Complex sentence: The new runway is expected to be extended and eventually be turned into a third runway for the airport in future expansion plans which is expected to be ready by 2020, to cope with a growing number of flights.
Split into simpler sentences: The new runway is expected to be extended and eventually be turned into a third runway for the airport in future expansion plans. A third runway is expected to be ready by 2020, to cope with a growing number of flights.