Thai Airways International

Thai Airways Flight 311 was conducting the Sierra (VOR/DME) approach to runway 02 at Tribhuvan International Airport, in instrument weather conditions. A flap fault occurred while the flight was on the approach; this caused the crew to ask for clearance back to Calcutta, a decision that was in keeping with both Company and performance requirements, which necessitate the use of full flaps for the steep final approach. Shortly (21 seconds) after making this request, at a distance of approximately 12 nm from the Kathmandu VOR, the flap fault was rectified by retracting and then reselecting the flaps. The crew determined that it was not possible to continue the straight-in approach, due to the steep descent angles required and the position of the aircraft. The crew stated to the control tower that they wished to start their approach again and requested a left turn back to the Romeo fix, which is 41 nm south south-west (202 radial) of the Kathmandu VOR. The Controller, in the non-radar environment, responded by clearing the flight to make the Sierra approach, which starts at the 202 radial and 16 nautical miles from the VOR. The crew response to the clearance was to report that, at the moment, they couldn't land and to ask again for left turn back to Romeo to start their approach again. After further dialogue with the controller, which included requests for a left turn, the crew unilaterally initiated a right turn from the aircraft's 025° heading and commenced a climb from an altitude of 10,500 feet to FL180, when the flight was about 7 nm south of the Kathmandu VOR. The crew reported to the tower controller that the flight was climbing and the controller replied by instructing the crew to report at 16 nm for the Sierra approach. During the turn, there was more discussion between the tower controller and the flight, where it was established that the aircraft was to maintain an altitude of FL115 and was to 'proceed to Romeo' and contact the Area Control Center (ACC) controller. The flight, commencing a descent while in the turn, completed a 360° turn, momentarily rolling out on headings of 045° and 340°, and again proceeded toward the north on a heading of 025° magnetic. When the flight was about 5 nm south-west of the Kathmandu VOR, the crew contacted the ACC and stated that the aircraft was 'heading 025' and they wished to proceed to Romeo to start their approach again; adding they had 'technical problems concerned with the flight.' It was again established that the flight was to proceed to Romeo and the crew agreed to 'report over Romeo.' It was determined from the cockpit voice recorder that the crew was in the process of inserting 'Romeo' and other related navigational information in the Flight Management System, but were experiencing difficulties. The flight continued towards the north on a heading of 025° and then, at about 16 nm north, the heading was altered to the left to 005°. Slightly over one minute later, the Ground Proximity Warning System (GPWS) sounded the warning 'terrain, terrain' followed by 'whoop whoop pull-up'; the aural warning continued until impact approximately 16 seconds later. Engine thrust was increasing and 'Level Change' had been announced on the cockpit, just before the impact occurred at the 11,500-foot level of a 16,000-foot peak; the accident site was located on the 015 radial (north-north east) at 23.3 nm from the Kathmandu VOR. The aircraft was destroyed and all 113 occupants were killed.

After landing, the aircraft was unable to stop within the remaining distance, overran and came to rest. There were no casualties but the aircraft was damaged beyond repair.

Thai Airways Flight 365 was approaching Phuket VOR/DME on radial 119 after a flight from Hat Yai. At the same time Dragon Air Flight 203 (a Boeing 737 registered VR-HYL, carrying 62 occupants) also approached Phuket VOR/DME on radial 090. At 08:34 UTC Dragonair 203 reported at 2500 feet with Thai 365 in sight in front of them. The Thai Boeing was flying at 3000 feet at the time, and was 13 miles from Phuket VOR/DME. Dragonair 203, first priority in approach sequence, then turned right at 12 DME and was going to turn inbound for finals for runway 27. The Thai crew surmised that the other crew were making a false position report to gain landing priority and reported hurriedly that they were at 8 DME inbound and requested visual approach, though they hadn't reached 8 DME yet. This forced Phuket Approach to give Thai 365 landing priority at 08:35. The Dragonair crew (flying IFR) immediately warned that the Thai plane couldn't descend through their flight level. Concentrating on the conflicting traffic the speed decayed to 163 knots until the stick shaker activated. The Thai crew then applied power and raised the landing gear, but the aircraft entered a stall crashed into the sea, disintegrating on impact. All 83 occupants were killed.

Following an uneventful flight from Chiang Mai, the crew initiated the approach to Chiang Rai Airport in good weather conditions. The copilot was the pilot-in-command when the aircraft completed a gear up landing. It slid on runway for about 1,075 meters before coming to rest on the runway. All 43 occupants escaped uninjured while the aircraft was damaged beyond repair.

