On December 30, 1996, about 1530 central standard time, a Cessna 310Q, N7561Q, landed hard at the Craig Field Airport, Selma, Alabama. The airplane was operated by the pilot under the provisions of Title 14 CFR Part 91, and visual flight rules. Visual meteorological conditions prevailed. An instrument flight plan had been filed via radio, but had not been activated. There were no injuries to the commercial pilot nor his three passengers, and the airplane was substantially damaged. Origination of the flight was Montgomery, Alabama, about 1500, on the same day. The pilot reported that they had stopped at Montgomery for lunch. After departing Montgomery, he air-filed an instrument flight plan. Afterwards, he realized that his charts were all in a wing locker, therefore, he elected to land at Selma to retrieve them. He stated that once over the runway, about 15 feet above the pavement, as he flared, his seat back broke, followed by the hard landing. Subsequent examination of the seat back showed that it was assembled incorrectly which led to its failure on final approach. It was noted that the seat had been connected using a full thread bolt which caused excessive wear on the seat's attaching points. The correct bolt, washers, spacers, and nut should have been used as per the manufacturer's recommendations. It also appeared that a die grinder was used to remove the original seat weakening the metal in the seat frame.