Accident Details
On April 26, 2012, at approximately 1645 central daylight time, a Bell 206B helicopter, registration N2068X, was damaged when it struck the ground while landing at Rick Husband Amarillo International Airport (AMA) in Amarillo, Texas. The helicopter, operated by Chesapeake Bay Helicopters Inc. under 14 Code of Federal Regulations Part 91, was on an aerial surveillance flight. The pilot and passenger sustained minor injuries. The flight originated from Moore County Airport (DUX) in Dumas, Texas, at about 1600.
Day visual meteorological conditions prevailed; no visual flight rules flight plan was filed. The pilot reported awareness of lightning and a thunderstorm approaching the airport from the southwest. He was flying a southeast approach and planned to land straight into a hangar. During the flare to arrest descent, the cyclic stick was briefly obstructed by a laptop computer resting in the left seat passenger's lap. The passenger promptly moved the laptop. At that moment, the helicopter was approximately level with the hangar roof. The pilot described a strong gust of wind that forced the helicopter's nose upward, initiating a climbing right turn. Subsequently, the helicopter experienced a sudden uncommanded right spin. The pilot noted that left pedal input had no effect and he had only partial control as the helicopter completed a 360-degree rotation, descended, and impacted the ground.
Weather Information
At 1653, the automated weather observation facility at AMA reported wind from 120 degrees at 19 knots gusting to 25 knots, visibility 10 statute miles or greater, thunderstorm, few clouds at 9,000 feet above ground level (agl), scattered clouds at 11,000 feet agl, temperature 28°C, dew point 14°C, and an altimeter setting of 29.84 inches of Mercury. The peak wind during the previous hour was from 110 degrees at 27 knots recorded at 1634. The thunderstorm began at 1647.
Post-Accident Examination
Impact damage included crushing of the lower fuselage and separation of the main rotor from the main rotor mast. A significant fuel spill occurred, but there was no postimpact fire. Both occupants extricated themselves unassisted. Examination of the helicopter revealed no preimpact mechanical anomalies or malfunctions that would have precluded normal operations.
Background on Loss of Tail Rotor Effectiveness
Federal Aviation Administration Advisory Circular (AC) 90-95, titled "Unanticipated Right Yaw in Helicopters" (issued February 1995), describes loss of tail rotor effectiveness (LTE) as a critical low-speed aerodynamic flight characteristic that can result in an uncommanded rapid yaw rate not subsiding on its own, possibly leading to loss of control. The AC notes that LTE is not related to a maintenance malfunction and can occur in varying degrees in all single main rotor helicopters at airspeeds below 30 knots. Maneuvers requiring high power and low airspeed with a left crosswind or tailwind create conditions conducive to unanticipated right yaw. Pilots are advised to avoid out-of-ground-effect hover and high-power-demand situations when operating below effective translational lift airspeeds.