Incident Overview
On an unspecified date, a light twin-engine airplane experienced a propeller overspeed on the number two engine while in cruise flight. The pilot, who had 1,430 hours of total flight time, was flying at 5,500 feet mean sea level when he noticed the propellers were "out of sync."
Pilot Actions
The pilot made minor adjustments with the propeller levers to synchronize them, but the propellers remained out of sync. The right propeller began to overspeed by approximately 1,000 RPM, and adjustments with the right propeller lever had no effect. The pilot then retarded the throttle, but could not maintain proper engine RPM. He elected to land at the nearest airport, located about 12 miles away.
During the descent, the pilot noticed the number two engine was starting to overheat. He retarded the throttle again and increased airspeed to aid in cooling. Shortly after, the airplane started to shake, and upon looking outside, the pilot observed the propeller was "wobbling."
Landing
The pilot subsequently executed a forced landing into a muddy wheat field. The airplane had undergone its annual inspection on December 12, 2003, and was determined to be in an un-airworthy condition. A special flight permit for maintenance was issued on April 20, 2004, which was to expire on April 30, 2004.
Propeller Governor Examination
The propeller governors were tested on a governor test stand and functioned normally; however, they were out of specification. The maximum RPM on the left governor was 2,394, and on the right governor was 2,310. The specified RPM is 2,435. The specified feather RPM is 1,700. The left governor achieved 1,671 RPM, and the right governor achieved 1,634 RPM.
Inspection after disassembly was uneventful. Both governors were found to be "old and worn, exhibited similar wear patterns, but were functional."
Conclusion
The reason for the reported propeller overspeed could not be determined.