On May 7, 1994, about 1800 eastern daylight time, a Cessna 150M, N704LZ, registered to Apalachicola International Aviation Training Center, collided with terrain near Port Saint Joe, Florida, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The airplane was destroyed by a postcrash fire and the private pilot and one passenger sustained serious injuries. The flight originated about 1730 from the Apalachicola Municipal Airport, Apalachicola, Florida. The flight departed and after the pilot spotted a boat which was beached at the tip of an island, he descended to about 150-200 feet above ground level, overflew the boat, then he initiated a climbing left turn. During the turn the airplane felt "mushy." He rolled wings level, applied full power and reduced the back pressure on the control column but the nose pitched down. During the uncontrolled descent the airplane collided with a sand dune, nosed over, and was destroyed by a postcrash fire. One of the occupants of the boat who was onshore observed the accident and helped with the release of the difficult lapbelt of the passenger. The passengers legs received second and third degree burns as a result of the postcrash fire. Both male ends of the lap belt system for each seat were located but only one of the female ends of the lap belt system for each seat was located. The recovered lap belt components were examined which revealed no evidence of preimpact failure or malfunction. Examination of the airplane by an FAA inspector and by a representative of the aircraft manufacturer revealed no evidence of any flight control preimpact failure or malfunction. The flaps were determined to be extended 39.32 degrees. Full extension is 40 degrees.