On August 22, 2005, approximately 0835 Pacific daylight time, an American Champion 7KCAB, N7546T, nosed over during a forced landing in an open field about three miles north of Richland, Washington. The private pilot, who was the sole occupant, was not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The local 14 CFR Part 91 personal pleasure flight, which departed Richland about 35 minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed. The ELT, which was activated by the accident sequence, was turned off at the scene. According to the pilot, he had just finished practicing a series of aerobatic maneuvers, and was descending back toward the airport when the engine suddenly quit. He attempted to restart the engine, which momentarily fired, but it did not stay running. The propeller, which initially was windmilling after the power loss, eventually came to a stop, and the pilot was unable to get the engine to rotate by activating the starter. He therefore made a power-off forced landing in a nearby open field. Although the flare and touchdown were uneventful, during the landing roll, the aircraft encountered a pair of eight inch high berms, that appeared to have been created by a bulldozer, and subsequently nosed over onto its back. A post-accident inspection of the aircraft and engine determined that the fitting that attaches the oil pressure gauge line to the engine had come loose, and oil had escaped from the area around the fitting. Further inspection revealed that the loss of oil lead to extensive thermal and mechanical damage to the primary lower end engine components, and that the engine had seized as a result of that damage. A review of the aircraft records did not reveal any recent maintenance in which the oil pressure measuring system would have been expected to have been manipulated.