On September 19, 2010, about 1325 eastern daylight time, a Navion G, N2448T, owned and operated by an airline transport pilot (ATP), was substantially damaged during a forced landing to a field, following a loss of engine power in cruise flight near Dublin, Georgia. The certificated ATP incurred minor injuries and the passenger was not injured. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the planned flight to Cannon Creek Airpark (15FL), Lake City, Florida. The flight originated from Evansville Regional Airport (EVV), Evansville, Indiana. The pilot reported that the airplane was in cruise flight at 7,000 feet mean sea level, when the engine began to run rough and the oil pressure decreased. He informed air traffic control, and the controller provided a vector for the nearest suitable airport, W H "Bud" Barron Airport (DBN), Dublin, Georgia; however, the pilot was unable to fly the airplane to the airport. He subsequently performed a gear-up forced landing to a field, located about 6 miles southeast of DBN. During the landing, the airplane struck a ditch and came to rest upright, which resulted in substantial damage to the empennage. The pilot, age 78, held an ATP certificate with type ratings in multiple transport category airplanes. The pilot also held a mechanic certificate. His most recent Federal Aviation Administration (FAA) third-class medical certificate was issued on July 1, 2009. The pilot reported a total flight experience of 18,763 hours; of which, 720 hours were in the same make and model as the accident airplane. The airplane was equipped with a Teledyne Continental Motors IO-520-BA, 285-horsepower engine. The airplane's most recent annual inspection was completed on April 8, 2010. At that time, the engine had accumulated about 469 hours since major overhaul. The airplane had flown about 25 hours from the time of the most recent annual inspection, until the accident. The pilot further stated that sometime after the annual inspection in April, but before a recent trip to Pennsylvania, he changed the oil in the accident airplane. He could not remember what date he changed the oil, and he forgot to record the oil change in the aircraft logbooks. An FAA inspector noted that the No. 5 cylinder was cracked at the base. He also observed no oil on the dipstick, but significant amounts of oil on the engine cowling. When the engine was recovered from the field, an oil drain tube remained attached to the oil quick-release drain plug, and oil was leaking down the side of the oil drain tube. The engine subsequently underwent a teardown examination at the manufacturer's facility, under the supervision of an NTSB investigator. The examination revealed several cracks in the engine case at the No. 5 cylinder base. The case was pushed out, consistent with impact from a loose connecting rod. Disassembly of the engine revealed evidence of thermal distress on the crankshaft at the No. 4 and No. 5 connecting rods, and evidence of lack of lubrication. Less than 2 quarts of oil were recovered from the 12-quart-capacity engine. The No. 5 connecting rod was fractured at the crankshaft attachment points and the attachment fittings were loose in the oil pan.