Cahokia/St. Louis, IL, USA
N931SH
ROBINSON HELICOPTER R22
Same as Factual Information
According to the flight instructor, he was instructing his student in hovering flight operations. He reported that he instructed the student to execute a right pedal turn at a three foot hover. The instructor recalled that the student complied and during the turn, as the tail came into the wind, the helicopter started to weathervane, and the turn rate increased rapidly and did not subside until the helicopter impacted the ground. The helicopter sustained substantial damage to the fuselage and both rotor systems. The instructor reported that there were no mechanical anomalies or malfunctions with any portion of the helicopter that would prevent normal flight operations. The instructor reported that the wind velocity at the time of the accident was 11 knots gusting to 16 knots. Weathercock stability is defined as a region of loss of tail rotor effectiveness (120 degree - 240 degree tailwind) that will weathervane the helicopter, and if not prevented will result in a loss of helicopter control about the horizontal axis. According to the Helicopter Flying Handbook (FAA 8083-21A): Pilots who put themselves in situations where the combinations above occur should know that they are likely to encounter LTE. The key is to not put the helicopter in a compromising condition but if it does happen being educated enough to recognize the onset of LTE and be prepared to quickly react to it before the helicopter cannot be controlled.
The flight instructor's delayed remedial action and his failure to remain vigilant as the helicopter entered the weathercock stability region, in gusting wind conditions, resulting in loss of tail rotor effectiveness and ground impact.
Source: NTSB Aviation Accident Database
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