Struck against a moving object
EE had set up crane to lift bed off 777A truck Crane was set up perpendicular to the truck & 3' lower in elevation. Rigging was hooked to bed 3 times. As truck bed was swung, the crane tilted toward truck bed slightly. EE started lowering load & began retracting the boom. Crane stopped tilting, EE thought everything was fine, but the crane suddenly laid against truck bed.