What happened
During a flight at 8,000 feet, the aircraft encountered heavy fog and icing. During this period, both engine number three and engine number four ceased functioning. The crew attempted to perform an engine restart procedure, but these efforts failed to restore power.
Following the loss of power, the aircraft became uncontrollable. It descended into a forested region, where it impacted the terrain in a level attitude with no forward momentum. The impact resulted in the total destruction of the aircraft and caused the deaths of all 50 occupants.
Findings
Investigations concluded that the primary factor in the accident was the delayed activation of engine ice-protection systems. Because these systems were not armed in a timely manner while flying through icing conditions, the engines lost power. This loss of power also led to a deficiency in the electrical energy necessary to unfeather the propellers and successfully relight enough engines to sustain controlled flight.