A commercial airport being any airport that has regular scheduled passenger flights.

The mathematics of this question got me thinking: is the network of scheduled flights a single graph?

That is, is there a pair (or triplet or even larger set) of airports such that they only have scheduled flights with each other? Or can you get from any airport to any other?

Ignore vagaries like cargo and general aviation. I'm looking for two airports that I can shuttle between, but would have to drive (or sail) to get to one or the other of them.

Bonus irrelevant question: name the one airport in North American that routinely has more takeoffs than landings (although it's typically not used for passenger flights).