Incident Overview
During cruise at 15,000 feet, the flight crew noted that the propeller oil pressure for the left engine had risen above the red line. In response, the crew shut down the engine. The aircraft was over Chattanooga, Tennessee, at the time, and the pilot decided to land at that airport.
Propeller Feathering Attempts
Following the engine shutdown, the flight crew made several unsuccessful attempts to feather the propeller. The propeller eventually stopped rotating at some point before the aircraft exited the runway after landing.
Post-Flight Examination
Inspection of the propeller gearbox revealed that it had seized due to an internal failure. Examination of the propeller control unit showed that the unit had failed to achieve pitchlock, a condition attributed to contaminated oil from the gearbox.
Additional Notes
The aircraft's velocity minimum control with a non-rotating propeller had not been determined for this specific aircraft.