On September 8, 2000, about 1015 Eastern Daylight Time, a Cessna 172P, N9594L, was substantially damaged during takeoff from Cross Keys Airport (17N), Cross Keys, New Jersey. The certificated commercial pilot sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local personal flight conducted under 14 CFR Part 91. The pilot stated that he was flying from the front right seat, practicing for his certified flight instructor practical test. He initially departed 17N, about 0915. During the takeoff roll, his seat slid rearward. The pilot aborted the takeoff, and locked the seat into position. He then taxied the airplane back and departed uneventfully. The pilot performed some maneuvers, and landed at Millville Municipal Airport (MIV), Millville, New Jersey. He departed MIV uneventfully and landed at 17N, about 1010. He taxied the airplane back to the active runway, and initiated a takeoff roll. During the takeoff roll, his seat slid rearward again. The pilot "...attempted to reach the controls using the yoke. The plane lifted off, stalled, and descended-crashing." A Federal Aviation Administration (FAA) inspector stated that the airplane initially climbed 20-30 feet, then "cartwheeled" along the left wing. It struck two parked airplanes before coming to rest on the airport, and a post crash fire ensued. The inspector examined the holes in the right front seat tracks. He stated the holes were worn and oblong. The airplane had approximately 37 hours of operation since the last 100-hour inspection, performed on August 17, 2000. FAA Airworthiness Directive (AD) 87-20-03 pertains to the make and model accident airplane. The AD requires the seat tracks and seat rollers to be inspected after every 100 hours of operation, in airplanes that are operated for hire.