Flight Events
A CFR Part 135 cargo flight departed at night under instrument flight rules (IFR) carrying a load of mining equipment. The route traversed remote, mountainous terrain. Approximately two hours after takeoff, while cruising at 12,000 feet mean sea level (msl), the right engine (number 2) and its propeller began to overspeed.
Emergency and Diversion
The captain feathered the number 2 engine and declared an emergency. He initiated a diversion to an alternate destination about 120 miles away in an area of lower terrain. However, the aircraft could not maintain altitude; the single-engine service ceiling with the current load was approximately 8,700 feet. The captain increased power to the number 1 engine, which then began producing banging and coughing noises. He elected to perform an emergency landing at a nearby, remote, military airfield. The airfield was located in mountainous terrain and featured a one-way, daylight-only approach.
Landing Attempt
The captain lowered the landing gear and flaps, then began a visual approach while attempting to keep the runway end identifier lights (REIL) in view. The aircraft encountered severe turbulence, prompting the captain to apply full throttle to the number 1 engine in an attempt to climb. The REIL disappeared from view, and the aircraft collided with snow-covered terrain about two miles west of the airfield. Ground personnel at the airfield reported high winds and blowing snow with limited visibility.
Postcrash Examination
Postcrash examination of the number 2 engine revealed a loss of propeller control system hydraulic oil. The flight at 12,000 feet was conducted without crew oxygen. The crew had exceeded their maximum allowable duty day without adequate crew rest.