On Wednesday, June 9, 1993, at approximately 1112 central daylight time, a Cessna 172, N6446B, was substantially damaged when it collided with trees following a loss of control on initial climb out from the Canyon Lake, Texas, airport. The airplane, owned and operated by the ATP rated pilot, was departing on a local personal flight. There was no flight plan filed and visual meteorological conditions prevailed. The pilot, the sole occupant, received minor injuries. The pilot stated that during the engine run up, he noticed that one of the doors was not properly secured and he adjusted his seat in order to reach the door. He stated that after securing the door, he readjusted his seat to its original position and took off. He further stated that shortly after liftoff, the seat pin broke and the seat traveled aft. He lost control of the airplane and it subsequently impacted the trees off the left side of the runway in a nose down attitude. The airplane remained suspended in the trees. Examination of the airplane revealed that the seat latching mechanism was intact, as were the seat tracks for the pilot's seat. Examination of the latching holes indicated that they were elongated and scrape marks were found between the holes. The end of the latching pin was worn and rounded. Following the examination, the seat was re-installed and the seat locking mechanism operated normally. A review of the airplane's maintenance records indicated that the recurring seat latch airworthiness directive (AD 87-20-03) had last been performed on January 1, 1991.