What happened
During a medical evacuation mission, the helicopter was attempting to land in rough, rocky, and mountainous terrain. The operation took place at a pressure altitude of 9,830 feet. At the time of the accident, the aircraft was operating within a performance-limited portion of its hover performance chart.
While maneuvering for landing in these demanding conditions, the helicopter experienced a loss of tail rotor effectiveness. This mechanical failure resulted in an uncontrolled descent. The aircraft descended rapidly and impacted the rocky ground below.
The investigation
The operational context indicated that the helicopter was operating at the edge of its performance envelope. Being in a performance-limited portion of the hover chart contributed to the inability to maintain control following the loss of tail rotor effectiveness.
Findings
Contributing factors included the high-pressure altitude, the rough terrain, and the operation within a performance-limited zone of the hover chart. The immediate cause was the loss of tail rotor effectiveness.