Love all the designs so far. Many are on similar lines that I was planning. I also planned how to start with the simplest operatable airport and slowly expand from there.
Anyway, here is a point that no one has incorporated yet in the designs.
Check in counters like Heathrow T5. As shown here at around 41:20
I guess it would be as simple as keeping 1-2 tile space between the counters for people to pass. For baggage belt, use 1 tile to transition from above ground belt at check in desk to an underground belt running across the back of all the counters.
May not be the best solution for a large number of counters, but should be quite efficient for smaller number.
Then right behind that would be security and then into the secure zone.
@Thorozar, @thetuque, any chance of a rendering of what that may look like?