Incident Overview
While operating under Instrument Flight Rules (IFR) at an altitude of 10,000 feet over mountainous terrain, a helicopter experienced violent vertical vibrations. These vibrations persisted for approximately five minutes until the helicopter crash-landed. The onboard weather radar was used to navigate around mountain tops that were obscured by clouds.
Final Descent and Impact
At an altitude of about 200 feet above ground level, the helicopter caught fire. Subsequently, tail rotor control was lost, both engines quit, and cyclic control became unresponsive. The helicopter was destroyed by post-crash fire.
Preceding Inspection
Approximately one hour of flight time before the incident, the helicopter had undergone an inspection during which the main rotor flight control system bolts were retorqued. Examination of the wreckage revealed that all but one of these bolts were recovered. The rod end for the missing bolt was also found.