Accident Narrative
The airplane collided with mountainous terrain after the flight crew terminated the instrument approach and proceeded visually at night. Prior to takeoff, the flight crew failed to brief or review the instrument approach procedure. During the approach, they exhibited various cognitive task deficiencies.
Cognitive Task Deficiencies
These cognitive task deficiencies included selection of the wrong frequency for pilot controlled lighting, concluding that the airport was obscured by clouds despite weather information to the contrary, stating inaccurate information regarding instrument approach headings and descent altitudes, and descending below appropriate altitudes during the approach. This resulted in the crew's lack of awareness regarding terrain in the approach path.
Visual Illusion Considerations
Pilots approaching a runway over a dark featureless terrain may experience an illusion that the airplane is at a higher altitude than it actually is. In response to this illusion, referred to as the featureless terrain illusion or black hole phenomenon, a pilot may fly a lower than normal approach potentially compromising terrain clearance requirements. The dark visual scene on the approach path and the absence of a visual glideslope indicator were conducive to producing a false perception that the airplane was at a higher altitude.
Ground Proximity Warning and Fatigue Assessment
A ground proximity warning device may have alerted the crew prior to impact. However, the amount of advanced warning that may have been provided by such a device was not determined. Although the flight crew's performance was consistent with fatigue-related impairment, based on available information, the Safety Board staff was unable to determine to what extent the cognitive task deficiencies exhibited by the flight crew were attributable to fatigue and decreased alertness.