Accident Details
During takeoff, prior to transitioning to forward flight, the helicopter rolled violently to the right one complete revolution, impacting the ground inverted and then coming to rest upright on its skids. Six witnesses and the pilot reported the helicopter was hovering at between 2 and 5 feet above the ground before the roll ensued.
Injuries
A passenger in the left front seat, restrained by a lap belt and partially restrained by a shoulder belt that separated under load, was struck on the helmet and left shoulder by a main rotor blade that swept along the left side of the helicopter and was seriously injured. A passenger in the left rear seat, with a lap belt but without a shoulder restraint available, was partially ejected from the helicopter and was struck by the passing main rotor blade and fatally injured.
Wind Conditions
In the 2-hour period before the accident, a thunderstorm passed west of the accident location and there was a windstorm at the accident location estimated to have been 50 - 60 knots. The main and tail rotor blades were secured during the windstorm. At the time of the accident, the wind was steady on the nose of the helicopter at 5 - 10 knots. None of the witnesses reported observing any dust devils or unsteady wind.
Investigation
The ground surface near the initial hover location, where marks may have been present, was obscured by emergency vehicle movement and rain that fell after the accident and prior to the investigator's arrival on-scene. The investigation and laboratory examination of fracture surfaces did not reveal any evidence of preaccident mechanical failures.