On May 5, 2001, about 1500 eastern daylight time, a Cessna 150J, N51104, was substantially damaged during a forced landing near Osceola Mills, Pennsylvania. The certificated private pilot and passenger received minor injuries. Visual meteorological conditions prevailed for the local flight. No flight plan had been filed for the personal flight that was conducted under 14 CFR Part 91. According to inspectors from the Federal Aviation Administration (FAA), the pilot had departed Sankey Airport, Osceola Mills, about 1 1/2 hours earlier. He had been cruising about 6,500 feet, with the mixture leaned, and was returning to the airport. As he neared the airport, he retarded the power, placed the mixture control in the rich position, and initiated a descent. As the airplane descended through 3,000 feet, the engine began to run rough. The pilot added carburetor heat; however, the roughness continued. The pilot performed a forced landing in an open field with rolling terrain. The airplane touched down on rising terrain, and the nosewheel dug into the ground. The airplane nosed over and came to rest inverted. Both wings and the fuselage were wrinkled. The FAA inspectors also reported their examination of the airplane revealed fuel in the tanks, in the fuel line leading to the carburetor, and in the carburetor. The lower spark plugs on the right side of the engine were sooty in appearance. Witnesses reported the engine was sputtering as the airplane descended, and black smoke was observed coming from the engine exhaust. Further, in a written report, they stated: "On May 22, 2001, the continued investigation of N51104's engine problems revealed; Cylinders # 1 & 3 top spark plugs and cylinder # 4 top and bottom plugs to have a black sooty appearance; cylinder # 2 top and bottom spark plugs were covered with oil. The exhaust valve in cylinder # 2 was found stuck in the open position, all other valves opened and closed when the engine was rotated. All push rods and rocker arms moved normally when the engine was rotated...." The pilot had not received a flight review within the preceding 24 calendar months.