Incident Details
During an approach to landing, while descending through approximately 100 feet above ground at an airspeed of 60 knots, the pilot heard a loud bang. He immediately entered an autorotation. However, during the flare just before touchdown, the rotor RPM was insufficient, leading to a hard impact. As the helicopter struck the ground, the main rotor blades cut through the tailboom, severing it. The pilot noted that at that moment, the Rolls Royce (Allison) 250-C20B engine began spooling up.
Pilot Observations
The pilot stated that no audible engine-out alert sounded during the entire sequence. Furthermore, the helicopter was not equipped with an auto-relight system.
Post-Accident Testing
A test run of the engine conducted after the accident showed no abnormalities. According to the height-velocity diagram for this helicopter model, a successful autorotation could be accomplished from an elevation of 100 feet for airspeeds of 41 knots and above.