Accident Overview
A flight instructor and a new student were on an introductory flight when witnesses observed the helicopter in apparently normal flight. They then heard a loud bang and saw the helicopter abruptly pitch nose-down while the main rotor blades detached. One witness noted a turn and climb moments before the accident; two others reported level cruise flight just prior.
Weather and Visibility
At the time of the accident, the sky was clear, visibility was at least 10 miles, and a light breeze was present. No other aircraft were in the immediate vicinity.
Wreckage Distribution
The main wreckage came to rest in an open dirt field. Plexiglas fragments and left door components were found about 400 feet from the main wreckage. Additional items, including sunglasses, a left skid tube-mounted component, and the main rotor blade assembly, were scattered 140 to 330 feet from the main wreckage.
Rotor Hub Examination
Examination of the rotor hub revealed cracked teetering stops and broken droop stop tusks on both rotor blade spindles. The physical evidence indicated that the main rotor deviated from its normal plane of rotation, resulting in mast bumping, contact between the main rotor blades and the fuselage, and separation of the main rotor assembly.
Mechanical Assessment
No evidence of any preimpact mechanical malfunction was found with the helicopter. The initiating event that led to the main rotor divergence could not be determined.