Cirrus Design Corp SR22 N426TF accident near Mack, Colorado

Probable cause

A total loss of engine power due to the failure of the engine crankshaft, which resulted from maintenance personnel’s application of insufficient torque on the engine case through bolts.

NTSB analysis

The pilot reported that, while the airplane was in cruise flight, the engine suddenly lost power and then seized. During the subsequent forced landing, the airplane sustained substantial damage. Examination of the engine revealed that the crankshaft was fractured through the cheek extending from the No. 2 main bearing journal to the No. 3 connecting rod journal. The No. 2 main bearings had extruded from their crankcase positions and exhibited mechanical damage. The No. 2 main bearing support displayed signatures consistent with bearing shift. The No. 2 main bearing saddle support and several other bearing saddle supports exhibited fretting, consistent with movement between the engine case halves due to insufficient torque on the case through bolts. Maintenance logbook records showed that the Nos. 1, 2, 3, and 4 cylinders were replaced about 1 1/2 years before the accident. When maintenance personnel replaced those cylinders, they would have had to remove the nuts on the case through bolts because they also serve as hold-down bolts for the cylinders. Based on the evidence, it is likely that maintenance personnel applied insufficient torque on the case through bolts after replacing the cylinders, which led to case movement and ultimately to the No. 2 main bearings shifting and extruding, the crankshaft fracturing, and the engine seizing.

Text from the NTSB. Open the NTSB docket for CEN13LA562 for the full record.