royal Thai Air Force; however, these repairs were reportedly not performed in accordance with the official procedures provided by Boeing. To address these technical concerns, a Boeing engineer was sent to Thailand to perform necessary inspections and functional tests.
During the final approach to Muang Khon Kaen Airport, the Boeing aircraft experienced significant longitudinal instability, characterized by alternating pitch-up and pitch-down movements, which eventually led to a stall. The crew attempted to recover by increasing engine thrust, which briefly stabilized the aircraft. However, a second stall occurred shortly thereafter. In an effort to manage the descent rate and regain stability, the crew lost control of the aircraft. The plane entered an uncontrolled descent and impacted a rice paddy field a few kilometers from the airport. The impact resulted in the destruction of the aircraft, registration HS-TGQ (also identified by the military registration 33-333), and six fatalities.
Findings
- Maintenance performed on the pitch-trim system and horizontal stabilizers by Royal Thai Air Force technicians did not follow Boeing-mandated repair procedures.