NTSB Identification: FTW04LA113.
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Accident occurred Tuesday, April 20, 2004 in Sweetwater, TX
Probable Cause Approval Date: 09/01/2004
Aircraft: Piper PA-23-250, registration: N6257H
Injuries: 2 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
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.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The propeller overspeed for undetermined reasons. A contributing factor was the lack of suitable terrain for the forced landing. Full narrative available
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