American Eurocopter Corp AS350B3 N3948A accident near Encino, Texas

Probable cause

The pilot’s failure to maintain directional control while maneuvering, which resulted in a loss of tail rotor effectiveness. Contributing to the accident were the pilot’s limited experience in the operating environment and lack of formal mission training.

NTSB analysis

The pilot reported that he descended the helicopter from 800 to 150 feet above ground level and then hovered on a southerly heading. The helicopter began to drift to the southeast, so the pilot repositioned the helicopter by making a left climbing turn. The wind was from the southeast with gusts estimated by the flight crewmembers to be 15 to 20 knots. As the helicopter turned left, it experienced a change from a right quartering tailwind to a left quartering tailwind, a flight environment associated with the onset of loss of tail rotor effectiveness. According to the pilot, the helicopter shuddered and spun rapidly left. The pilot applied full right pedal and attempted to accelerate because he believed that he had regained control. However, the helicopter then continued to spin left and subsequently impacted trees and terrain. The helicopter sustained substantial damage to the fuselage, main rotor blades, and tail rotor. The pilot stated that he heard a sound similar to the low rotor rpm horn before impact.

The pilot reported no preimpact anomalies with the helicopter. A postaccident examination of the helicopter and engine revealed no mechanical malfunctions or failures that would have precluded normal operation. The vehicle engine monitoring display (VEMD) recorded an overtorque event and a free turbine overspeed event consistent with the main rotor blades striking the trees and ground and the main gear box coupling separating on impact. The VEMD also recorded a gas generator overspeed event consistent with the engine producing power at the time of impact. The VEMD did not record any preimpact events that would have precluded normal engine operation. On the basis of the evidence, it is likely that the pilot failed to maintain directional control while maneuvering, which resulted in a loss of tail rotor effectiveness.

Text from the NTSB. Open the NTSB docket for CEN14GA109 for the full record.