The flight instructor's improper supervision of the dual student during a practice autorotation landing by allowing an excessive aft pitch attitude and low main rotor rpm conditions to develop during the landing/flare touchdown, which resulted in the helicopter making a hard landing on the heels of the skids, and the main rotor severing the tail boom.

The pilot-in-command's improper aft application of cyclic control during a simulated touchdown autorotation on landing flare touchdown, resulting in the main rotor blades colliding with the tail boom assembly. Contributing to the accident was the improper supervision of the pilot-in-command by the check pilot.