CEN12LA258

The pilot reported that he was aware of lightning and a thunderstorm that was close to the airport and approaching from the southwest. He was flying an approach to the southeast and planned to approach “straight in” to the hangar. As he began to flare to stop the descent, movement of the cyclic stick was briefly hindered by a laptop computer in the left seat passenger’s lap; the passenger immediately moved the obstructing laptop computer. The helicopter was then about level with the hangar roof when, according to the pilot, a strong gust of wind forced the helicopter’s nose up, and the helicopter briefly entered into a climbing right turn. The helicopter then began a sudden uncommanded turn, spinning to the right. The pilot reported that left pedal input had no effect and that he had only partial control as the helicopter made a full 360-degree turn, descended, and impacted the ground. During the impact with the ground, the lower fuselage sustained crushing damage, and the main rotor separated from the main rotor mast. A significant amount of fuel spilled during the impact, but no postimpact fire occurred. After the crash, both occupants were able to extract themselves from the wreckage unassisted. According to a weather observation station at the airport, the wind was from 120 degrees at 19 knots, gusting to 25 knots, and a thunderstorm was recorded on the field. Federal Aviation Administration Advisory Circular 90-95, “Unanticipated Right Yaw in Helicopters,” describes loss of tail rotor effectiveness (LTE) as a critical, low speed aerodynamic flight characteristic that could result in an uncommanded rapid yaw rate that does not subside of its own accord and, if not corrected, could result in the loss of aircraft control. The pilot was operating the helicopter in a low airspeed, out-of-ground-effect, high-power-demand flight condition, which could have resulted in LTE.

On April 26, 2012, about 1645 central daylight time, a Bell 206B helicopter, N2068X, impacted terrain while landing at Rick Husband Amarillo International Airport (AMA), Amarillo, Texas. The pilot and passenger suffered minor injuries and the helicopter was substantially damaged. The helicopter was registered to and operated by Chesapeake Bay Helicopters Inc., under the provisions of 14 Code of Federal Regulations Part 91, as an aerial surveillance flight. Day visual meteorological conditions prevailed and a visual flight rules flight plan was not filed. The helicopter was destined for AMA and had departed about 1600 from Moore County Airport (DUX), Dumas, Texas. The pilot was aware of lightning and a thunderstorm that was close and approaching the airport from the southwest. He was flying an approach to the southeast and was landing “straight in to the hangar”. As he began to flare to stop the descent his cyclic stick was briefly hindered by interference from a laptop computer in the left seat passenger’s lap and the passenger immediately moved the obstructing laptop computer. The helicopter was then about level with the hangar roof and the pilot reported that a strong gust of wind forced the helicopter’s nose up and it briefly entered into a climbing right turn. The helicopter then began a sudden uncommanded turn spinning to the right. The pilot reported that left pedal input had no effect and he had only partial control as the helicopter made a full 360 degree turn, descended, and impacted the ground. During the impact with the ground the lower fuselage sustained crushing damage and the main rotor separated from the main rotor mast. There was a significant fuel spill during the impact, but no postimpact fire. After the crash both occupants were able to extract themselves from the wreckage unassisted. An examination of the helicopter revealed no preimpact mechanical anomalies or malfunctions that would have precluded normal operations. At 1653 an automated weather observation facility at AMA reported: wind from 120 degrees at 19 knots gusting to 25 knots, visibility 10 miles or greater, thunderstorm, few clouds at 9,000 feet above ground level (agl), scattered clouds at 11,000 feet agl, temperature 28 degrees Celsius, dew point temp 14 degrees Celsius, altimeter 29.84 inches of Mercury, peak wind during previous hour from 110 degrees at 27 knots at 1634, thunderstorm began at 1647. Federal Aviation Administration Advisory Circular (AC) 90-95, “Unanticipated Right Yaw in Helicopters,” issued in February 1995, described loss of tail rotor effectiveness (LTE) as a critical, low speed aerodynamic flight characteristic that could result in an uncommanded rapid yaw rate that does not subside of its own accord and, if not corrected, could result in the loss of aircraft control. The AC 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…Anymaneuver 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.” When operating at airspeeds below effective translational lift, pilots should avoid OGE hover and high power demand situations...