Stinson 108 1 N8848K accident near Lodi, California

Probable cause

The fatigue failure of the crankshaft, which resulted in a total loss of engine power and subsequent forced landing.

NTSB analysis

The pilot reported that, shortly after takeoff, the engine began to sputter and that it eventually lost all power. The pilot was unable to return to the airport and initiated a forced landing to an open field. During the landing, the airplane struck a berm, nosed over, and then came to rest inverted.

A postaccident examination of the engine revealed that the crankshaft and camshaft had broken adjacent to the accessory section. A metallurgical examination of the crankshaft fracture surfaces revealed a thumbnail-shaped pattern consistent with fatigue that had initiated at the crankshaft surface near the edge of the No. 2 connecting rod journal. It is possible that the fatigue initiated due to the No. 2 connecting rod bearing shifting during operation. The camshaft fracture features were consistent with overstress. Maintenance records indicated that the last annual inspection was completed about 9 months before the accident and that, at that time, the engine had accumulated about 250 hours since major overhaul.

Text from the NTSB. Open the NTSB docket for WPR14LA079 for the full record.