Accident Overview
On March 5, 2010, at approximately 1630 central standard time, a single-engine Beech A36 airplane, registration N2036Y, was substantially damaged during a forced landing following a complete loss of engine power while cruising near Slaton, Texas. The private pilot, who was the sole occupant, sustained minor injuries. The flight was operated under 14 Code of Federal Regulations Part 91 as a personal cross-country trip. Visual meteorological conditions prevailed at the time.
Flight Details
The flight departed Lubbock Preston Smith International Airport (LBB) around 1620, with an intended destination of Dallas Executive Airport (RBD), a distance of about 256 miles. While cruising at 5,500 feet, the pilot reported hearing a loud explosion, after which the left front engine cowling blew open. Shortly thereafter, oil appeared on the windscreen and the engine stopped producing power.
Forced Landing and Impact
The pilot executed a forced landing to a flat, plowed field. During the landing, the airplane's left wing separated upon impact, and the aircraft came to rest in a nose-down but upright position. The pilot was able to exit the airplane unassisted.
Engine Examination
A Federal Aviation Administration inspector at the accident site noted that the engine's number 2 cylinder had separated from the crankcase. The engine, a Teledyne Continental Motors (TCM) IO-550-B-12B (serial number 271728-R), was later examined at TCM in Mobile, Alabama, with oversight by the NTSB investigator-in-charge. The examination revealed fretting wear on all crankcase main bearing surfaces except for number 5. The crankcase cylinder decks exhibited wear patterns consistent with movement between all cylinders and the crankcase. Additionally, the crankcase showed signatures indicating that the number 2 cylinder had rocked back and forth before exiting the case. The number 2 piston-to-crankshaft connecting rod cap was found separated from the connecting rod, and the piston pin had been pulled through the lower section of the piston, suggesting that the connecting rod-to-crankshaft separation was a secondary failure.
Maintenance History
According to the engine logbook, the engine was overhauled on March 29, 2002. At the time of the accident, the engine had accumulated approximately 1,072 hours since major overhaul and 641 hours since a top overhaul. On May 29, 1992, TCM had issued Service Bulletin (SB) M92-9, applicable to all Continental 470, 520, and 550 series engines. The SB instructed that at overhaul or when necessary, a 12-point nut must be used and torqued to 790–810 inch-pounds. The accident engine was equipped with the earlier 6-point nuts, which had a required torque of 690–710 inch-pounds. This nut is used on the crankcase through bolts and to secure the cylinders to the crankcase. The SB was not mandatory for the accident flight since it was operating under Part 91.