Investigation Summary
The flight was a non-scheduled charter engaged by the Government of Arunachal Pradesh to transport officials and tourists. The approach to Tawang, located at an altitude of approximately 11,000 feet, was conducted in challenging terrain. As the helicopter neared the helipad, it undershot the landing zone by approximately 27 meters and was roughly one meter below the helipad's surface level. The forward momentum combined with a slow rate of descent led to the left oleo leg shearing off upon impact with the helipad's edge. In an attempt to recover, the crew increased the collective to 13.8 degrees to boost rotor thrust. However, the existing left bank and the sudden increase in thrust created an uncontrollable angular momentum, causing the bank angle to snap from 5 degrees to 85 degrees in just one second. The main rotors struck the helipad surface and shattered, after which the airframe slid down the adjacent steep slope and overturned.
Final Conclusions
The DGCA India investigation concluded the direct cause was the helicopter undershooting the helipad and sinking below its height during the final approach. Contributory factors included the crew's disregard for local QNH (atmospheric pressure) and temperature data provided by Tawang Control, and the fact that the All Up Weight (AUW) exceeded the limits stipulated in the Flight Manual for Category A operations. While initial reports confirmed 17 fatalities at the scene, the final toll reached 19 as two survivors later succumbed to their injuries.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Main Rotor System
The rotors shattered upon impacting the helipad surface after the aircraft reached an 85-degree bank angle.
Left Oleo Leg
The left landing gear strut sheared off when it struck the concrete edge of the helipad during the undershoot.
Collective Pitch Control
The crew increased collective to 13.8 degrees during the impact sequence, which inadvertently increased angular momentum and worsened the roll.
Interesting Facts
- 01The helicopter was carrying 23 people, consisting of 19 passengers and 4 crew members.
- 02The Tawang Civil Helipad is situated on a hilltop at an altitude of approximately 11,000 feet.
- 03The aircraft involved, VT-PHF (MSN 356C06), was manufactured in 1996.
- 04The aircraft had previously been involved in an emergency landing in the same region on August 6, 2010.
- 05The investigation found the helicopter's weight was above the limit for Category A operations.
- 06The initial death toll was 17; two passengers initially survived but later died of their injuries, bringing the final toll to 19.
- 07An Aircraft Maintenance Engineer (AME) was among the 19 passengers on board.
Safety Actions & Advisories
Weight and Balance Oversight
The investigation highlighted the necessity of adhering to Category A weight limits for high-altitude operations.
Meteorological Compliance
Recommendations were made for aircrew to strictly utilize local QNH and temperature data provided by local controllers rather than relying on estimates.