Bell 206B III N43MA accident near Missoula, Montana

Probable cause

A dynamic rollover during attempted liftoff.

NTSB analysis

The fixed base and helicopter operator was conducting an evaluation of a prospective pilot-employee for the company. The prospective employee had obtained most of her flight experience in a helicopter model that was different from the single-rotor helicopter being used for the evaluation. On the day of the accident, after a brief flight with another company pilot, the prospective employee landed the helicopter and remained in the right seat, while the other pilot exited, and the company chief pilot took the left seat. The prospective employee then flew the helicopter to another location. The approach and landing were into the wind, on a heading variously reported as either west or parallel to runway 29; she landed uneventfully on a dry, level, dirt and grass field adjacent to the airport. After a brief discussion in which it was agreed that the chief pilot would demonstrate the next maneuver, the chief pilot attempted to lift off. According to the chief pilot, the right skid felt like it was "stuck" to the ground. Despite his efforts to correct the situation, he was unable to successfully set the helicopter fully back down. The helicopter rolled over onto its right side and sustained substantial damage. Immediately after they exited the helicopter, the two pilots attempted to determine what had caused the right skid to become stuck to the ground, but their efforts were curtailed by a fuel leak and small fire. The chief pilot did not report any prerollover mechanical deficiencies or failures of the helicopter, and a postaccident examination of the helicopter by Federal Aviation Administration (FAA) inspectors did not detect any such deficiencies or failures.

Single-rotor helicopters are susceptible to a lateral rolling tendency, called dynamic rollover, when lifting off, and the FAA Rotorcraft Flying Handbook noted that two "critical conditions" for dynamic rollover were "right side skid down" and "crosswinds from the left." Detailed evaluation of the wind data from two different nearby sensors revealed that the wind direction was between about 265 and 290 degrees, at 10 to 22 knots. Neither the wind direction at the accident site nor the exact heading of the helicopter were measured, so the crosswind component could not be accurately determined. However, given the lack of any other evidence supporting the event, it is likely that the helicopter experienced a dynamic rollover due to a left crosswind.

Text from the NTSB. Open the NTSB docket for WPR14LA159 for the full record.