DFW05LA239

On September 7, 2005, approximately 1830 central daylight time, a single-engine Bell 206B helicopter, N230CA, was substantially damaged following a loss of control while maneuvering near New Orleans, Louisiana. The commercial pilot and a passenger sustained minor injuries. The other passenger was not injured. The helicopter was registered to Go Interest, LLC., and operated by Helitrans Corporation Incorporated, of Manvel, Texas. A visual flight rules flight plan was filed for the photo flight that originated from the Ryan Field (BTR), near Baton Rouge, Louisiana, approximately 1645. Visual meteorological conditions prevailed for the flight conducted under 14 Code of Federal Regulations Part 91.

Prior to departure, the 524-hour pilot received a unique transponder code that would allow the helicopter to conduct flight operations in the temporary flight restriction area that was established around New Orleans following Hurricane Katrina. The flight was uneventful until the pilot began a series of left hand orbits over a neighborhood. The pilot said that during the third orbit, he was at an altitude of approximately 500 feet above ground level (agl) at 40 knots, when the helicopter suddenly pitched-up and entered an uncommanded right turn. The pilot responded by applying left anti-torque pedal input but, there was no response. He then lowered the nose and followed the right turn. In an attempt to stop the rotation, the pilot lowered the collective and this action "appeared to help." He then observed power lines ahead and "pulled back on the cyclic and up on the collective" to clear the power lines. Subsequently, the helicopter turned approximately 180-degrees and impacted the roof of a house, where it came to rest. The pilot and passengers reported immediately seeing a military UH-60 Black Hawk helicopter hovering above them as they exited the helicopter, which assisted in their recovery. The operator was concerned that the Black Hawk's proximity to the helicopter may have contributed to a loss of tail rotor effectiveness. However, the pilot said that he had observed many military helicopters operating in the area and was unable to confirm that the Black Hawk had contributed to the accident. The pilot was also unsure as to what may have caused the loss of tail rotor effectiveness.

On October 31, 1983, Bell Helicopter published an Operations Safety Notice regarding loss of tail rotor effectiveness in the Model 206B and similar airframes. Bell Helicopter describes the phenomenon of loss of tail rotor effectiveness as "Unanticipated Right Yaw." According to the Safety Notice: "When maneuvering between hover and 30 mph: Be aware that a tail wind will reduce relative wind speed if a down wind translation occurs. If loss of translational lift occurs it can result in a high power demand and an additional anti-torque requirement. Be alert during hover (especially OGE) and high power demand situations. Be alert during hover in winds of about 8-12 knots (especially OGE) since there are no strong indications to the pilot, to the possibility of a reduction of translational lift. This reduction results in an unexpected high power demand and increased anti-torque requirements. Be aware that if a considerable amount of left pedal is being maintained, that a sufficient amount of left pedal may not be available to counteract an unanticipated right yaw. Be alert to changing aircraft flight and wind conditions such as experienced when flying along ridgelines and around buildings. Observe the relative wind conditions set out in the attached chart."

The chart depicts a helicopter facing 360 degrees over a compass rose. One shaded area of the chart depicts winds from between 120 degrees and 240 degrees, at wind speeds above 5 knots and up to 17 knots. According to a note on the chart: "An unanticipated right yaw may occur when operating in the shaded areas of the chart." According to FAA Advisory Circular (AC) 90-95, "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 AC also advised of greater susceptibility for loss of tail rotor effectiveness (LTE) in right turns and the phenomena may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots.

According to the manufacturer, if a sudden unanticipated right yaw occurs, the following recovery technique should be performed:

1. Pedal - Full left; simultaneously, cyclic - forward to increase speed.

2. As recovery is effected, adjust controls for normal forward flight.

The following CAUTION is also provided: "Collective pitch reduction will aid in arresting the yaw rate, but may cause an excessive rate of descent. The subsequent large rapid increase in collective to prevent ground contact, may further increase the yaw rate and decrease rotor rpm. The decision to reduce collective must be based on the pilot's assessment of the altitude available for recovery."

3. If the spin cannot be stopped and ground contact is imminent, an autorotation may be the best course of action. Maintain full left pedal until the spin stops, then adjust to maintain heading.

At 1753, the automated surface observing system (ASOS) at the Louis Armstrong International Airport (MSY), near New Orleans, Louisiana, reported wind from 300 degrees at 5 knots, visibility 10 statute miles, haze, few clouds at 3,000 feet, scattered clouds at 7,500 feet, broken clouds at 20,000 feet and 25,000 feet, temperature 84 degrees Fahrenheit, dew point 72 degrees Fahrenheit, and a barometric pressure of 29.95 inches of Mercury.