HARPSWELL, ME, USA
N2365S
Robinson R-22B
The pilot was traveling forward in a Robinson R22B at an airspeed of 10 to 20 knots, and an altitude of 230 feet above the ground, with a 15 to 21 knot left-quartering tailwind. The helicopter began to rotate to the right. After three rotations the pilot was unable to recover, and the helicopter impacted terrain. FAA Advisory Circular (AC) 90-95 stated that loss of tailrotor effectiveness (LTE) was a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded rapid yaw rate, and loss of aircraft control. It also stated that all single main rotor helicopters were susceptible to loss of tail rotor effectiveness (LTE). The AC advised pilots that when maneuvering between hover and 30 knots to avoid: left crosswinds, tailwinds, and high power settings at low airspeeds.
On July 11, 2000, about 1005 Eastern Daylight Time, a Robinson R-22B, N2365S, was substantially damaged while maneuvering near Harpswell, Maine. The certificated private pilot sustained serious injury, and the passenger was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local photography flight conducted under 14 CFR Part 91. The flight originated from a private airstrip at South Harpswell, Maine, about 0930. The pilot stated he was flying northeast about 10 to 20 miles per hour. He was approximately 230 feet above the ground. The helicopter began to rotate to the right, and seemed as if it was inverted. The pilot applied full left pedal, and lowered the collective. After about three rotations, the pilot heard a horn, which he believed was a low rotor RPM warning. Initial pilot inputs did not correct the loss of control. As the helicopter descended toward trees, the pilot applied full left cyclic, followed by full forward cyclic, followed by full right cyclic. The helicopter seemed slightly more controllable, and was no longer inverted. However, it was still "corkscrewing" to the right. It impacted a swampy area, and the fuselage, tailboom, and tailrotor were damaged. Examination of the wreckage by a Federal Aviation Administration inspector did not reveal any pre-impact mechanical malfunctions. The reported winds at an airport approximately 7 miles from the accident site, at 0955, were from 300 degrees at 15 knots, gusting to 21 knots. The FAA issued advisory circular AC-90-95, Unanticipated Right Yaw in Helicopters, during February 1995. The AC stated that the loss of tail rotor effectiveness (LTE) was a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded rapid 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, "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 stated: "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 8 of the AC stated: "OTHER FACTORS...Low Indicated Airspeed. At airspeeds below translational lift, the tail rotor is required to produce nearly 100 percent of the directional control. If the required amount of tail rotor thrust is not available for any reason, the aircraft will yaw to the right." Paragraph 9 of the AC stated: "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... (6) Stay vigilant to power and wind conditions." After a written and verbal request, the pilot failed to return the National Transportation Safety Board Pilot/Operator Aircraft Accident Report. Additionally, he told a FAA inspector that the maintenance logbooks were missing.
The pilot-in-command's improper in-flight decision to maneuver at a low airspeed with a left-quartering tailwind which resulted in a loss of tailrotor effectiveness.
Source: NTSB Aviation Accident Database
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