CHI00LA132
CHI00LA132

On May 6, 2000, at 1030 eastern daylight time, a Bell 206B helicopter was destroyed following a loss of tail rotor effectiveness landing near Eckerman, Michigan. The flight was conducted under the provisions of 14 CFR Part 135 and was on a visual flight rules flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot reported minor injuries to himself and one passenger. There were a total of four occupants including the pilot. The flight originated from the Cherry Capital Airport, Traverse City, Michigan at 0910.

After losing tail rotor effectiveness, the pilot was able to land the helicopter in a field amongst pine trees. The main rotor stuck the trees and the helicopter rolled over on its right side. A fire erupted and the helicopter was consumed. The occupants had exited the aircraft prior to the fire.

In a written statement, the pilot said that, as he approached the landing area, the helicopter was, "...about 250 pounds below max[imum] gross weight of 3,200 pounds." The pilot stated that, while on approach to land, he noticed a tree that he had not seen before and decided to abort the landing. He said he, "...began a power pull to 100 percent torque and a transition to forward flight. The helicopter immediately began a rapidly accelerating yaw to the right. I applied max[imum] left pedal to halt the yaw, which was ineffectual." The pilot stated that, when he was clear of obstacles, he attempted to regain control. He said that, at that point, he, "...believed [he] still had a functioning tail rotor, but that it may have entered a 'loss of tail rotor effectiveness' state and need only be regained." The pilot also stated that, "the 'low rotor RPM' warning light and horn began to come on with each pull of the collective..."

Federal Aviation Advisory Circular (AC) 90-95 "Unanticipated Right Yaw in Helicopters", which is appended to this report, states that a, "loss of translational lift results in increased power demand and additional anti-torque requirements." The AC also states that, "When operating at or near maximum power, this increased power demand could result in a decrease in rotor rpm ... Any reduction in the translational lift will result in an increase in power demand and anti-torque requirements." The AC further states:

"The following factors can significantly influence the severity of the onset of LTE. a. Gross Weight and Density Altitude. An increase in either of these factors will decrease the power margin between the maximum power available and the power required to hover. The pilot should conduct low-level, low-airspeed maneuvers with minimum weight. b. 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. c. Power Droop. A rapid power application may cause a transient power droop to occur. Any decrease in main rotor rpm will cause a corresponding decrease in tail rotor thrust. The pilot must anticipate this and apply additional left pedal to counter the main rotor torque. All power demands should be made as smoothly as possible to minimize the effect of the power droop."

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