On July 30, 2011, approximately 1000 central daylight time, a Weatherly Aviation Company 620B single-engine airplane, N90181, sustained substantial damage following a loss of engine power while maneuvering near Hettinger, North Dakota. The commercial pilot was not injured. The airplane was registered to and operated by Air Dakota Flite, Hettinger, North Dakota. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 137 aerial application flight. The local flight departed approximately 0950. According to the pilot, while maneuvering at 500 feet above ground level, the engine lost power and oil immediately covered the windscreen. The pilot initiated a forced landing to a road. During the forced landing, the main landing gear collied with a dirt berm on the side of the road, and the airplane entered a ditch. The airplane came to rest upright and the pilot exited the airplane. An examination of the airplane showed the firewall was damaged. A review of the airplane's maintenance records revealed the Pratt & Whitney R-985 AN-14B radial engine (serial number 13084) underwent its most recent annual inspection on July 5, 2011, at a total time of 5,274 hours, and 15.4 hours since major overhaul. At the time of the accident, the engine had accumulated 43 hours since major overhaul. According to the Federal Aviation Administration (FAA) inspector who responded to the accident site, the airplane was involved in an accident in 2009. During that accident, the engine separated from the airframe. After that accident, the engine received a major overhaul that was completed on December 29, 2009. There is no record in the NTSB database regarding an accident involving N90181 in 2009. On October 18, 2011, the engine was examined and disassembled at the facilities of Tulsa Aircraft Engines, Tulsa, Oklahoma, under the supervision of two FAA inspectors. Examination of the engine showed a hole in the side of the number 5 cylinder, which is located at the bottom of the engine. The examination also revealed that several of the connecting rods, including the master rod were broken. The number 5 cylinder is the engine's master rod cylinder. Additionally, there was no evidence in the engine of scoring, thermal damage, or oil starvation. Due to the damage in the engine, the initial failure mode could not be determined.