Why does this locative case end in у and not і?
Airport is a special word that is different, they mention it in the overview. (But I had forgotten also)
You can say both but аеропорту is more natural. Check the tips and notes to see more.
locative for masculine nouns is a topic with such difficult rules, that the dicitionaries usually mention which ending to use :) It's easier to just remember it
Even if the must natural expression is "хто в аеропорту " is "хто на аеропорту" so strange it would not be used?
It is strange, I've never actually heard anyone saying that