Bots are simply too easy to play against. The floorplan can be confusing, and the fact that it is quite easy to mistake a window for an entrance doesn't help this fact. Eventually you will learn. Just keep running around and eventually you'll find your way to where you'd like to be. There apparently is an airduct system in place around the airport, but I still cannot figure out how in the world to get in there.
Defense is hard and easy at the same time.
Basically all the defending team has to do is sit and crowd the plane, while the attackers do all the work trying to actually get to the runway. Keep the attackers out of the cockpit, and they can't win. The rest of the objectives are so spread out amid the airport that it's hardly worth defending them at all. Just sit in the plane, ready your flak cannon, and gib anyone who walks through the door. The attackers are the workhorses of the map.