Thai Airways International Flight 311

Thai Airways International Flight 311 (TG311/THA311) was a scheduled flight from Bangkok, Thailand's Don Mueang International Airport to Kathmandu, Nepal's Tribhuvan International Airport. On 31 July 1992, at 07:00:26 UTC (12:45:26 NST; 14:00:26 ICT), the Airbus A310 operating the route crashed into the side of a mountain 37 km north of Kathmandu, killing all 113 passengers and crew members on board. This was both the first hull loss and the first fatal accident involving the Airbus A310.

Accident

Flight 311 departed Bangkok at 10:30 local time (03:30 UTC). It was scheduled to arrive in Kathmandu at 12:55 Nepal Standard Time (07:10 UTC). After crossing into Nepalese airspace, the pilots contacted air traffic control (ATC) and were cleared for an instrument approach from the south called the "Sierra VOR circling approach" for Runway 20. Nepalese ATC at the time was not equipped with radar. The captain was evidently uncomfortable with this approach, as he did not want to fly so near to the higher northern mountain range and turn around in poor visibility.

Shortly after reporting the Sierra fix 10 km south of the Kathmandu VOR, the aircraft called ATC asking for a diversion to Calcutta, India, because of a "technical problem" (while attempting to extend the flaps, they had become stuck, making the steep descent into Kathmandu unsafe). Before ATC could reply, the flight rescinded their previous transmission; they retracted and re-extended the flaps properly. The flight was then cleared for a straight-in Sierra approach to Runway 02 and told to report leaving 9500 ft. The captain asked numerous times for the winds and visibility at the airport, but ATC merely told him that Runway 02 was available.

The captain asked four times for permission to turn left, but after receiving no firm reply to his requests, he announced that he was turning right and climbed the aircraft to flight level 200, intending to turn back to point Romeo and re-attempt the straight-in approach. The controller handling Flight 311 assumed from the flight's transmissions that the aircraft had called off the approach and was turning to the south, so he cleared the aircraft to 11500 ft, an altitude that would have been safe in the area south of the airport. The flight descended back to 11,500 ft, unintentionally went through a nearly 360° turn (rather than a 180-degree one to return to southern point Romeo), and passed over the airport northbound.

Seconds before impact, the ground proximity warning system (GPWS) activated, and sounded alarms warning the crew of the imminent collision with the mountains. First Officer Boonyayej warned Captain Suttimai and urged him to turn the aircraft around, but possibly due to his frustration from the communications with ATC, Suttimai erroneously stated the GPWS was just giving false reports. The aircraft crashed into a steep rock face in a remote area of the Langtang National Park at an altitude of 11500 ft and with a ground speed of 300 kn, killing all 113 people on board.