CEN12LA267
CEN12LA267

On May 2, 2012, about 0920 central daylight time, a Bell 206B Helicopter, N85RB, impacted terrain following a loss of control, near Valley Falls, Kansas. The commercial rated pilot and two passengers received minor injuries. The helicopter sustained substantial damage. The helicopter was registered to a private individual and operated by Hawkeye Helicopters, Ottawa, KS. Day visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91 aerial observation flight.

Several witnesses reported the helicopter “spinning” before the crash. The helicopter impacted the ground near a footpath, with trees on either side of the path. The helicopter came to rest on its left side, with the tailboom and left skid separated from the fuselage. The pilot stated that the engine continued to run for a brief time after the accident.
The pilot reported that during a 100-150 agl (above ground level) hover, the helicopter started an uncommanded right turn. He applied left full pedal, left-forward cyclic, and a slight reduction of power, to stop the rotation. The pilot added that he sensed the loss of tailrotor effectiveness (LTE), and continued with the control inputs to fly out of the LTE. Unable to get the helicopter to stop rotating, the pilot elected to enter an autorotation aiming for an open area, between a row of trees.

The responding Federal Aviation Administration (FAA) inspector stated that the pilot reported that during an out-of-ground hover, the helicopter had a quartering tailwind. The pilot initiated a right turn and the helicopter started to spin. The inspector added that the accident pilot had recently received his rotorcraft-helicopter rating based on prior military experience; however, the pilot did not have much recent helicopter experience. On the NTSB Pilot/Operator Aircraft Accident/Incident Report, 6120.1 form, the pilot reported a total of 2,398 flight hours in rotorcraft, with 2.1 hours in the accident make/model of helicopter.

FAA Advisory Circular (AC) 90-95, Unanticipated Right Yaw in Helicopters, dated February 26, 1995 states that the loss of tail rotor effectiveness (LTE) is a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, could result in the loss of aircraft control. It also states, "LTE is not related to a maintenance malfunction and may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots."

Paragraph 6 of the AC covered conditions under which LTE may occur. It states:
"Any maneuver which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where unanticipated right yaw may occur."

Paragraph 9 of the AC states: "When maneuvering between hover and 30 knots: (1) Avoid tailwinds. If loss of translational lift occurs, it will result in an increased high power demand and an additional anti-torque requirement. (2) Avoid out of ground effect (OGE) hover and high power demand situations, such as low-speed downwind turns. (3) Be especially aware of wind direction and velocity when hovering in winds of about 8-12 knots (especially OGE). There are no strong indicators to the pilot of a reduction of translation lift. (4) Be aware that if considerable amount of left pedal is being maintained a sufficient amount of left pedal may not be available to counteract an unanticipated right yaw. (5) Be alert to changing aircraft flight and wind conditions which may be experienced when flying along ridge lines and around buildings. (6) Stay vigilant to power and wind conditions."

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