Abstract: At approximately 11:30 a.m. on December 14, 2001, Employee #1 and coworkers were moving a Manitowoc 3900W crawler crane across a road. The power lines running along the road made it necessary to lower the gantry assembly onto the roof of the crane. The crane's boom had already been lowered onto a flatbed trailer truck and they intended to support the rear of the crane with a bucket loader. The truck developed a leak in its compressed air system that disabled its air brakes, so the mechanic/foreman went to a shop across the street and get what he needed to fix the truck. Since the job was delayed, the yard supervisor took one coworker to start him on different job. Shortly thereafter, Employee #1, the truck driver, and the crane operator decided to lower the gantry assembly. The crane operator entered the cab to work the controls, the driver stood on the right tread to act as a signalman, and Employee #1 went onto the roof of the crane to remove the pins holding the gantry's back hitches. The signalman was directed to boom down rapidly by Employee #1, but when excess slack developed in the cables, the gantry assembly achieved a snap-over-center configuration and slammed down onto the roof of the crane. The movement of the gantry assembly was so fast that Employee #1 was unable to get clear and he was crushed against one of the counterweights located on the crane's roof.