Investigation Summary
During the approach to Kathmandu, the crew experienced a technical fault with the inboard flaps. While attempting to resolve the issue and communicating with a controller who had limited English proficiency and radar capability, the captain became frustrated. The crew requested a diversion to Calcutta but then decided to attempt the approach again. During a series of turns intended to reposition the aircraft, the crew inadvertently maintained a northerly heading toward high terrain instead of the intended southerly heading. The Ground Proximity Warning System (GPWS) sounded, but the crew dismissed it as a false alarm until seconds before impact at 11,500 feet.
Final Conclusions
The investigation concluded the primary cause was the crew's failure to follow established approach procedures and maintain situational awareness. Contributing factors included ineffective communication between the crew and ATC, the controller's failure to alert the crew of their incorrect heading, and the crew's preoccupation with a minor mechanical flap malfunction.
Video Analysis
The Kathmandu Disaster | Thai Airways Flight 311 — An analysis of the 1992 crash of Thai Airways Flight 311 into the Himalayas due to navigational errors and communication breakdowns.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
GPWS
Ground Proximity Warning System; provided alerts that were ignored by the crew.
Inboard Flaps
A mechanical fault in the flap system initially distracted the crew from navigation.
FMS
Flight Management System; the crew failed to properly program or monitor the heading during the missed approach.
Interesting Facts
- 01The aircraft was only 5 years old at the time of the accident.
- 02Kathmandu Airport lacked primary radar at the time of the crash.
- 03The crash site was located approximately 37 miles north of Kathmandu.
- 04All 99 passengers and 14 crew members perished in the impact.
- 05The investigation was hampered by the extremely rugged terrain and monsoon weather.
Safety Actions & Advisories
Radar Installation
Following the crash and the subsequent PIA 268 disaster, modern radar systems were installed at Kathmandu.
CRM Training
Thai Airways enhanced Crew Resource Management training to address captain-centric authority issues and communication.