What happened
On July 3, 2014, at 1715 PDT, an American Eurocopter Corp. AS350B3, registration N832PA, was performing an external load supply drop on a mountain ridge approximately 54 miles east of Fallon, Nevada. The helicopter was operating under an exclusive contract to the Bureau of Land Management, transporting a 972-pound load via a 100-foot long line.
As the pilot approached the drop zone at an elevation of 8,600 feet mean sea level, the load was approximately 10 feet above the ground when the aircraft began swaying laterally and suddenly descended. The pilot attempted to correct the descent by increasing collective and applied right pedal to counter a leftward yaw. Although the pilot set the load down, the helicopter continued to rotate left and descend. The aircraft landed hard and rolled onto its right side. The impact caused the rotor blades to fragment and a small fire to emerge from the engine compartment, which extinguished itself. The pilot sustained one minor injury, and there were no fatalities.
The investigation
Investigators examined the wreckage on a barren hilltop, noting that the right main landing skid had separated from the airframe and the tail boom had separated forward of the tail rotor gearbox. The engine, a Turbomechan Arriel 2D, showed thermal damage from a post-crash fire. Analysis of the Engine Data Recorder (EDR) showed that 16 seconds before the end of the recording, there was a steady rise in collective, an increase in N1 (gas generator turbine) to 102.5 percent, and a subsequent drop in N2 (main rotor rpm) to 378 rpm. A fault was detected one second before the end of the data, consistent with the main rotor striking the ground.
Technical evaluations of the external load confirmed the total weight of the load, line, and hook was 942 pounds. Maintenance records indicated the aircraft had completed a 300-hour inspection in April 2014 and a daily inspection on June 30, 2014.
Findings
Analysis of the meteorological conditions revealed that while surface winds were between 5 and 15 knots, the atmosphere was unstable. Winds flowing down the leeward side of the ridge were likely gusting between 5 and 25 knots, creating turbulence and downward pressure. The investigation concluded that the combination of irregular wind conditions, high operating altitude, and the high-power, low-airspeed state of the aircraft created an environment conducive to the development of a loss of tail rotor effectiveness (LTE), leading to the loss of directional control.