Introduction
A flight intended for a helicopter-rated instructor pilot to become familiar with the accident make and model involved an autorotation demonstration on takeoff at low altitude. The flight instructor giving instruction planned to demonstrate the maneuver with the student following along on the controls.
Sequence of Events
After ascending to about 150 feet and reaching an airspeed of about 50 knots, the instructor explained to the student that he would lower the collective without adding cyclic to maintain airspeed. The instructor reported lowering the collective and feeling the student on the collective. He then applied right pedal, splitting the needles. Subsequently, he felt the student pull back on the cyclic and pull up on the collective. The instructor stated, “I said ‘…no, push down,’ and I forced the cyclic forward.”
The rotor RPM had decayed outside normal parameters. The instructor noted that the student kept pulling up on the collective. He tried to roll on power and force the cyclic forward, but the helicopter was descending too fast. The student stated that during the demonstration, he looked down at the rotor RPM and noticed it was about 320 RPM, and it remained that low as the helicopter approached the ground. The student repeatedly told the instructor "low RPM" at least five times.
After the hard landing, the instructor told the student that he had grabbed the controls because the helicopter didn’t pitch forward as intended. The student denied touching any controls and suggested that the lack of control was likely due to the low rotor RPM.
Post-Accident Examination
An examination of the airframe by a Federal Aviation Administration inspector revealed no pre-impact anomalies. Neither pilot reported any malfunction of the airframe or engine.
Probable Cause
The source does not provide a stated probable cause.