Incident Overview
A pilot reported that while flying at 10,000 feet mean sea level in intermittent rain, he activated the alternate air system for both engines. The outside air temperature gauge indicated 43 degrees Fahrenheit. Shortly thereafter, the left engine began losing RPM. The pilot chose not to feather the propeller, believing that he was obtaining minimal RPM performance from the engine.
Sequence of Events
As the aircraft descended through 8,000 feet, the temperature gauge read between 39 and 40 degrees Fahrenheit. At that point, the right engine experienced a drop of 200-300 RPM. The pilot subsequently executed an off-airport forced landing with the landing gear retracted.
Post-Accident Examination
Examination of the wreckage revealed that fuel was available on the airplane. The left engine was started during testing and operated uneventfully, performing normally up to a manifold pressure of 25 inches of mercury.