I would do this, except I have no clue how, and it doesnt seem to exist anywhere....
a 1x1 grass lot that acts as an international airport with a extremely high capacity. It would allow for people not to have to put a huge airport for every city tile. I've noticed my cities quickly overdue the the Tram center lately, and the tram center is only a muncipal airport.
Thanks.
I recall such a thing in those old airport packs (thalassicus I think) available at simtropolis. Unfortunately the STEX does not seem to work for me today so I cant find the links ::)