Aerial-Application Aircraft Damaged After Engine Power Loss and Forced Landing (N9224R)

Accident Overview

An aerial-application flight experienced a loss of engine power while executing a low-altitude turn during spraying operations. The pilot immediately conducted a forced landing into a nearby wheat field. Upon encountering the wheat crop, the aircraft spun around and impacted terrain, sustaining damage.

Investigation Findings

The on-site investigation determined that the engine crankshaft had fractured and the propeller had separated from the engine. The propeller was never located and is believed to be in a nearby slough or densely wooded area. Examination of the engine revealed that the fracture of the crankshaft and the cracking of the oil slanger flange were the result of an extreme load applied to the front of the engine, pushing aft and offset from the crankshaft centerline. Ground impact is the most likely source of this load. The offset load created bending loads on the crankshaft, leading to an overstress fracture. The aft loads pushed the crankshaft into the case, causing one side of the oil slinger flange to crack as it was restrained by the case. The location of the crankshaft fracture initiation was not diametrically opposite from the final fracture region, consistent with some amount of clockwise rotation (as viewed from the aft) during the fracture event.