Incident Summary
During cruise at 4,000 feet mean sea level, the engine began to vibrate. The vibration became severe. The pilot reduced throttle, but the roughness persisted. The aircraft was unable to maintain altitude with engine settings of 2,000 RPM and 25 inches of manifold pressure. The pilot executed a forced landing in a corn field. During the landing, the nose landing gear collapsed.
Aircraft Examination
After the incident, the engine was checked and found to be operational. Examination of the propeller assembly revealed that one propeller pin had fractured due to fatigue. On the opposite side, the outer bearing race was rusted and broken, also displaying a fatigue fracture. The lubricant on the bearings and bearing race was dry and caked.
Maintenance History
The last 100-hour inspection was performed 34 hours prior to the incident. The propeller had accumulated 1,084 hours since its last overhaul.