Complex sentence: From 1954 the airline was forced to only operate domestic scheduled flights, where it used de Havilland Herons, although it retained an international charter service using the DC-3 and DC-6.
Split into simpler sentences: From 1954 the airline was forced to operate all its scheduled flights domestically, where it used de Havilland Herons. Braathens SAFE retained an international charter service using the DC-3 and DC-6.