Aircraft and Conditions
A McDonnell Douglas DC-9-32 was parked at the gate. The auxiliary power unit (APU) was inoperative. The ramp was covered with snow and ice.
Pushback Procedure
The captain reported that a single-engine cross-bleed start would require about 80% N1 on the operative engine, so he decided to start both engines at the gate and then proceed with pushback. According to the operator's manual, if a headset was used, it was to be worn by the tug driver. However, the tug driver did not wear the headset because its cord had been broken and repaired multiple times and was too short to reach the tug driver. Instead, a walker near the nose of the airplane wore the headset.
The Incident
During pushback, the tug driver attempted to push the nose of the airplane to the west. The airplane encountered icy conditions, moved forward, and struck the tug. At the time of loss of traction, the tug was nearly 90 degrees to the right side of the airplane's nose. The tug driver observed the forward movement and stopped the tug, but without a headset, he could not notify the cockpit crew. The walker wearing the headset reported that he was looking away and did not see the airplane moving forward in time to call the cockpit.
The pushback was performed by a contract crew that had been trained in accordance with the airline's Ground Movement Manual (GMM). The GMM did not contain specific directions for pushbacks on icy surfaces.