On April 24, 1999, at 1138 central daylight time, a Cessna 177, N3270T, operated and piloted by a private pilot, sustained substantial damage during a forced landing in an uneven grass field near Greencastle, Indiana. The pilot was uninjured and the passenger received minor injury. The pilot stated that he was en route to Lafayette, Indiana, but diverted to Greencastle, Indiana, due to low fuel gauge indications. The personal flight was conducted under 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The flight originated from Lovell Field Airport, Chattanooga, Tennessee, at 0930 eastern daylight time. In a written statement, the pilot listed 48 gallons of 100 low lead fuel onboard at the airplane's departure from Lovell Field Airport. He stated that he checked the Flight Service Station by telephone and performed a complete walkaround. He said that he checked the airplane's oil and fuel and found both full. He said that after takeoff, he climbed the airplane to 4,500 feet and leveled off. He stated that he switched to the left tank and flew for approximately 45 minutes, then switched to the right for approximately 45 minutes, and then switched back to both for 45 minutes. He said that he noticed the fuel gauges read about 1/2 on the left and less than 1/2 on the right. He stated that he realized the airplane was using an excessive amount of fuel or that the gauges were malfunctioning. He said that he decided to stop at Putnam County Airport and check to find the problem. He said that he was monitoring the fuel gauges and was preparing for a straight-in approach to runway 36. He said that the engine was losing power about eight miles from the airport. He stated that he turned on the electric fuel pump, the engine ran a few more seconds, and the engine quit. He said that he could not make the airport and attempted an emergency landing in a wet grass and muddy field. After landing, the right fuel cap was found out of its filler neck area, on top of the right wing, and in the locked position. The pilot stated that if he had been notified of the fuel cap malfunction, the accident could have been prevented. In a written statement, the lineman from the Fixed Base Operator (FBO) at Lovell Field Airport stated that he parked and fueled the accident airplane with the owner at approximately 1830 on April 23, 1999. The lineman said that the right wing fuel cap was not engaged in its filler neck area and that its chain held the cap on the top of the wing. The lineman stated that the right wing had a blue trail down the back of the wing about 8 to 10 inches wide. The lineman said that he told the owner about the cap and told the owner it would be a good idea to "sump" the tank. The lineman noted that the right cap was in the locked position. The lineman stated that after servicing, he installed the cap back in its filler neck area on the right wing. The cap was sent to the Federal Aviation Administration (FAA) in Wichita, Kansas for an examination. FAA and Cessna Aircraft Company investigators observed that the self-locking nut on the bottom of the right fuel cap could be turned by hand. The right cap's interior locking dome was found not seated on the bolt that attached through the cap to the pilot operated locking tab on the cap's exterior face. It was also found that the interior dome could be moved by hand.