Incident Overview
During a flight review, a pilot who was also a certified helicopter flight instructor was demonstrating a 180-degree autorotation to another flight instructor. The maneuver was conducted as part of the review.
Sequence of Events
On final glide at approximately 100 feet above ground level (agl), the landing checks were completed: rotor RPM was within the green arc, airspeed was 60 knots, and the landing skids were aligned with the runway. At about 60 feet agl, the rotor RPM had decreased to the bottom of the green arc. The flight instructor expected the pilot to initiate a flare, but the flare was described as "very mild, if none, with little reduction in aircraft speed and rate of descent." Subsequently, the flight instructor "hesitated" in taking control of the helicopter. The helicopter then landed hard and skidded down the runway.
Damage and Examination
During the hard landing, the main rotor blades severed the tail boom. An examination of the airframe found no anomalies that would have precluded normal operations.
Conclusion
The investigation did not specify a probable cause for the hard landing.