Bell 206B N150SP accident near Shepherd, Montana

Probable cause

The pilot’s loss of control while maneuvering during low-altitude operations due to sudden neurological impairment or incapacitation and the helicopter’s subsequent collision with power lines.

NTSB analysis

The pilot was maneuvering at low altitude during cattle herding operations. The helicopter collided with power lines and subsequently impacted terrain. Power lines were found wrapped around the main rotor mast about 25 times. Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

A small amount of acute blood was found in the left ventricle of the pilot's brain, but no significant traumatic injuries were found; thus, it is likely the hemorrhage occurred during an acute premortem event. Given the autopsy findings and that the pilot knew the flying area well and would have likely known where the power lines were located, it is likely that he was impaired or incapacitated by an acute neurologic event in the seconds before impact with the power lines.

Text from the NTSB. Open the NTSB docket for WPR13FA208 for the full record.