Complex sentence: By the mid- 1960s Aeroflot was carrying a remarkable 60 million passengers per year, and at the height of the 1970s summer seasons was flying 400,000 passengers per day (in comparison Pan Am flew 11 million passengers during the whole of 1970).
Split into simpler sentences: By the mid- 1960s Aeroflot was carrying a remarkable 60 million passengers per year. At the height of the 1970s summer seasons it was flying 400,000 passengers per day (Pan Am flew 11 million passengers during the whole of 1970).