Flight and Conditions
The flight was conducted under an instrument flight rules (IFR) flight plan and was approximately 42 nautical miles from the tower-controlled destination airport when air traffic control cleared the pilot for a visual approach. Dark night visual meteorological conditions prevailed, with an overcast cloud layer at 11,000 feet.
Sequence of Events
After radar service was terminated, the pilot contacted the local control tower. The transmission was garbled and partially unintelligible. Shortly after this transmission, local law enforcement received reports of a downed aircraft. The wreckage was located later that evening approximately 80 feet below the peak of a ridge that rose to an elevation of about 5,700 feet. The initial point of contact with terrain was on the ridge; debris then scattered over the crest and continued down the opposing side in a south-southeast direction toward the airport. The ridge was the highest obstruction between the accident location and the destination airport.
Environmental Factors
The airport is situated in a large valley surrounded by mountainous terrain. At night, clouds and terrain are difficult for pilots to discern, and a gradual loss of visual cues can occur as flight continues toward darker terrain. The horizon is also less visible and distinct at night. The pilot was descending over rural, mountainous terrain that provided few visual ground reference cues. The overcast cloud layer would have prevented moonlight from illuminating the terrain, making it likely that the pilot did not see the rising terrain as the airplane continued toward it.
Aircraft Systems and Examination
The airplane was equipped with an Enhanced Ground Proximity Warning System (EGPWS), but impact damage to the unit precluded postaccident testing. It is unknown how the unit was configured during the flight or what alerts the pilot received prior to impact. Postaccident examination of the wreckage, including both engines, found no evidence of a mechanical malfunction or in-flight structural failure before impact.
Probable Cause
The official probable cause is the pilot's failure to maintain an adequate altitude and descent rate during a night visual approach. Dark night conditions and mountainous terrain were factors in the accident.