FTW04LA113

The propeller on the number two engine on a light twin-engine airplane experienced an overspeed while in cruise flight. The 1,430-hour pilot reported that while in cruise flight at 5,500 feet msl, he noticed the propellers were "out of sync." The pilot stated that he made minor adjustments with the propeller levers to synchronize the propellers; however, the propellers continued to be "out of sync." The right propeller began to overspeed by approximately 1,000 RPM's, and adjustments with the right prop lever had no effect. The pilot retarded the throttle, but could not maintain proper engine RPM, so he elected to land at the nearest airport, located approximately 12 miles away. The pilot noticed that the number two engine was starting to overheat, so he retarded the throttle again and increased airspeed to aid in cooling. The airplane started to shake, and he looked outside and observed the propeller was "wobbling." Subsequently, the pilot executed a forced landing into a muddy wheat field. The airplane had an annual inspection on December 12, 2003, and was determined to be in an un-airworthy condition. The airplane was given a special flight permit for maintenance, issued on April 20, 2004, which was to expire on April 30, 2004. 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 the maximum RPM 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 RPMs and the right governor achieved 1,634 RPMs. Inspection after disassembly was uneventful. Both governors were found to be "old and worn, exhibited similar wear patterns, but were functional." The reason for the reported propeller overspeed could not be determined.

On April 20, 2004, approximately 1835 central daylight time, a Piper PA-23-250 twin-engine airplane, N6257H, registered to and operated by a private individual, sustained substantial damage during a forced landing following a propeller overspeed while in cruise flight near Sweetwater, Texas. The commercial pilot and the pilot rated passenger were not injured. Visual meteorological conditions prevailed and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 91 ferry flight. The 424-nautical miles cross-country flight originated at 1730, from the Midland International Airport (MAF), near Midland, Texas, and was destined for the Sallisaw Municipal Airport (JSV), near Sallisaw, Oklahoma.

According to the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the 1,430-hour pilot reported that while in cruise flight at 5,500 feet mean sea level (msl), he noticed the propellers were "out of sync." The pilot stated that he made minor adjustments with the prop levers to re-synchronize the propellers; however, the propellers continued to be "out of sync." The right propeller began to overspeed by approximately 1,000 RPM's, and adjustments with the right propeller lever had no effect. The pilot retarded the throttle, but could not maintain proper engine RPM. He elected to land at the nearest airport, located approximately 12 miles away. The pilot noticed the number two engine starting to overheat, so he retarded the throttle again and increased airspeed to aid in cooling. The plane started to shake, and he looked outside and observed the propeller was "wobbling." Subsequently, the pilot executed a forced landing into a muddy wheat field.

Examination of the aircraft by a Federal Aviation Administration (FAA) inspector, who responded to the site of the accident, revealed structural damage to the fuselage. The nose gear and right main gear broke from the fuselage.

A detailed examination and teardown of the propellers and governors was conducted under the supervision of an FAA inspector at Hartzell Propeller Inc., Piqua, Ohio, on June 14, 2004. 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 the maximum RPM 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 RPMs and the right governor achieved 1,634 RPMs. Inspection after disassembly was uneventful. Both governors were "old and worn, exhibited similar wear patterns, but were functional." No anomalies were noted that would have precluded normal operation.

The airplane had an annual inspection on December 12, 2003, and was determined to be in an unairworthy condition. The airplane received a special flight permit for maintenance, issued on April 20, 2004 and was to expire on April 30, 2004.

The reason for the reported propeller overspeed could not be determined.