WPR11LA380

The pilot reported that, while at cruise altitude, the engine experienced a partial loss of engine power. The pilot requested to land, and then heard a loud noise, followed by the engine cowling opening, and the pilot noted something fly out of the engine compartment followed by a total loss of engine power. Unable to reach the airport, the pilot subsequently made a forced landing in a plowed field. Postaccident examination of the engine revealed that the number 4 cylinder and piston had separated from the engine in flight and likely departed through the open engine cowling. The crankcase had mechanical damage concentrated at the number 4 and 6 cylinder bay areas. The number 4 cylinder bay area had missing crankcase material, with rubbed and displaced material noted on the cylinder attachment area. Further examination of the remaining cylinders found that the retaining self-locking nuts were loose and had not been tightened or properly torqued. Review of maintenance records noted that the engine had been overhauled less than 40 flight hours before the accident. It is likely that maintenance personnel did not properly tighten the self-locking nuts for the number 4 cylinder, which subsequently led to its separation.

HISTORY OF FLIGHT On August 14, 2011, about 1600 Pacific daylight time (PDT), a Beech B36TC, N6465X, made a forced landing in a field following a total loss of engine power near Lemoore, California. The owner/pilot was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot and two passengers were not injured; the airplane sustained substantial damage to the right wing and to the fuselage. The cross-country personal flight departed Bermuda Dunes, California, about 1430, with a planned destination of Byron, California. Visual meteorological conditions prevailed, and a visual flight rules (VFR) flight plan had been filed. The pilot reported that while in cruise flight at 10,500 feet msl, he detected a loss of engine power followed by a total loss of all power. The pilot saw something fly out of the engine compartment when the engine cowling flew open. The pilot declared an emergency and attempted to land at Lemoore Naval Air Station. The pilot was unable to land on the runway but landed on a field south of runway 32L. An inspector from the Federal Aviation Administration Flight Standards District Office, Fresno, California, responded to the accident site. Preliminary investigation revealed that the number 4 cylinder and piston was missing from the engine. AIRCRAFT INFORMATION The airplane was a Beech B36TC, serial number EA-306. A review of the airplane’s logbooks revealed the airplane had a total airframe time of 2,322.0 hours at the last annual inspection. The logbooks contained an entry for an annual inspection dated August 11, 2010. The Hobbs hour meter read 1,592.2 hours at the last inspection. The Hobbs hour meter read 1,603.8 hours at the accident site. The engine was a Continental Motors TSIO-520-UB, serial number 249019. Total time recorded on the engine at the last annual inspection was 1,518.8 hours, and time since major overhaul was 39.4 hours. The engine had undergone a “zero-time equivalent” overhaul on July 14, 2010, by Pacific Continental Engines, Inc., Pacoima, California. TESTS AND RESEARCH Investigators examined the wreckage at National Aviation Logistics in Madera, California, on August 1, 2011. The engine remained attached to the airframe during the inspection. Engine control continuity was obtained from the cabin controls. The number 4 cylinder, piston, and pushrods were not available during the inspection. The cylinder assemblies normally attach to the engine case by eight externally threaded studs mounted to the engine case, which protruded through holes in the base flange of the cylinder assembly, and are secured with self-locking nuts. The crankcase had mechanical damage concentrated at the number 4 and 6 cylinder bay area. The number 4 cylinder bay area had missing crankcase material. Rubbed and displaced material was noted on the cylinder attachment area. Three deck studs remained attached and had minor damage to their threads. The no. 4 cylinder upper through-boltseparated close to the crankcase. The lower through-bolt separated, leaving several exposed threads. Several pieces of cylinder attachment hardware were found in the cowling area. Examination of the cylinder retaining nuts for cylinder numbers; 2, 3, 5, and 6 were found to all have loose self-locking nuts. On November 8, 2011, the missing number 4 cylinder and piston were located 8.4 miles southwest of the accident site in a dirt field.