What happened
Following departure from the airport, the helicopter turned north and climbed to an altitude reported to be between 100 and 800 feet above ground level. As the aircraft approached the accident site, witnesses observed the tail lowering and the aircraft slowing its speed while turning slightly to the east. This was followed by a rapid descent toward the terrain.
Witnesses noted that near the start of this descent, the main rotor blades either slowed their rotation significantly or stopped turning entirely. One witness reported that almost immediately after observing the change in the rotation speed of the main rotor blades, the aircraft dropped out of the sky.
The investigation
Examination of the wreckage provided evidence of coning of the main rotor blades. Investigators found no evidence of any flight control malfunction or a loss of engine power.