What happened
During the landing phase of the flight, the pilot applied aft cyclic input immediately before touchdown. This maneuver created a tail-low attitude for the aircraft. While the tail stinger is designed to contact the ground first to prevent such incidents, the terrain behind the concrete landing pad sloped downward. Because the stinger was positioned over this sloping ground, the tail rotor made contact with the earth and detached from the aircraft.
Following the separation of the tail rotor and the gearbox, the helicopter experienced a rapid rightward yaw of 360 degrees, driven by the torque from the active main rotor. As the pilot lowered the collective, the rate of yaw had not been sufficiently reduced by rolling off the throttle. This continued rotation caused the helicopter to roll over upon the skids making contact with the ground, ultimately leading to the main rotor blades striking the surface.
The investigation
Investigators examined the sequence of events leading to the ground contact and the physical state of the aircraft. The investigation focused on the interaction between the aircraft's attitude and the specific topography of the landing site. It was determined that the downward slope of the ground away from the helipad prevented the tail stinger from acting as a buffer, allowing the tail rotor to strike the ground directly.