Following an uneventful flight from Bangkok, the crew started the descent to Phuket Airport by night and good weather conditions. Four minutes after being cleared to descend to 3,000 feet, the pilot reported that he was unable to receive the DME signal. ATC asked the crew if he wanted to conduct a VOR approach to runway 09 but the captain preferred to attempt a visual approach to runway 27. On final, the aircraft struck a hill (800 feet high) and crashed about 18 km short of runway. The aircraft was destroyed and all 11 occupants were killed.

After touchdown at Chiang Rai Airport, the airplane encountered difficulties and was unable to stop within the remaining distance. It overran and came to rest in a ditch. All 21 occupants were evacuated, some of them were injured.

On 27 April 1980, HS-748 Series 11, HS-THB was on a scheduled domestic passenger flight. The flight operated the route Bangkok - Khon Kaen - Udon - Nakhon Phanom - Udon - Khon Kaen - Bangkok. The departure flight was flight number TG221 which departed Bangkok International Airport at 0101 h, arrived Khon Kaen Airport at 0210 h, departed Khon Kaen Airport at 0233 h, arrived Udon Airport at 0251 h, departed Udon Airport at 0309 h, arrived Nakhon Phanom Airport at 0349 h. The return flight, flight number TG231, departed Nakhon Phanom Airport at 0408 h, arrived Udon Airport at 0448 h, departed Udon Airport at 0507 h, arrived Khon Kaen Airport at 0532 h, departed Khon Kaen Airport at 0550 h, ETA Bangkok International Airport at 0656 h. At 0559 h, after take-off from Khon Kaen Airport, the pilot reported to Bangkok Area Control Centre that he was climbing to 6 000 ft, ETA Korat at 0626 h, ETA Bangkok International Airport at 0656 h and requested ATC clearance to Bangkok International Airport via W6 - KT - W1 - BKK. Bangkok Area Control Centre cleared HS-THB to Bangkok International Airport via this route, to maintain FL 120 and asked the pilot to report when the aircraft reached FL 120.
- At 0614 h the pilot reported that HS-THB reached FL 120.
- At 0626 h the pilot reported that the aircraft was over KT.
- AT 0627 h Bangkok Area Control Centre informed the pilot that HS-THB was in radar contact, 5 miles northwest of KT.
- At 0642 h Bangkok Area Control Centre cleared HS-THB to descend to 8 000 ft and informed the pilot that the altimeter setting was 1 008 mb. This was acknowledged by the pilot.
- At 0644 h, Bangkok Area Control Centre advised the pilot to contact Bangkok Approach Control on 119.1 MHz.
- At 0644 h, the pilot contacted Bangkok Approach Control and reported that he was maintaining 8 000 ft. Bangkok Approach Control advised the pilot to descend to 6 000 ft and informed him that the altimeter setting was 1 008 mb. This was acknowledged by the pilot.
- At 0648 h Bangkok Approach Control advised HS-THB to descend to 6 000 ft.
- At 0651 h Bangkok Approach Control advised HS-THB to descend to 1 500 ft.
- At 0653 h the pilot reported that HS-THB had reached 1 500 ft.
- At 0654 h Bangkok Approach Control informed the pilot that HS-THB was 7 miles from the Outer Marker and cleared the aircraft to make an ILS approach to runway 21R. This was acknowledged by the pilot.
- At 0656 h Bangkok Approach Control advised the pilot to contact Bangkok Tower on 118.1 MHz but no answer from the pilot was received. Bangkok Approach Control tried to contact HS-THB until 0709 h but no answer was received. HS-THB operated in good weather conditions on both the outbound and return flights until, descending to runway 21R nearly at the airport, it encountered an area of rain. Later, HS-THB lost altitude rapidly. Many things in the passenger cabin fell to the cabin floor. It was raining with hail. Looking through the windows, some passengers saw grey clouds. Then the aircraft could maintain altitude. Thirty seconds later it again lost altitude, more severely than the first time. Finally it crashed into a paddy field and skidded forward about 510 feet. Fire occurred in both wings for a while. The accident site was 8 NM northeast of Bangkok International Airport.

After touchdown at Kathmandu-Tribhuvan Airport, the four engine airplane was unable to stop within the remaining distance. It overran, lost its undercarriage and one engine before coming to rest in a dump. Onee people on the ground was killed and four passengers were injured. The aircraft was written off.