NTSB Identification: CEN18LA314
On August 3, 2018, about 1530 mountain daylight time, an Airbus EC 130 T2 helicopter, N130TG, lost control while maneuvering near the Dismal River Golf Club, southwest of Mullen, Nebraska. The private pilot was not injured, and the passenger sustained serious injuries. The helicopter sustained substantial damage. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no Federal Aviation Administration (FAA) flight plan had been filed for the flight. The personal flight departed Alliance, Nebraska, about 1430, and was en route to Mullen, Nebraska.
According to the pilot, he was approaching the golf course with the intention of surveying a possible landing site. The pilot reported the weather was clear and breezy with 15 to 20 knots of wind from the southeast. The pilot stated that during the left turn, with an airspeed between 40 and 60 knots, he encountered a loss of tail rotor effectiveness. The pilot stated that he initially added right pedal during the first ½ of the turn and increased it to full right pedal for the remainder of the rotation.
The pilot stated that he accepted responsibility for putting the helicopter into that flight situation and in the future, he needed to perform higher, faster, and wider turns.
According the FAA inspector who responded to the accident, the main rotor and fuselage were substantially damaged during the impact. An examination of the helicopter and its systems revealed no mechanical anomalies that would have precluded normal operations.
The helicopter was equipped with an Appareo Vision 1000 image, audio, and data recorder. The recorder was not damaged and was sent to the National Transportation Safety Board Vehicle Recorders Division in Washington, DC, for examination and data recovery. Parametric data from the accident flight was extracted and is available in the public docket for this accident. The details surrounding the data recovered are contained in the specialist's factual report in the public docket for this investigation. The Appareo Vision 1000 provided a field of view over the pilot's shoulder and forward to the instrument panel, including a partial view outside the helicopter windshield. The flight controls, except for the collective control, were also visible. Only the video events associated with the accident flight were viewed.
The helicopter entered a right turn around a group of buildings. A flagpole visible in the video indicated that the winds were out of the south; the flag was mostly unfurled, and the flag was fully visible. After one right turn, the helicopter started a left turn around the same group of buildings. As the turn begins to tighten in radius the helicopter starts to descend. The ground speed showed a decreasing trend with an indicated airspeed of 30 knots. The heading changed to north, the ground speed decreased, and the airspeed indicator displayed 0 knots. As the helicopter turned to a downwind condition, a left yaw rate rapidly increased and was not arrested, resulting in a loss of yaw control.
At the moment of control loss, the nose was down 18° at which time the pilot made an aft stick input and slight right pedal input, about 1 inch forward of the left pedal. As the yaw continued to develop, the pilot made a left pedal input; this input remained until ground impact. The helicopter rotated 1.25 times from the time of loss of control until ground impact.
According to the FAA Rotorcraft Flying Handbook – Unanticipated yaw is the occurrence of an uncommanded yaw rate that does not subside of its own accord and, which, if not corrected, can result in the loss of helicopter control.
In February 2005, Eurocopter released Service Letter No. 1673-67-04 "Reminder concerning the YAW axis control for all helicopters in some flight conditions" and specifically addressed the operational differences between the Fenestron and the conventional tail rotor. In July 2019, Airbus Helicopters released Safety Information Notice No. 3297-S-00 "Unanticipated left yaw (main rotor rotating clockwise), commonly referred to as LTE" and specifically addressed the characteristics of the unanticipated yaw, and how pilots can respond to avoid or reduce the effect of the unanticipated yaw.