On June 30, 1993, at about 1030 eastern daylight time, a Waco ATO, N13918 was substantially damaged during an emergency landing near Alma, Georgia. The airline transport pilot received minor injuries in the accident. The aircraft was being operated under 14 CFR Part 91 by the pilot. Visual meteorological conditions existed at the time of the accident, and no flight plan had been filed for the personal flight. The flight departed Lake City, Florida at 0950, and was enroute to Athens, Georgia at the time of the accident. The pilot reported that during cruise flight, the aircraft engine began to run rough. He attempted to make the Alma Airport, but the engine stopped producing power, and he was forced to attempt an emergency landing in a field. During the landing, in the soft field, the aircraft flipped over onto its back. Personnel who inspected the aircraft after the accident stated that the engine loss of power was a result of a failure of the master rod bearing.