Complex sentence: In 1979 Balair added a DC-10 (call sign HB-IHK), up to that point the fleet was made up of a DC-6, a DC-9 and two DC-8.
Split into simpler sentences: In 1979 Balair added a DC-10 (call sign HB-IHK) to its fleet. Up to then, the fleet was made up of a DC-6, a DC-9 and two DC-8.