Beech N35 N9414Y accident near Warren, Arkansas

Probable cause

The fatigue failure of the engine crankshaft due to oversized crankcase saddle bores, which resulted from maintenance personnel improperly resizing the saddle bores during engine maintenance.

NTSB analysis

The pilot reported that the engine lost power during the initial climb. He then established a glide in an attempt to return to the airport; however, due to "strong" wind, the airplane landed "abruptly short of the runway." A postaccident engine examination revealed that the crankshaft had fractured due to fatigue through the No. 3 cheek immediately aft of the No. 2 main bearing journal. Portions of the saddle bore diameter at the nose of the crankshaft were oversized. The crankcase No. 2 main bearing saddle exhibited longitudinal deformation adjacent to the bore with fretting and galling on the saddle landings. The No. 1 main bearing shells were deformed; the No. 2 main bearing shells were worn, deformed, and partially split. The remaining bearings exhibited helical lines that matched the machining lines on the crankcase main bearing saddles. The tin coating had been worn away except around the oil transfer holes. The appearance of the main bearing shells was consistent with the bearings shifting during operation due to insufficient crush, which was likely caused by the oversized main saddle bore diameters. Maintenance records indicated that the engine was disassembled about 15 months before the accident due to a propeller strike. At that time, maintenance personnel cut the crankcase mating surfaces and resized the saddle bores. The engine had accumulated about 16.5 hours since the engine was reinstalled. It is likely that maintenance personnel improperly resized the saddle bores during the engine maintenance.

Text from the NTSB. Open the NTSB docket for CEN13LA229 for the full record.