What happened
A flight instructor and a student were performing straight-in autorotations with power recoveries in a helicopter. During the first four attempts of the training session, the student acted as the primary manipulator of the controls. Because the student was initiating the flare at too high an altitude, the instructor instructed that they perform the next approach together, with both individuals maintaining control of the aircraft.
During the flare phase of this subsequent autorotation, the stinger of the aircraft struck the runway surface. Following this impact, the tail rotor also contacted the ground, causing the helicopter to yaw 360 degrees to the right. The aircraft came to a stop approximately 100 feet from the initial point of contact. The force of the impact caused the main rotor to sever the tail boom.
Findings
The instructor reported that the student misinterpreted the instructions for the shared control maneuver. While the instructor intended for the student to initiate the flare with the instructor merely following through to guide a lower flare height, the student believed the instructor would be making the primary control inputs.
Safety message
The flight instructor noted that this accident could have been prevented through better communication between the student and instructor regarding which individual is responsible for initiating control inputs during all phases of flight, particularly during critical phases.