Accident Overview
A helicopter flight instructor reported that a commercial pilot rated/helicopter flight instructor candidate was practicing autorotations with power recovery to the runway. During a practice 180-degree autorotation, the flight instructor candidate executed the landing flare too low to the ground, resulting in a tail rotor strike.
Pilot Actions
The flight instructor further reported that after the tail rotor strike, the helicopter yawed un-commanded to the right approximately 180 degrees, at which point he took control of the controls and landed the helicopter.
Aircraft Damage
The helicopter sustained substantial damage to the vertical stabilizer and tail rotor drive assembly.
Mechanical Assessment
The flight instructor reported that there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation.
Relevant Guidance
The FAA Helicopter Flying Handbook FAA-H-8083-21A (2012) discusses procedures for autorotation and states in part: "Care must be taken in the execution of the flare so that the cyclic control is neither moved rearward so abruptly that it causes the helicopter to climb nor moved so slowly that it does not arrest the descent, which may allow the helicopter to settle so rapidly that the tail rotor strikes the ground… extreme caution should be used to avoid an excessive nose high and tail low attitude below 10 feet. The helicopter must be close to the landing attitude to keep the tail rotor from contacting the surface."