NTSB Factual Report

On November 6, 2010, about 1430 mountain daylight time, a Cessna T210N, N6179Y, impacted the terrain during a forced landing about 30 miles north of Baggs, Wyoming. The commercial pilot and his passenger were not injured, but the airplane, which was owned and operated by the pilot, sustained substantial damage. The 14 Code of Federal Regulations Part 91 personal cross-country flight, which departed Broken Bow, Nebraska, about two hours prior to the accident, was en route to Brigham City, Utah. The flight was being operated in visual meteorological conditions. No flight plan had been filed.

According to the pilot, while in cruise flight he suddenly heard and felt a solid "thump" that appeared to have come from the area of the engine compartment. Soon thereafter, the oil pressure started to drop and the engine started losing power. About two minutes after the oil pressure started dropping, the engine began making a knocking sound and the propeller began to slow. Eventually the engine stopped producing any power, and the pilot attempted a forced landing on a nearby narrow dirt road. Although the touchdown was successful, the pilot was unable to keep the airplane aligned with the rough and rutted road, and it therefore departed the road surface and went into the nearby rough and uneven terrain. After the airplane encountered the rough terrain, its nose dug in, and it flipped over onto its top.

An on-scene inspection by an Airworthiness Inspector from the Casper Flight Standards District Office (FSDO) determined that there was a hole in the side of the engine crankcase, and that much of the engine oil had escaped through that hole.

The airplane was recovered to the facilities of Beegles Aircraft Service, in Greeley, Colorado, where it underwent a full teardown inspection under the oversight of a Federal Aviation Administration (FAA) Airworthiness Inspector from the Denver FSDO. The teardown included inspection of all engine accessories and external components, and the separation of the two crankcase halves in order to remove and inspect all the internal engine components. No anomalies, contamination, or evidence of malfunction were found in any of the engine accessories, to include the magnetos, ignition harness, sparkplugs, fuel pump, oil pump, fuel manifold valve, fuel injection nozzles, oil cooler, and oil filter. The cylinders, piston, and valve train were all without evidence of anomaly or malfunction.

Upon splitting the crankcase it was determined that all the main journal bearings showed significant wear, with some degree of the underlying copper material showing through; but none of the journals displayed evidence of significant thermal damage. In addition there was no significant thermal damage to any of the crankshaft main journals, and no evidence of hard particle passage on the main journals surfaces. It was noted that the slot that holds the retention tang for one-half of the number two main bearing had elongated, but there was no evidence that the main bearing had shifted, or that the flow of lubricating oil had been interrupted.

An inspection of the crankshaft revealed evidence of severe thermal stress in the area of the number one and number two connection rod journals. Although the crankshaft oil transfer tubes were clear and unrestricted, both connecting rod journals displayed characteristics consistent with heat buildup due to a localized lack of lubrication. Both had turned a light reddish tan color and both were completely void of any lubrication. The number two connecting rod was still attached to its journal, but the large end of the connecting rod, as well as the rod cap retaining bolts, were reddish tan in color and void of lubrication. The number one connecting rod had separated from its journal, and one side of the rod cap was found to be without its retaining bolt. The greatly distorted large end of the connecting rod, as well as the remaining rod cap retaining bolt, was also reddish tan in color and void of lubrication. The castellated nut end of the missing rod cap retaining bolt, along with damaged pieces of connecting rod bearing material, was found in the oil sump. The recovered bolt section, which had fractured and sustained damage in the area of the fracture, did not display any evidence of being exposed to the overheat condition. Due to the damage to the area around the fracture surface on the nut end of the bolt, and due to the fact that the head end of the bolt was not located, the mode of failure of the bolt could not be established.

A review of the aircraft log books revealed that from October 3, 2007, to May 3, 2010, a period of 31 months, the airplane had accumulated a total of 4.0 hours of flight time. During that period of time, there were no annual inspections performed, and there were no entries in the engine log book to indicate that the relevant engine preservation procedures, defined in Teledyne Continental Motors Service Letter SIL99-1, had been complied with. From May 3, 2010, to October 20, 2010, the airplane, then under new ownership, accumulated approximately 242 hours of flight time. The log book review also revealed that at the time of the accident, the engine had accumulated 1,591 hours since its last major overhaul. According to Teledyne Continental Motors Service Letter SIL98-9A, the recommended time between major overhauls for the TSIO-520-R series engine is 1,400 hours. A log book entry also indicated that on October 20, 2010, about two weeks before the accident, the number two and three cylinders were reinstalled after being overhauled due to low compression.

NTSB Probable Cause

The failure of a connecting rod cap retaining bolt during cruise flight, which resulted in a loss of engine power.