20000312017979A

(.4)The airplane was taxiing to the runway for departure when the APU door light illuminated. The airplane returned to the loading dock, the engines were shut down, and the APU door was closed and secured. The airplane's engines were then restarted, and the airplane began another pushback. One maintenance technician was wearing a headset, and was located off the right side of the airplane. Another technician was driving the tug. After receiving clearance to push, the tug driver made a gradual turn to avoid equipment and minimize jet blast to other gates. Halfway down the ramp, the airplane contacted the loading dock, and suffered an 8-foot gash along the left side, below the cockpit area. The tug operator stated that the tug's drive mechanism was sticking in a '2-wheel,' or 'crab' mode. Post-accident investigation of the tug revealed no discrepancies, although other technicians subsequently complained of the same intermittent problem. Components were removed for testing, with no anomalies found. However, once those components were replaced, there were no additional problems with the tug. A representative from the tug's manufacturer stated that regardless of system status, the operator would always have had front wheel steering and braking. (-23) on push-back from the loading dock gate #3, driver turned too soon, causing damage to left hand side of forward side under pilot's window. Damage about by 8' x 1' denting and ripping through pressurized section. Some frames were out and dented.