What happened
During a local instructional flight, a helicopter impacted the ground with a high rate of descent. Prior to the accident, a witness located on a farm approximately 3 miles from the site observed and heard the aircraft performing maneuvers consistent with multiple practice autorotations to a power recovery. Following these maneuvers, the helicopter flew toward the airport.
Witnesses near the accident site observed the aircraft in level, controlled flight at approximately 500 feet above ground level, also traveling toward the airport. These witnesses noted that the helicopter's nose dropped, after which it dove toward the ground and disappeared behind a tree line. During this period, witnesses reported hearing normal sounds coming from the engine.
The investigation
The wreckage and ground scars indicated that the aircraft collided with the ground at a high rate of descent while in a level, upright attitude, subsequently rolling onto its right side. Examination of the main rotor blades showed evidence that they had flexed downward and sliced into the tail boom at a high rotational rate and a driven energy state.
Investigation of the drive train provided evidence consistent with engine rotation and power production. Furthermore, an inspection of the airframe and engine revealed no preimpact anomalies that would have prevented the normal operation or functionality of the control system.