Beech 35 B33 N8910M accident near Urbana, Indiana

Probable cause

The failure of the crankshaft following several overheating events that had led to a stress crack and the subsequent fracture forward of the No. 6 rod journal.

NTSB analysis

The pilot reported that, while in cruise flight, he noticed a change in the engine sound and a 100-rpm increase on the tachometer. He adjusted the propeller control to lower the rpm, but the rpm immediately increased to over 3,500, which is above the red line. The pilot reduced the propeller and throttle controls, but the propeller continued to overspeed. The propeller then separated from the airplane, and engine oil covered the windscreen. The pilot subsequently made a forced landing to a soft bean field, which resulted in substantial damage to the fuselage, wings, and engine mounts. A postaccident examination of the engine revealed that the crankshaft was fractured forward of the No. 6 rod journal across the oil transfer collar area and that the No. 6 rod had separated from the crankshaft. An examination of the fracture revealed evidence of several overheating events at the surface of the crankshaft next to the oil transfer collar hole. A crack had formed adjacent to the overheated surface, and the surface crack led to a stress crack, which formed the surface of the main separation fracture.

Text from the NTSB. Open the NTSB docket for CEN13LA557 for the full record.