Incident Overview
A certified flight instructor (CFI) and a student pilot, who held a foreign-issued fixed-wing certificate, were conducting a local training flight. The purpose of the flight was, in part, to practice autorotations.
Autorotation Demonstration
The CFI first demonstrated an autorotation. She announced "…entering autorotation in 3-2-1" and lowered the collective while simultaneously adding right pedal for trim. Once the collective was fully down, she closed the throttle. The CFI began recovery at approximately 1,000 feet by cracking open the throttle and allowing the governor to take over after 80 percent revolutions per minute (RPM).
Student Practice
After the demonstration, the CFI reviewed the recovery procedure with the student. She remained on the controls while the student performed the control applications. The student successfully completed one autorotation.
Second Autorotation and Recovery Attempt
For the second autorotation, the student entered the maneuver and at 1,000 feet above ground level, the CFI requested a recovery. The student rolled on the throttle, and the CFI felt a yaw to the right. She countered with left pedal and stated "I have the controls." The student relinquished all controls.
Unexpected RPM Behavior
The CFI observed that the engine and rotor RPMs were excessively high. She reduced throttle to lower engine RPMs. She then raised the collective to reduce rotor RPM, but neither RPM needle decreased. The helicopter maintained a level attitude but descended toward the ground.
Landing and Tail Separation
As the helicopter neared the ground, the CFI searched for a landing area. During the landing, the low rotor RPM horn sounded, and the helicopter touched down. After exiting, the crew saw that the tail boom had separated from the helicopter.
The CFI reported no preimpact mechanical malfunctions or failures with the helicopter that would have precluded normal operation.