NTSB Identification: WPR11LA380
14 CFR Part 91: General Aviation
Accident occurred Sunday, August 14, 2011 in Lemoore, CA
Probable Cause Approval Date: 11/26/2012
Aircraft: BEECH B36TC, registration: N6465X
Injuries: 3 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A loss of engine power during cruise flight due to maintenance personnel's failure to adequately torque the number 4 cylinder retaining nuts, which resulted in the in-flight separation of the cylinder.

Full narrative available

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