Abstract: Two power line crews were placing insulators on six transmission towers for a 500-kilovolt overhead power line. The towers were 116 feet in height and were placed at 50-foot intervals, running east to west. Each tower was intended to hold a separate line running north to south. An aerial lift with a 90-foot articulated boom was used to place a power line worker on the fourth tower from the west. After placing the power line worker at a 100-foot height on the tower, the driver lowered and cradled the boom, retracted the outriggers, and drove the truck to the west. When the driver made a 180-degree turn around the western-most tower, the retracted boom struck and severed the tower's western guy. The loss of the guy caused the tower to collapse in an easterly direction and triggered a chain reaction. The lineman died when the tower on which he was working fell and crushed him.