The DC-3 departed Edmonton at 11:37 for a flight to Port Radium with refueling stops a Fort Smith and Yellowknife. The aircraft climbed to 9000 feet on a direct route to Fort Smith. At 13:20 the aircraft was about abeam Fort McMurray when it encountered freezing rain. The course was changed to Embarras with the intention of joining the airway and following it as far as Fort Smith. Ice built up rapidly and the aircraft descended to 7000 feet. This altitude could not be maintained, so the crew continued down to 5000 feet, still running through rain squalls. Further altitude was lost and at 4500 feet severe turbulence was encountered. This, together with the accumulation of ice, caused the plane to descend further until it struck trees. The captain closed the throttles and carried out a forced landing. PROBABLE CAUSE: “The aircraft continued its flight into an area of freezing precipitation until the accumulation of ice and severe turbulence resulted in partial loss of control during which the aircraft struck trees.”