On February 13, 2002, at 0917 mountain standard time, a Cessna 172S, N299ME, veered off runway 01 during landing and collided on the ground with a taxiing Cessna 172N, N739NS, at Glendale Municipal Airport, Glendale, Arizona. Glendale Aviation LLC was operating both rental airplanes under the provisions of 14 CFR Part 91. The private pilot and one passenger in the landing 172S were not injured; the airplane sustained substantial damage. The certified flight instructor and student pilot in the taxiing 172N were not injured; the airplane sustained substantial damage. The landing 172S departed Glendale on a personal local flight about 0815. Visual meteorological conditions prevailed, and no flight plan had been filed for either airplane. The pilot of the landing 172S submitted a written statement. The pilot said he completed air work in the local practice area and returned for landing. On his first touch-and-go, the airplane veered to the left, but he regained directional control and took off. On the second touch-and-go, the airplane veered to the left again, but he could not recover. The airplane exited the runway about midfield between a taxiway and the high-speed taxiway. It crossed a gravel area between the runway and a parallel taxiway. The instructor and student in the taxiing 172N submitted a written statement. They were taxiing to runway 01 via taxiway alpha. They saw the landing 172S bounce and veer towards the hangars. They stopped and thought the 172S would pass in front of them. However, the landing 172S turned directly towards them. They tried to turn away, but did not have enough time to avoid the collision. The airplanes converged from opposite directions so that the entire leading edge of the left wing of the landing 172S collided with the entire leading edge of the left wing of the taxiing 172N. The left wing tips contacted the left wing roots of the opposing airplane. Both airplanes sustained substantial damage to the wings and fuselage.