Abstract: A heavy equipment mechanic with a major urban transit authority, was working on a truck equipped with a universal hy-rail. This truck was on a flat bed Ford 8000 Steco Boom Truck. The rear wheel assembly was raised with two 4-ton jacks and an L-shaped hook was installed to support the wheel assembly. The jacks were used only to raise the assembly to set the hook and were then removed. The employee was using a hammer to straighten a bracket under the left rear wheel of the hy-rail assembly. The L-shaped brackets failed to support the assembly and the assembly fell onto the employee, killing him by crushing his head between the left rear rail wheel and the bed of the boom truck.