Incident Overview
During cruise flight at 6,500 feet, with a power setting of 2,500 RPM and 21 inches of manifold pressure, the pilot reported an inability to synchronize the left propeller. The propeller then decreased to 1,500 RPM, surged to 3,000 RPM, and dropped back to 1,500 RPM. Attempts to feather the propeller were unsuccessful.
Unable to maintain altitude with power from the right engine, the pilot performed a forced landing on an interstate highway. During the landing roll, the left wing contacted an embankment, causing the aircraft to veer off the side of the interstate. A fire started in the right engine, and the right wing was destroyed.
Post-Accident Inspection
A post-accident inspection of the left propeller failed to reveal any reason for the RPM fluctuation or the inability to feather. Water was found throughout the left engine fuel system. The propellers had been overhauled prior to the flight.
The left propeller governor was bench tested and, although capable of operation, was found to be operating slightly outside its specified operating range.