What happened
On November 7, 2017, a Hughes 369D helicopter, registration N138WH, was performing an external load flight near Sulphur, Louisiana. The mission, operated by Winco, Inc., involved installing guard ropes between deenergized 500-kilovolt power transmission lines.
During the operation, the pilot maintained a hover to allow two linemen to work on the transmission line bundles. After the linemen had secured a guard rope to the center conductor bundle, the pilot repositioned the aircraft to allow work on the northern conductor bundle. While the pilot was maneuvering the helicopter into the wind to move the linemen away from the conductor, the 60-foot synthetic long line made contact with a braided steel shield wire suspended between power towers.
The contact caused the long line to sever approximately midspan. The two linemen were fatally injured when they fell approximately 100 feet to the ground. The pilot subsequently returned to a temporary landing zone and landed without further incident. Weather at the time was visual meteorological conditions with a 10-mile visibility.
The investigation
Investigators examined the 60-foot synthetic long line, which was made of Amsteel Blue synthetic fiber. It was noted that the line was not equipped with an abrasion-resistant cover. While a 100-foot line with an abrasion-resistant cover was available at the landing zone, the line used in the accident lacked this protection.
Video footage of the flight confirmed that the long line severed following lateral contact with the braided steel shield wire. The pilot reported no mechanical malfunctions or failures of the N138WH that would have prevented normal operation.