Accident Sequence
According to the investigation, the helicopter began an uncommanded right turn while operating out of ground effect at a forward airspeed of approximately 20 knots. The density altitude at the time was 6,875 feet. The pilot reported that the wind was coming from the helicopter's right front when the turn initiated. The pilot attempted to stop the right turn but was unsuccessful. The helicopter then descended in an uncontrolled manner until it struck a lake.
Pilot Actions and Warnings
The pilot noted that the wind direction relative to the helicopter at the start of the uncommanded turn was from the right front. The pilot's operating handbook (POH) contains warnings about operating at low airspeeds at high altitudes. Specifically, the POH indicates that tailrotor control may be marginal when the relative wind is in the critical wind azimuth area, which begins at the right front of the helicopter. The investigation found no reports of any preexisting mechanical failures or malfunctions that could have contributed to the loss of control. Additionally, it was determined that the pilot did not evaluate the helicopter's performance data before departing.
Environmental Conditions
The accident sequence unfolded while the helicopter was flying out of ground effect. The density altitude was 6,875 feet, and the forward airspeed was about 20 knots. The wind originated from the right front of the helicopter, a direction identified in the POH as potentially problematic for tailrotor effectiveness.
Investigative Findings
Investigators concluded that there were no prior mechanical issues with the helicopter. The examination revealed no evidence of a preexisting failure or malfunction that would explain the loss of control. The pilot's failure to review performance data before the flight was noted as a contributing factor.