Incident Overview
A flight instructor and a commercial pilot were conducting training for the pilot's upcoming flight instructor practical test. The instructor asked the pilot to demonstrate a simulated engine failure with autorotation to landing. The pilot reduced power and entered an autorotation. Airspeed was maintained between 65 and 70 knots, rotor rpm between 98 and 100 percent.
Sequence of Events
The rate of descent was 2,000 feet per minute (fpm) during a 180-degree turn. After aligning with the runway, the rate decreased to 1,800 fpm. Rotor rpm dropped to 97 percent and continued to decrease. At 100 feet above ground level (agl), the low rpm warning horn and light activated, with rpm at 94 percent.
The instructor took control of the helicopter, applied full power, and executed a small cyclic flare while lowering the collective slightly to recover rpm. The helicopter began to shake with a low-frequency vibration, and rpm remained between 92 and 94 percent. At approximately 50 feet agl, the instructor applied a strong cyclic flare to reduce the rate of descent. The vibrations persisted, and the helicopter continued to settle.
Just before ground contact, the instructor noted the rpm needles were "married at 92 percent." The helicopter contacted the runway tail first, followed by the rear portion of the skids. The helicopter bounced and began to spin. It came to rest upright with the engine still running.