On November 7, 2006, at 2200 central standard time, a Boeing 717-200, N904ME, operated as Midwest Airlines flight 157 contacted a Boeing 717-200, N923ME, which was being operated as Midwest Airlines flight 406, during ground operations at the Mitchell International Airport (MKE), Milwaukee, Wisconsin. There were no injuries to the 2 flight crew members, 2 flight attendants, and 26 passengers on board flight 157, or to the 2 flight crew members, 2 flight attendants, and 25 passengers on board flight 406. There was minor damage to the right horizontal stabilizer on N904ME, and substantial damage to the left horizontal stabilizer on N923ME. Both airplanes were operating under 14 CFR Part 121, scheduled passenger service at the time of the accident. Instrument meteorological conditions prevailed and instrument flight rules flight plans were filed for both airplanes. N904ME was en route to Eppley Field (OMA), Omaha, Nebraska, and N923ME was en route to the Kansas City International Airport (MCI), Kansas City, Missouri. Flight 157 was parked at gate D36 prior to the accident and flight 406 was parked next to it at gate D34. Flight 157 was pushed back from the gate and was stopped facing east behind flight 406 and perpendicular to the gates. The captain reported the pushback was normal and the airplane was not positioned any closer to the gates than usual. The captain of flight 406 stated they were ready to push back, but were advised by the tug driver that they could only push back a little because there was an airplane behind them (flight 157). The captain advised the tug driver to push the airplane back as much as possible so they would be credited with an on-time departure. The tug driver for flight 406 stated he could not see flight 157 behind them and as soon as he began moving the airplane both wing walkers gave the "X" signal to stop. He stated the airplane had been pushed back approximately 5-6 feet. One wing walker stated their wands were up in an "X" prior to flight 406 being moved because of the location of flight 157 behind them. The captain stated that after the airplane was pushed back, he set the brakes and they were stationary for 3-5 minutes prior to the impact. The captain of flight 157 stated his airplane was then marshalled forward. As he made a left turn out, they felt a jolt so he stopped the airplane and contacted the ramp personnel to see what happened. He reported the left turn was not sharp. The marshaller for flight 157 stated the airplane moved forward very little if at all prior to starting the left turn. The damage to N904ME, flight 157, consisted of minor damage to the outboard corner of the right side elevator trim tab end cap. Damage to N923ME, flight 406, consisted of substantial damage to the left side elevator and the left side elevator trim tab. Following this accident a red Pushback Clearance Reference Line was painted on the ramp area perpendicular to gates D30-D38. Midwest Airlines then issued a Ramp Training Procedural Communication stating that when an airplane is pushed back from the gate, both main landing gear must be on the alley side of the Pushback Clearance Reference Line at all times. In addition, Midwest Airlines reported they are revising their Company Operations manual to prohibit "Partial Push Backs" for the purpose of recording an on-time departure. The revision will also state that push backs will not be initiated until the area behind and on both sides of the airplane is clear of obstructions so that a complete, uninterrupted push back can be accomplished.