On September 9, 1999, a Robinson R-22-BETA (registration N4076Z) was involved in an aviation accident near Piute, NV. Investigators recorded the probable cause as: the failure of the pilot to maintain rotor rpm while practicing autorotations, resulting in a hard landing and roll over. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
Two flight instructors practicing autorotations experienced a hard landing and rollover after rotor rpm dropped during the final planned maneuver.
Accident Sequence
Two flight instructors were practicing autorotations. The final planned autorotation began at 600 feet above ground level with an airspeed of 70 knots. While turning into the landing area, the pilot maintained rotor rpm in the green arc and airspeed at 60 knots. As he prepared to roll onto final, the low rotor rpm horn sounded and the rotor rpm dropped to 85 percent. The pilot lowered the collective but observed that the descent rate remained high and the rpm did not increase significantly.
A power recovery was attempted, with the other pilot assisting by rolling on the throttle and lowering the collective. At 100 feet, with full throttle applied and the collective lowered, the pilot recognized that a touchdown was imminent and attempted to flare to reduce the descent rate. The rotor rpm remained below 80 percent and airspeed decreased to 40 knots. The pilot raised the collective to cushion the landing, touching down an estimated 200 feet from the intended landing spot. The helicopter landed hard and rolled over onto its right side.