What happened
During an aerial-application flight, the aircraft experienced a loss of engine power while performing a low-altitude turn during field spraying operations. The pilot executed an immediate forced landing into a nearby wheat field. Upon encountering the wheat crop, the aircraft spun and impacted the terrain, resulting in damage to the airplane.
The investigation
The on-site investigation focused on the engine components following the power loss. Investigators determined that the engine crankshaft had fractured and the propeller had separated from the engine. While the aircraft was recovered, the propeller was not located; it is believed to have come to rest in a nearby slough or within a densely wooded area.
Findings
The investigation concluded that the crankshaft fracture and the cracking of the oil slinger flange were caused by an extreme load applied to the front of the engine. This load pushed the engine component aft and offset from the crankshaft centerline. The investigation identified ground impact as the most likely source of this load. This offset load created bending loads on the crankshaft, leading to an overstress fracture. Additionally, the aft-directed loads pushed the crankshaft into the case, causing one side of the oil slinger flange to crack where it was restrained by the engine case. The location of the initial crankshaft fracture was not diametrically opposite the final fracture region, which is consistent with clockwise rotation occurring during the fracture process.