Engine Seizure and Crankshaft Fracture During Aerial Application Forced Landing (N731SV)

Accident Summary

During the third swath run of an aerial application flight, the pilot reported a sudden loss of engine power. The pilot executed a forced landing, during which the airplane sustained substantial damage. Post-accident examination of the wreckage revealed that the engine had seized and its case was fractured in the vicinity of the number one cylinder. No evidence of preimpact airframe malfunction was discovered.

Engine Examination

Further inspection of the engine disclosed that the crankshaft was fractured forward of the number one connecting rod journal. The investigation concluded that the crankshaft failed due to a fatigue fracture. This fatigue fracture resulted from a misalignment that occurred during a recent overhaul. The misalignment caused damage to the number two crankshaft cheek, which subsequently led to the fatigue failure.

Findings

The engine seizure and case fracture were direct consequences of the crankshaft failure. The forced landing was necessitated by the loss of engine power. The airplane's airframe was intact before impact, with no preexisting malfunctions identified.