Accident Overview
While cruising in marginal weather conditions at an altitude of 8,500 feet, the airplane struck trees and crashed on the slope of Panther Peak. The aircraft was destroyed, and both crew members were killed.
Flight Path Deviation
At the time of the accident, the crew was not following the assigned route from Burbank to Seattle-Tacoma Airport for an unknown reason. Apparently following a navigation error, the aircraft was 45 miles to the east of its intended route and at an insufficient altitude of 8,500 feet instead of the minimum 14,500 feet required for that segment.
Conclusion
The investigation determined that the airplane deviated significantly from its planned course and was operating below the minimum safe altitude, leading to the collision with terrain. No probable cause was explicitly identified in the official source.