Incident Sequence
On the day of the incident, the aircraft arrived at 0951. It was scheduled to depart at 1100 but was delayed due to a report from the previous flight crew of a takeoff slat warning light indication problem. After a maintenance check, pushback for the next flight occurred at 1206.
At 1224, while taxiing and completing pre-takeoff checks, the captain reported another takeoff slat warning light indication problem. Maintenance requested the captain return to the gate for further examination. At 1241, a maintenance technician assessed the problem and told the captain, "were gonna [sic] have to mess up with your takeoff condition here and you know after we do this, you're not supposed to move anything." The captain acknowledged.
Maintenance Check
The maintenance check procedures required advancing "either or both" engine throttles to verify the warning horn operation. The system was verified and the slats were set in the takeoff configuration. During the entire check, the captain and first officer remained seated.
Pushback and Movement
At 1251, the first officer called for and received pushback clearance. The engines were started during pushback. The captain stated that "prior to the engine start sequence, I did not direct re-accomplishment of the before start checklist." The captain said the pushback and initial engine start appeared normal. However, shortly after engine start and with the tug still attached, the airplane began to move forward under its own power. The captain noticed the throttles were still advanced. Both pilots reached to pull the throttles back to idle, but the airplane had moved enough to cause the tug and tow bar to jackknife to the left, striking the aircraft and leaving a 4-foot long gash in the fuselage. The captain shut down the engines, secured the cockpit, and assessed the situation.