NTSB Identification: ANC97FA024.
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Nonscheduled 14 CFR
Accident occurred Wednesday, January 29, 1997 in SPARREVOHN, AK
Probable Cause Approval Date: 05/21/1998
Aircraft: de Havilland DHC-4A, registration: N702SC
Injuries: 1 Fatal,1 Serious.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The CFR Part 135 cargo flight (flt) departed at night on an IFR flt with a load of mining equipment. Route of flt was over remote/mountainous terrain. About 2 hrs after takeoff, while cruising at 12,000' msl, the right engine (#2 eng) & propeller began to overspeed. The captain (capt) feathered the #2 eng & declared an emergency. He began to divert to an alternate destination, about 120 miles away in an area of lower terrain, but the aircraft (acft) would not maintain altitude (single eng service ceiling, as loaded, was about 8,700'). The capt increased power to the #1 eng, but it began to produce banging & coughing noises. The capt elected to perform an emergency landing at a nearby, remote, military airfield (A/F). The A/F was located in mountainous terrain & had a one-way, daylight only approach. The capt lowered the gear & flaps, & began a visual approach while attempting to keep the runway end identifier lights (REIL) in view. The acft encountered severe turbulence, & the capt applied full throttle to the #1 eng in an attempt to climb. The REIL disappeared from view, & the acft collided with snow covered terrain about 2 miles west of the A/F. Ground personnel at the A/F reported high winds & blowing snow with limited visibility. Postcrash exam of the #2 eng revealed a loss of the propeller control system hydraulic oil. Flt at 12,000' was conducted without crew oxygen. The crew had exceeded their maximum allowable duty day without adequate crew rest.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

loss of the right engine propeller control oil, which led to an overspeed of the right engine and propeller, and necessitated a shut-down of the right engine; and failure of the pilot to maintain adequate altitude/distance from terrain during visual approach for a precautionary landing at an alternate airport. Factors relating to the accident were: fluctuation of the left engine power, premature lowering of the airplane flaps, and an encounter with adverse weather conditions (including high winds, severe turbulence, and white-out conditions) during the approach.

Full narrative available

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