Complex sentence: First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising, and secondly, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate.
Split into simpler sentences: First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising. And second, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate.