Investigation Summary
The aircraft had arrived from its previous flight at 14:14 and was being prepared for a scheduled departure at 15:15. During this time, the air conditioning packs were running continuously to combat ground temperatures of approximately 35 degrees Celsius. These packs are situated directly beneath the center wing tank, and their operation transferred significant heat to the tank's residual fuel and air mixture, creating a highly flammable environment. At 14:48, approximately 27 minutes before the scheduled departure, the center wing tank exploded. Both CWT fuel pump switches were found in the 'ON' position despite the tank being nearly empty. Investigators found evidence of metal shavings and scoring within the CWT pump housing, suggesting that running the pumps dry created sparks or sufficient heat to ignite the volatile fuel-air mixture.
Final Conclusions
The Aircraft Accident Investigation Committee (AAIC) of Thailand concluded the probable cause was an explosion of the center wing tank resulting from the ignition of a flammable fuel-air mixture. While the exact ignition source could not be determined with absolute certainty, the most likely source was an explosion originating at the center wing tank pump due to running the pump in the presence of metal shavings and a fuel-air mixture. The high ambient temperature and heat from the air conditioning packs contributed to the flammability of the tank's environment.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Center Wing Tank (CWT) Fuel Pumps
Pumps used to move fuel from the center tank to the engines; evidence suggested they were running dry, causing overheating or sparking.
Air Conditioning Packs
Located beneath the CWT, these units generated significant heat during continuous ground operation, increasing the temperature of the fuel vapors.
Fuel Quantity Indication System (FQIS)
Investigated for potential electrical faults or short circuits that could have provided an ignition source, though no definitive link was found.
Interesting Facts
- 01The passenger manifest included Prime Minister Thaksin Shinawatra and his son, leading to early but unfounded rumors of an assassination attempt.
- 02The center wing tank contained only residual fuel, while the wing tanks had been loaded with 5,440 kg of fuel.
- 03Ground temperatures were approximately 35 degrees Celsius (95 degrees Fahrenheit) at the time of the explosion.
- 04Both center wing tank fuel pump switches were found in the 'ON' position in the wreckage.
- 05Metal shavings (steel and aluminum) were discovered specifically within the center wing tank pump canisters and internal pump components.
Safety Actions & Advisories
Fuel Pump Operation Procedures
Reinforcement of procedures to ensure fuel pumps are not operated when tanks are empty to prevent dry-running and potential ignition.
CWT Flammability Reduction
The accident contributed to industry-wide discussions and mandates regarding fuel tank inerting systems and minimizing heat transfer from AC packs to fuel tanks.
Known Controversies & Unanswered Questions
Assassination Theory
Reference ↗Initial reports by Thai officials suggested a bomb might have been used to target Prime Minister Thaksin Shinawatra, but forensic evidence found no traces of high explosives.