On December 14, 2003, approximately 1245 central standard time, a Cessna 210 single-engine airplane, N718LG, was destroyed when it impacted the terrain during a forced landing following a loss of engine power during cruise flight near Clarendon, Texas. The private pilot sustained minor injuries, and the private pilot-rated passenger sustained serious injuries. The airplane was registered to the Cole 1st Family Ltd. Partnership, Amarillo, Texas, and was operated by the pilot and passenger. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The cross-country flight departed Addison Airport, near Addison, Texas, at 1021, and was destined for the Tradewind Airport, near Amarillo, Texas. According to the pilot, while in cruise flight at 8,000 feet, smoke was observed emanating from the engine cowling and entering the cockpit. The pilot then shut down and secured the engine, and initiated a forced landing to flat terrain. During the forced landing, the airplane touched down in a field, impacted and proceeded through a fence. The left wing then struck a scrub tree, the airplane rotated to the left, and came to rest upright adjacent to a roadway. Examination of the airplane by a Federal Aviation Administration (FAA) inspector, a representative of the airframe manufacturer, and a representative of the engine manufacturer revealed the engine's number six cylinder was partially separated from the engine crankcase. The airplane was recovered to Air Salvage of Dallas, near Lancaster, Texas, for further examination. On January 7, 2004, the airplane was examined by the NTSB investigator-in-charge (IIC) at the facilities of Air Salvage of Dallas. Examination of the airframe revealed no anomalies. Examination of the engine and the number six cylinder revealed five of the six deck studs and one of the two through-bolts had fractured and separated. The cylinder flange was approximately 0.125" off of the crankcase cylinder deck. The engine was removed and shipped to the facilities of Teledyne Continental Motors (TCM), near Mobile, Alabama, for further examination. According to the aircraft maintenance records, at the time of the accident, the engine had accumulated 834.7 hours since overhaul which was completed on March 15, 2001. The most recent engine maintenance recorded was an oil change on December 10, 2003. On January 20, 2004, at TCM, under the supervision of the NTSB IIC, the engine was examined and disassembled. The disassembly revealed one through-bolt was loose, one deck stud was loose, five remaining deck studs were fractured, and one through-bolt was fractured on the number six cylinder. The number six cylinder and crankcase mating surfaces displayed evidence of fretting. No additional anomalies were noted with the engine that would have precluded normal operation. The fractured studs, through-bolts, and the mating surfaces were examined by a TCM metallurgist. According to the TCM metallurgist report, fatigue propagation was noted on three of the fractured deck studs. The fracture locations were approximately at the flange thickness above the cylinder deck. Examination of all fracture surfaces under the scanning electron microscope displayed three studs (1, 2, and 4 o'clock positions) with signatures consistent with fatigue, and the two other studs (5 and 7 o'clock positions) and the through bolt displayed signatures consistent with overload. A witness line, noted on the loose through-bolt located in the 10 o'clock position, was formed from repeated impact with the cylinder flange. Hardness of each of the deck studs and through-bolts met manufacturer's specifications.