On March 14, 2018, about 1600 central daylight time, a White Thorpe T-18 airplane, N118RG, impacted a tree and terrain during a forced landing following an inflight loss of engine power near Cleburne, Texas. The pilot sustained serious injuries. The airplane was substantially damaged during the impact. The airplane was registered to and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Day visual meteorological conditions prevailed in the area about the time of the accident, and the flight was not operated on a flight plan. The local flight originated from the Blackwood Airpark, near Cleburne, Texas, at 1545.According to the pilot's accident report, the flight departed to the north from the airport. The engine was running rough while he was flying northbound. The pilot started troubleshooting the roughness and decided to return to return to the airport. He stated, "I mistakenly landed in a pasture, short of the runway, with [the] plane coming to rest after hitting a tree." The pilot reported to the Texas Department of Public Safety Officer at the scene that the fuel line was not feeding through, and later reported to a Federal Aviation Inspector (FAA) that he believed he ran out of fuel. The FAA inspector examined the airplane at the scene. There was no evidence of fuel. The engine had been pulled away from the fuselage. Due to the extent of the damage, the fuel system and engine were not tested. There was no record that an annual inspection of the airplane was conducted recently. The pilot reported the last annual inspection was on May 17, 2011. The pilot reported that he did not have a current flight review and did not know the date of his last medical certificate.