What happened
On 27 April 1980, flight TG231, an HS-748 Series 11 registered as HS-THB, was performing a multi-leg domestic service through several Thai cities. After completing stops at Udon and Khon Kaen, the aircraft departed Khon Kaen for its final leg to Bangkok International Airport. During the climb, the pilot communicated with Bangkok Area Control Centre, requesting clearance via a specific route and maintaining flight level 120.
As the aircraft approached Bangkok, air traffic controllers issued several descent instructions. At 0642 h, the pilot was cleared to descend to 8,000 ft with an altimeter setting of 1,008 mb. Following a transfer to Bangkok Approach Control, the aircraft was further instructed to descend to 6,000 ft and eventually to 1,500 ft. The pilot confirmed reaching 1,500 ft at 0653 h, and the aircraft was cleared for an ILS approach to runway 21R.
While descending near the airport, the aircraft entered a region of rain and hail. During this period, the aircraft experienced a rapid loss of altitude, causing items in the cabin to fall. Although the aircraft briefly regained its level, a second, more severe loss of altitude occurred approximately thirty seconds later. The aircraft struck a paddy field roughly 8 nautical miles northeast of Bangkok International Airport, skidding about 510 feet before a fire broke out in both wings. There were no survivors listed in the source material.
Findings
Investigations concluded that the pilot flew the aircraft into a thunderstorm that was in an early stage of dissipation. The aircraft was caught in a powerful downdraft while at a low altitude of 1,500 ft, making it impossible to maintain flight. Several contributing factors were identified:
- The crew had not tuned the radio to the ATIS frequency, meaning they missed a special weather report (SPECI) issued four minutes before the accident that warned of nearby thunderstorms.
- The pilot did not utilize the onboard weather radar.
- Although a thunderstorm was visible at higher altitudes, it was not initially in the flight path; however, as the aircraft descended per instructions, the developing storm intercepted the flight path.
- The pilot mistakenly assumed that radar vectors provided by Approach Control would steer the aircraft away from convective activity.