Accident Overview
A helicopter accident occurred when a private pilot lost directional control shortly after takeoff. The pilot, who had accumulated 597 hours of flight time, was departing on his third flight of the day in a northerly direction. Immediately after liftoff, the helicopter began to spin to the right, and the low rotor rpm warning sounded. The pilot reported applying left rudder pedal input, but it had no effect.
Autorotation and Ground Impact
At approximately 20 feet above ground level, the pilot entered an autorotation maneuver. During the descent, the pilot stated that he flared excessively, causing the tail boom to strike the ground. After the rotor system stopped, the pilot and three passengers exited the helicopter without further incident.
Contributing Conditions
The FAA Rotorcraft Flying Handbook (FAA-H-8083-21) notes that under conditions of high weight, high temperature, or high density altitude, rotor rpm may remain low even with maximum throttle. The handbook further explains that because the tail rotor is geared to the main rotor, low main rotor rpm can reduce tail rotor thrust, potentially leading to a loss of directional control. According to the NTSB Investigator in Charge, the density altitude at the time of the accident was calculated to be 2,033 feet, and the takeoff weight was within 100 pounds of the helicopter's maximum certified weight. The investigation found no mechanical deficiencies prior to the accident.