NTSB Factual Report

On September 2, 2001, approximately 1150 mountain daylight time, a McDonnell Douglas 369E helicopter, N440TJ, operated by Omni Aviation of Carencro, Louisiana, was substantially damaged when it collided with terrain while hovering near Kemmerer, Wyoming. The commercial pilot, the sole occupant aboard, was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for this work use flight being conducted under Title 14 CFR Part 133. The helicopter departed a nearby landing zone approximately 1145.

According to the pilot, he was transporting bags of seismic equipment by long line to a remote site. He said while he hovered into the wind and waited for a flagger, "a [wind] gust caused the helicopter to start to turn right." He applied "more left pedal," but was unable to stop the rotation. He jettisoned the external load, lowered the collective control, and attempted to fly out of the condition. He was able to stop most of the rotation but not before the helicopter struck the terrain. Both skid legs, tail rotor blades, and tail rotor gearbox broke off. The left horizontal stabilizer was struck by one of the blades, and the tail boom buckled when it struck the ground. The pilot said the winds were "generally light and variable, with [an] occasional gust."

According to FAA's Advisory Circular (AC) 90-95, loss of tail rotor effectiveness (LTE) "is a critical, low-speed aerodynamic flight characteristic that can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control. Some of the conditions conducive to LTE include (1) a high power setting, (2) low airspeed, and (3) a tailwind or left crosswind

NTSB Probable Cause

loss of tail rotor effectiveness while hovering. A contributing factor was the wind gust.