Flying over mountains in the southwestern United States, the Airbus Helicopters AS350 B3 dipped as low as 30 ft above ground level with fluctuating groundspeeds as high as 148 kt before abruptly entering a hard right bank and striking the ground.
The Dec. 15, 2015, crash in Superior, Arizona, killed the pilot and flight nurse and seriously injured the flight paramedic.
The U.S. National Transportation Safety Board (NTSB), in its final report on the accident, said the probable cause was the pilot’s “loss of helicopter control in mountainous terrain as the result of operating the helicopter outside the performance envelope of its hydraulic system and encountering the servo transparency phenomenon.”
The report cited as a contributing factor the pilot’s “decision to perform low-level, high-speed maneuvers through mountainous terrain.”
As explained in a 2003 NTSB study that quoted helicopter manufacturer Eurocopter (now Airbus Helicopters),1 servo trans…
