Investigation Summary
Flight 409 was the crew's fifth flight of the day to Lukla. Despite reports of deteriorating weather and ground fog, the crew elected to continue the visual approach. During the final phase, the aircraft deviated 15 degrees to the right and descended to 8,500 feet, which was below the runway threshold elevation of approximately 8,900 feet. The First Officer issued two warnings regarding the low altitude, but the Captain did not immediately respond. When the crew realized they were too low, they attempted an immediate climb while in a landing configuration (full flaps and gear down). This maneuver created excessive drag and a high angle of attack, leading to a stall. A continuous stall warning sounded for 13 seconds until impact. The aircraft struck a tree 180 feet short of the threshold and then the ravine slope 100 feet short of the runway before sliding 200 meters down. The investigation also noted that Lukla Tower failed to close the airport despite visibility falling below standard operating procedures.
Final Conclusions
The Civil Aviation Authority of Nepal concluded that the probable cause was an aircraft stall resulting from excessive drag and a sudden increase in angle of attack at low speed. This occurred during an attempt to initiate an immediate climb in a landing configuration. Contributing factors included critical terrain, rapidly deteriorating weather, the pilot's loss of situational awareness, improper response to the stall warning, and violations of standard operating procedures by both the crew and air traffic services.
Video Analysis
Summit Air 409 | Mini Air Crash Investigation — A Let L-410 cargo flight crashes short of the runway at the world's most dangerous airport in Lukla, Nepal, due to low visibility and pilot error.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
48 years old; died shortly after rescue.
First Officer
27 years old; died in intensive care.
Systems & Failure Modes
Stall Warning System
The system provided two short warnings followed by a 13-second continuous tone, but the crew failed to advance power levers to maximum to recover.
Landing Configuration
The deployment of full flaps and landing gear created significant drag, which prevented the aircraft from climbing effectively when the pilot increased the angle of attack.
Interesting Facts
- 01The aircraft was a Let L-410UVP-E20 built in 2014.
- 02The Captain had over 9,000 total flight hours, with 1,900 hours on the L-410.
- 03The airport lacked navigational equipment, requiring a purely visual approach.
- 04The aircraft was in a full landing configuration (flaps and gear down) when the stall occurred.
- 05The investigation suggested the crew may have been stressed and fatigued.
- 06The aircraft (9N-AKY) was involved in a prior minor accident on June 2, 2015, when it landed at Pokhara with the nose gear retracted.
Safety Actions & Advisories
Runway Extension Recommendation
The investigation committee suggested considering a runway extension at Lukla Airport to increase the safety margin for landing aircraft.
SOP Enforcement
The report emphasized the need for Air Traffic Services to strictly follow SOPs regarding airport closure during deteriorating weather conditions.