Accident Details
On May 2, 2012, at approximately 0920 central daylight time, a Bell 206B helicopter, registration N85RB, impacted terrain after a loss of control near Valley Falls, Kansas. The commercial pilot and two passengers sustained minor injuries. The helicopter, registered to a private individual and operated by Hawkeye Helicopters of Ottawa, Kansas, sustained substantial damage. Day visual meteorological conditions prevailed at the time, and no flight plan was filed for the 14 Code of Federal Regulations Part 91 aerial observation flight.
Witness Observations
Several witnesses reported seeing the helicopter spinning prior to the crash. The helicopter impacted the ground near a footpath bordered by trees. After impact, 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 short time following the accident.
Pilot Report
The pilot recounted that while hovering at an altitude between 100 and 150 feet above ground level, the helicopter began an uncommanded right turn. He applied full left pedal, left-forward cyclic, and a slight reduction of power in an attempt to stop the rotation. Sensing a loss of tail rotor effectiveness (LTE), the pilot continued these control inputs. Unable to halt the rotation, he elected to enter an autorotation, aiming for an open area between a row of trees.
Investigation Notes
The responding Federal Aviation Administration (FAA) inspector noted that the pilot reported a quartering tailwind during an out-of-ground-effect hover. The pilot initiated a right turn, after which the helicopter began to spin. The inspector added that the pilot had recently received his rotorcraft-helicopter rating based on prior military experience but had limited recent helicopter experience. According to the NTSB Pilot/Operator Aircraft Accident/Incident Report (Form 6120.1), the pilot reported 2,398 total flight hours in rotorcraft, with only 2.1 hours in the accident make and model.
Reference to FAA Advisory Circular
FAA Advisory Circular (AC) 90-95, "Unanticipated Right Yaw in Helicopters," dated February 26, 1995, describes loss of tail rotor effectiveness as a critical low-speed aerodynamic characteristic that can result in an uncommanded rapid yaw rate. The AC states that LTE may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots and is not related to a maintenance malfunction. Paragraph 6 notes that maneuvers in a high-power, low-airspeed environment with a left crosswind or tailwind can create conditions for unanticipated right yaw. Paragraph 9 advises avoiding tailwinds, out-of-ground-effect hover, and high-power demand situations, and recommends vigilance regarding wind and power conditions.