Helicopter Downed by Downdraft During Power Line Patrol in Mountainous Terrain (N997GM)

Incident Overview

A helicopter conducting a power line patrol flight in mountainous terrain was forced into the ground by a strong downdraft, according to the investigation. The pilot was flying 100 feet to the right of the power line in a 10 to 18 knot headwind. The aircraft's airspeed was between 70 and 80 knots at an altitude of 400 feet above ground level, with power set between 70 and 80 percent torque.

Sequence of Events

While executing a turn to continue following the power line, a strong downdraft pushed the helicopter downward despite the pilot's efforts to regain control. The helicopter struck snow-covered terrain and subsequently rolled over.

Flight Conditions

The flight took place in mountainous terrain, with the helicopter operating close to the power line. The headwind conditions were reported as 10 to 18 knots. No other environmental factors or aircraft parameters were specified in the source.