On October 19, 2014, about 1805 eastern daylight time, a Cessna 172K airplane, N79534, was substantially damaged during a loss of control on takeoff at the Greene County-Lewis A. Jackson Regional Airport (I19), near Xenia, Ohio. The pilot, who was the sole occupant, received serious injuries. The aircraft was registered to and operated by MacAir Aviation LLC under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which was not on a flight plan. The local flight was originating at the time of the accident. The pilot reported that during takeoff, about the time that he was rotating for takeoff, the seat unexpectedly slid rearward and the seat back tipped aft. This resulted in his inadvertent application of rearward yoke, his inability to reach the rudder pedals, and the subsequent loss of control. The airplane went off the left side of the runway and struck a ditch bank, resulting in substantial damage to the airplane. Aircraft records showed that on the day before the accident, a different pilot had entered a maintenance discrepancy with a notation that the "left seat slid back three times during flight". On the following day, prior to the accident flight, a mechanic made a repair to the hold-down spring and returned the airplane to service. After that repair and prior to the accident flight another maintenance discrepancy was noted by another different pilot that the "left front seat was in the reclined position and would not lock in the upright position". Records showed that discrepancy had not been corrected before the accident flight. It was undetermined whether or not the accident pilot was aware of those previous discrepancy reports. Postaccident examination of the airplane revealed that a metal tang adjacent to the forward outboard seat track roller had deformed. The tang was part of the seat base and the formed lip retained the seat base to the T-shaped seat track. The deformation was consistent with lateral deformation due to a sideways force. It was not possible to determine if the deformation would have been present during the examination required by the AD. The forward outboard position of the base also retained the pin mechanism that allowed for fore-aft adjustment of the seat position. The pin engaged holes in the track to lock the fore/aft position of the seat. Postaccident examination also showed that the pilot's seat back structure could not be locked in any position. No determination was made as to why the seat back would not lock. The seat mechanism in the accident airplane was the subject of an Airworthiness Directive (AD) AD 2011-10-09, implemented by the Federal Aviation Administration to prevent seat slippage or the seat roller housing from departing the seat rail. The AD stated that such a failure could cause the pilot/copilot to be unable to reach all the controls and lead to the pilot/copilot losing control of the airplane. The AD instituted repetitive inspections of the seat mechanism to prevent such occurrences. One of the items to be inspected was the tang length from the inner edge of the tang to the outer edge (the bend area) of the roller housing. The AD specified a minimum tang length that would affect the width of the opening between the outer and inner tangs. Review of an airworthiness directive compliance sheet for the accident airplane confirmed that the inspections detailed in the AD had been complied with within the required time frame.