On May 17, 2005, at 0856 mountain daylight time, a Boeing 737-322, N305UA, operated by United Air Lines, flight 229, sustained minor damage when it collided with N373UA, another Boeing 737-322 operated by United Air Lines, flight 424, while taxiing at Denver International Airport (DEN), Denver, Colorado. Visual meteorological conditions prevailed at the time of the incident. Both flights were being conducted with instrument flight rules flight plans under the provisions of 14 CFR Part 121. The 2 pilots, 3 flight attendants, and 120 passengers aboard flight 229 and the 2 pilots, 3 flight attendants and 57 passengers aboard flight 424 were not injured. The flights were originating at the time of the accident, and were en route to San Jose, California and Minneapolis Minnesota respectively. N305UA had completed a straight pushback from gate B19 via a tug and wing walker. The airplane was disconnected from the tug and its engines were running. The pilots received hand signals from the tug operator releasing them from his guidance. N373UA was being pushed back from gate B21 via a tug and wing walker. The wing walker, who was positioned at the front of the right wing, stopped the pushback. The wing walker and tug operator had a brief discussion which resulted in the tug operator pulling the aircraft back toward the gate. The pilots of N305UA visually cleared the area and began to taxi by turning to the west. During the turn, the left wing tip of N305UA struck the right wing tip of N373UA. N373UA was positioned a reported "5 to 10 feet too far west" at the time of the accident. Post-accident inspection by airline maintenance personnel revealed that the left wingtip of N305UA and the right wingtip of N373UA had scratches, dents, and broken navigation lights and lenses. There was no structural damage found to either aircraft.