History of Flight
On August 14, 2011, about 1600 Pacific daylight time, a Beech B36TC, registration N6465X, experienced a total loss of engine power during cruise flight at 10,500 feet mean sea level. The pilot detected a loss of engine power followed by a complete loss of all power. According to the pilot, he observed 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 but was unable to reach the runway, instead landing in a field south of runway 32L. The private pilot and two passengers were not injured, but the airplane sustained substantial damage to the right wing and fuselage. The cross-country personal flight had departed Bermuda Dunes, California, about 1430, with a planned destination of Byron, California. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed.
An inspector from the Federal Aviation Administration Flight Standards District Office in Fresno, California, responded to the accident site. Preliminary investigation revealed that the number 4 cylinder and piston were missing from the engine.
Aircraft Information
The airplane was a Beech B36TC, serial number EA-306. A review of the airplane’s logbooks showed a total airframe time of 2,322.0 hours at the last annual inspection, which was dated August 11, 2010. The Hobbs hour meter read 1,592.2 hours at that inspection and 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, with 39.4 hours since major overhaul. 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 protrude 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, and rubbed and displaced material was noted on the cylinder attachment area.
Three deck studs remained attached and had minor damage to their threads. The number 4 cylinder upper through-bolt separated 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 revealed that all had 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.