On August 7, 2004, approximately 1400 central daylight time, an Enstrom F-28F single-engine helicopter, N78616, sustained substantial damage during a forced landing following a loss of engine power near De Leon, Texas. The commercial pilot was not injured and the two passengers sustained minor injuries. The helicopter was registered to and operated by Arrowhead Helicopters Incorporated, Kingman, Arizona. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91. The flight departed a field near De Leon, Texas, about 1355. In a written statement, the 9,375-hour pilot stated that he was giving attendees of a local festival 6-7 minute helicopter rides. He departed at 1356 with two passengers, 100 pounds of fuel, and climbed to an altitude of 500 feet above ground level (agl). Shortly after, the engine began firing through the exhaust and began to lose power. The pilot entered an autorotation and prepared to land in a school playground. While maneuvering toward the playground, the engine stopped producing power. During the landing, the helicopter slid forward, the skids collapsed and the main rotor severed the tail boom. The pilot instructed the passengers to exit the helicopter. He then secured the electrical switches, the magnetos, and turned off the fuel shut-off valve before he exited the helicopter. The engine was examined on October 27, 2004, under the supervision of a Safety Board investigator. The examination revealed that when then fuel shut-off valve was turned on, fuel began to drain from the port where the main fuel line attached to the fuel manifold valve. The b-nut, which secured the line to the manifold, was partially attached to the port and was finger loose. The b-nut was then tightened, and the engine was test run on the airframe. It started immediately and ran at various power settings without interruption. According to the pilot, he had removed and reassembled the fuel manifold valve approximately nine hours prior to the accident.