On January 24, 2007, about 1300 Pacific standard time, a Ross Hummer Pitts Special, N41HR, nosed over following a loss of control during an aborted takeoff on runway 29L at Stockton Metropolitan Airport, Stockton, California. The commercial pilot, the sole occupant, received minor injuries, and the airplane sustained substantial damage. The airplane was registered to and operated by the pilot. Visual meteorological conditions prevailed for the local personal flight conducted under 14 CFR Part 91, and no flight plan was filed. The flight was originating when the accident occurred. During a telephone interview conducted by the NTSB investigator-in-charge on January 25, 2007, the pilot reported that as he added power on the takeoff roll, the engine rpm increased to 1,800 rpm and then stopped increasing. He decided to abort the takeoff and reduced the power. By this time, the tail wheel was off the ground, and he was using the rudder to steer the airplane. The airplane began to turn to the right, so he applied left brake to stop the turn, and the airplane "tipped upside down." In a written statement, the pilot reported that during the takeoff roll, he "thought there was a slight loss of power." He decided to abort the takeoff and reduced the power. At a speed of about 30 mph, the airplane "suddenly turned sharply as if one of the wheels went into a hole or rut." The pilot applied opposite rudder and brake, but could not stop the turn. The airplane nosed over and came to rest in the inverted position. The pilot stated that the accident was due to "a hole or rut in the pavement or debris such as a piece of aircraft tire." An FAA inspector responded to the accident site. The inspector reported that runway 29L had two grooved depressions running the length of the runway in the asphalt on either side of the centerline. The grooves had a V shape and were about 4 inches wide and 1 inch deep. The width of the grooves corresponded to the width of the tires installed on the main landing gear of the accident airplane.