Boeing 737-400 “Narathiwat” was parked at gate 62 at the domestic terminal of Bangkok Airport and was being prepared by 5 cabin crew members and 3 ground staff members for a flight to Chiang Mai (TG 114). Ground temperatures were in the high 35 degree Celsius and the air conditioning packs, which are located directly beneath the center wing tank and generate heat when they are operating, had been running continuously since the airplane’s previous flight, including about 40 minutes on the ground. At 14:48, some 27 minutes before scheduled departure time, fuel vapours in the center wing tank probably ignited, causing an explosion. A fire erupted in the cabin, killing a flight attendant and injuring 6 others. Eighteen minutes later, the fire caused the right wing tank to explode. The fire was put out in an hour, but by then the aircraft had been gutted by the fire. PROBABLE CAUSE: “An explosion of the center wing tank resulting from ignition of the flammable fuel/air mixture in the tank. The source of the ignition energy for the explosion could not be determined with certainty, but the most likely source was an explosion originating at the center wing tank pump as a result of running the pump in the presence of metal shavings and a fuel/air mixture.”