On July 22, 2020, about 1745 central daylight time, a Vans RV4, N54WP, was substantially damaged when it was involved in an accident near Idabel, Oklahoma. The airline transport pilot and a child passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he was on a multi-leg cross-country flight. On a planned refueling stop at Kennett Memorial Airport (TKX), Kennett, Missouri, the pilot noticed an oil leak coming from a chaffed oil line leading to the propeller governor. The pilot, with assistance from a local fixed base operator mechanic, removed the damaged oil line and replaced the line with a used serviceable oil line. After the installation and preflight, the pilot took off and climbed to 5,500 ft mean sea level, en route to his destination. About 70 minutes later, the pilot smelled something and observed oil on the windscreen. The pilot asked air traffic control for the nearest airport, which was about 11-miles away. As the pilot was maneuvering to the airport to land, the engine stopped producing power. About 1/2 mile from the airport, about 70 ft above the ground, the pilot attempted to maneuver the airplane to land on a roadway. The airplane impacted power lines and the ground. The pilot stated that he could not see the power lines through the oil-covered windscreen. The airplane came to rest in a ditch adjacent to the roadway, resulting in structural damage to the fuselage and empennage. Both occupants exited the airplane uninjured. Examination of the engine after the accident revealed a crack in the oil line leading to the propeller governor from its connection at the engine case. There was no clamp installed to secure the line. The experimental airplane had a conditional airworthiness inspection on May 1, 2020. According to Federal Aviation Administration Airworthiness Directive (AD) 90-04-06R1, a clamp should have been installed on the oil line leading to the propeller governor. The pilot reported that when he replaced the oil line at TKX, there was no clamp present, so he did not install a clamp and was not aware of the applicable AD. He also reported that had he been aware of the AD, he would have installed a new oil line and clamp.