ATL04TA137
ATL04TA137

On June 22, 2004, at 1000 central daylight time, a Bell 206B, N3902W, registered to Alabama State Department of Public Safety, operating as a 14 CFR Part 91, Public Use flight, collided with trees and a road in the vicinity of Graysville, Alabama. Visual meteorological conditions prevailed. A company flight plan was filed and a commerical weather briefing was obtained. The helicopter was destroyed. The commercial pilot and pilot rated passenger reported no injuries. The flight originated from Bessemer, Alabama, on June 22, 2004, at 0900.

The pilot stated he flew to an area located 10 to 12 miles northwest of Birmingham, Alabama, in the vicinity of Graysville, Alabama. He was at a low airspeed between 20 to 25 knots at 200 feet AGL. making a turn to his right with a tail wind. The helicopter started to weathervane and started an uncommanded turn to the right. He immediately applied left anti torque pedal and increased power. The un-commanded turn rate increased. He decreased power, lowered the nose, and applied right cyclic. The turn rate increased. The helicopter collided with trees, and a road while turning to the right collapsing the right skid and rolled over on its left side. When asked if he experienced any mechanical problems with the helicopter before the accident, the pilot stated no. When asked what happened, the pilot stated "he encountered a loss of tail rotor effectiveness". When asked if he had any training in regards to loss of tail rotor effectiveness, he stated only open discussion.

Advisory Circular 90-95 states, "Loss of tailrotor Effectiveness is a critical, low speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside on its own accord and if not corrected, can result in a loss of aircraft control. 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. LTE is not necessarily the result of a control margin deficiency....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....The aircraft characteristics and relative wind azimuth regions are:...Weathercock stability (120-degrees to 240-degrees.) (See figure 2.) Tailwinds from 120-degrees to 240-degrees, like left crosswinds, will cause a high pilot workload. The most significant characteristics of tailwinds is that they are a yaw rate accelerator. Winds within this region will attempt to weathervane the nose of the aircraft into the relative wind."






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