N74914Hughes TH-55 · 1968

According to the student pilot, he had completed a solo flight earlier in the day that included 7 takeoffs and landings. After refueling, he completed a local flight and returned to the departure airport where he initiated an approach to the runway with a 7-knot, left quartering tailwind. The approach terminated "perfectly" to a normal hover. According to the pilot, the helicopter "started spinning to the right" and the spin could not be arrested with full application of left pedal. The pilot stated he then increased collective pitch and the corresponding increase in engine power aggravated the spin. He then attempted a hovering autorotation, but the helicopter landed hard, rolled over on to its side, and was substantially damaged. A witness described the helicopter as it approached "flying somewhat erratically" about 40 feet above the runway. The helicopter was "twisting" to the left and right as it hovered "shakily" closer to the runway. The helicopter noise increased, the nose pitched up, the main rotors struck the ground, and the helicopter came to rest on its side. An FAA advisory circular stated that loss of tail rotor effectiveness (LTE) was a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, could result in the loss of aircraft control. Further, any maneuver which required the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind created an environment where unanticipated right yaw may occur. The pilot reported 40 total hours of flight experience, all of which was in the accident helicopter make and model. A detailed examination of the wreckage by Federal Aviation Administration inspectors revealed no pre-impact mechanical anomalies.