What happened
A CFR Part 135 cargo flight, transporting mining equipment, departed at night on an IFR flight path over remote, mountainous terrain. Approximately two hours into the flight, while cruising at 12,000 feet MSL, the aircraft's right engine (#2) and propeller began to overspeed. In response, the captain feathered the #2 engine and declared an emergency.
The pilot attempted to divert to an alternate destination located approximately 120 miles away in an area of lower terrain. However, due to the aircraft's weight, the single-engine service ceiling was only about 8,700 feet, preventing the aircraft from maintaining its altitude. As the captain increased power to the #1 engine, that engine began producing banging and coughing noises.
The crew decided to perform an emergency landing at a nearby, remote military airfield. This airfield featured a one-way, daylight-only approach situated in mountainous terrain. During the visual approach, while attempting to keep the runway end identifier lights (REIL) in sight, the aircraft encountered severe turbulence. The captain applied full throttle to the #1 engine in an attempt to climb, but the REIL disappeared from view. The aircraft subsequently collided with snow-covered terrain approximately two miles west of the airfield. Ground personnel at the time reported high winds and blowing snow with limited visibility.
The investigation
A post-crash examination of the #2 engine revealed a loss of hydraulic oil within the propeller control system.