FTW00LA100

The pilot was maneuvering the helicopter to land on an offshore platform. He initially approached the platform from the north, heading into the wind, which was from the south-southeast at 20-25 knots. The pilot began a right turn to circle clockwise around the platform at 300 to 400 feet agl and 70 to 80 mph indicated airspeed. Approximately 3/4 of the way around the platform, the helicopter 'began to spin' to the right. The pilot applied left pedal in an attempt to stop the spin, however, there was 'no tail rotor response.' The pilot 'made an effort to try to come out of [the spin] by lowering the collective and dropping the nose of the aircraft.' Control inputs had no effect on stopping the spin, and the helicopter descended and impacted the water. There were no reported anomalies to the tail rotor system prior to the accident. In February 1995, the FAA issued an Advisory Circular (AC 90-95) concerning unanticipated right yaw in helicopters, or loss of tail rotor effectiveness (LTE). The AC advises pilots LTE may occur in right turns at low airspeeds, and that correct, timely response is critical to prevent a loss of control.

On March 20, 2000, at 1524 central standard time, a Bell 206B3 helicopter, N5002E, was substantially damaged when it impacted the water while maneuvering near the Brazos 542 offshore platform in the Gulf of Mexico. The helicopter was owned by G.M. Leasing Co. L.L.C., of Broussard, Louisiana, and operated by Horizon Helicopters, Inc., of Angleton, Texas. The commercial pilot and his two passengers received minor injuries. Visual meteorological conditions prevailed, and a company flight plan was filed for the 14 Code of Federal Regulations Part 135 on-demand air taxi flight. The flight originated from the Brazos 341 offshore platform at 1500.

According to the pilot's statement, the pilot was transporting two passengers to the Brazos 542 offshore platform for either a landing or visual observation. The helicopter approached the platform from the north and was traveling "pretty much into the wind" in a southerly direction. The pilot reported the wind was about 20-25 knots from the south-southeast. The pilot stated that due to the offshore platform configuration, the landing had to be a "downwind or crosswind landing." The pilot began a right turn to circle clockwise around the platform at 300 to 400 feet agl and 70 to 80 mph indicated airspeed. Approximately 3/4 of the way around the platform, the helicopter "began to spin" to the right. The pilot applied left pedal in an attempt to stop the spin, however, there was "no tail rotor response." The pilot reported that "the antitorque pedal seemed to have no effect on controlling the aircraft. The spinning became greatly intensified, increasing in speed with each spin." The pilot "made an effort to try to come out of [the spin] by lowering the collective and dropping the nose of the aircraft, but this had no effect on stopping the spin and [the helicopter] was dropping rapidly." The pilot continued to try to "fly" out of the spin, and "about 2 seconds" before impact, the pilot pulled up the collective to "lessen the impact on the water." The helicopter impacted the water and rolled inverted.

According to the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the main rotor, transmission, tail rotor, tail rotor gearbox, and vertical fin separated from the helicopter when it contacted the water. The operator reported no anomalies to the tail rotor system prior to the accident.

The FAA issued Advisory Circular (AC-90-95), Unanticipated Right Yaw in Helicopters, in February 1995. The AC stated that the loss of tail rotor effectiveness (LTE) was a critical, low-speed areodynamic flight characteristic which could result in an uncommanded right yaw rate which did not subside of its own accord and, if not corrected, could result in the loss of aircraft control. It also stated, "There is a greater susceptibility for LTE in right turns. This is especially true during flight at low airspeed since the pilot may not be able to stop rotation. The helicopter will attempt to yaw to the right. Correct and timely pilot response to an uncommanded right yaw is critical. The yaw is usually correctable if additional left pedal is applied immediately. If the response is incorrect or slow, the yaw rate may rapidly increase to a point where recovery is not possible."