Summary
While en route to apply dry fertilizer to a field, the aircraft's engine made a popping sound followed by a significant loss of power. The pilot determined that the aircraft could not remain airborne and initiated a forced landing in a nearby field.
Incident Details
During the descent, the pilot began dumping the fertilizer load to reduce weight. The aircraft made a successful touchdown on the soft terrain, but shortly after, the main gear sank into the ground. The right main gear leg folded aft, causing the nose and right wing to impact the terrain.
Post-Accident Examination
A post-accident inspection of the engine revealed that the head of the number seven cylinder had fractured circumferentially just above the location where the head screws into the cylinder barrel. Although the head had not separated from the barrel, the fracture extended far enough around the barrel to create a misalignment of the cylinder geometry. This misalignment prevented the intake valve from closing properly. The examination found no indication of detonation or any other anomaly that would have applied greater than normal loads to the cylinder structure.