What happened
During an aeromedical evacuation (EMS-MEDEVAC) flight conducted at night over mountainous terrain, the pilot interrupted a normal position report to broadcast "MAYDAY" three times. While the pilot provided his position to a company dispatcher, he did not state the nature of the emergency. No further communications were recorded following the distress calls.
Witnesses traveling in a southbound automobile observed the helicopter flying toward them from the south. According to these witnesses, the fuselage of the aircraft began rotating in a counter-clockwise direction. The helicopter then veered toward the west, moved out of sight, and crashed.
The investigation
Investigators located all major components of the aircraft, with the exception of approximately 33 inches of the tail rotor drive shaft and its #5 bearing. The tail boom was recovered in three separate sections.
Examination of the wreckage revealed rotational and longitudinal scoring damage on the tail boom near the #3 and #5 bearing supports. A laboratory report determined that this rotational damage occurred prior to the gross deformation of the tail boom and the subsequent in-flight breakup of the helicopter.