scope:

Description of Driving Event:

After completion of the rotation of the Z-1 truss segment using a cab-operated 30-ton overhead bridge crane, the lifting device down rods were disconnected from the flight hardware. The task leader instructed the crane director on the floor to move the crane hook up to clear the trunnions. The crane director relayed the instructions over walkie-talkie radio to the crane operator in the cab. The crane operator inadvertently commanded the hook to move in the down direction causing the lifting device down rods to make contact with the trunnions on the Z-1 truss. The operation was stopped. After examination by the task team, the crane hook was moved up and the crane was placed in the parking area and impounded. There was evidence that all four trunnions received metal-to-metal contact from the down rods. A damage assessment is being conducted. There was no damage to the lifting device or Hydra-Set and no personnel were injured.

Root cause: The root cause was determined to be human error caused by a combination of less than optimum design of the crane cab controls; inadequate communications and understanding of hoist speeds; and the failure of the emergency stop-button operator to actuate the emergency stop.