What happened
On October 3, 2018, a Bell 206 L4 helicopter, registration VT-PHD, operated by Pawan Hans Limited, was conducting a search and rescue mission in the high-altitude region of Kurgiakh. While returning from a flight near Padum, the pilot observed a group of people walking near a village and decided to land to investigate.
As the helicopter approached the landing site—a terrain feature approximately seven feet higher than the surrounding valley—the pilot initiated a hover. During this phase, the aircraft experienced a sudden, violent yaw to the right. To prevent an uncontrolled spin or toppling, the pilot immediately reduced the collective pitch to bring the aircraft down quickly. While the pilot managed to arrest the rotation, the helicopter struck the edge of a rocky, irregular terrain edge with significant force. The impact caused the tail boom to buckle and the skids to bend, though there were no injuries to the four occupants on board.
The investigation
AAIB India investigators examined the wreckage and the flight conditions at the time of the accident. The investigation focused on the mechanical state of the tail rotor and the aerodynamic performance of the aircraft at a density altitude of approximately 14,000 feet.
Laboratory analysis conducted by the National Aerospace Laboratories (NAL) examined the damaged tail rotor blades. While the pilot initially suggested the aircraft might have been struck by a large fabric-like object, investigators found no evidence of an in-flight object impact. Instead, the damage to the blade tips—specifically the shearing of the material—was consistent with the rotating blades striking hard soil or stone during the heavy landing. The investigation also noted that while a sister aircraft in the fleet was equipped with a high-altitude tail rotor kit, VT-PHD was not.
Findings
- The aircraft was operating at a high density altitude where tail rotor thrust and efficiency were significantly reduced.
- As the pilot reduced airspeed for landing and increased collective pitch to maintain height, the loss of the weathercock effect increased the demand on the tail rotor.
- The tail rotor reached its design limit, triggering Loss of Tail Rotor Effectiveness (LTE).
- The pilot's decision to reduce collective pitch to manage the yaw resulted in a severe heavy landing on uneven ground.
- The tail boom and skids sustained substantial damage due to the impact with the rocky terrain.