Just right away, boats are also ruled out, because we need to get there fast. So, my MCs, Simon, Jon, and Emmett, need to get from New York to an unknown location in England quickly. They can't use any airports because they are being hunted by both the police and a group of (kinda)immortal warriors lead by Simon's nemesis. Earlier threads on this story are here: https://www.writingforums.org/threads/what-could-cause-a-god-to-be-banished-from-his-own-realm.157744/ https://www.writingforums.org/threads/reward-for-a-ghost.158075/#post-1680726 https://www.writingforums.org/threads/hidden-treasure-clue-to-obvious.158103/
Is budget an issue? And do you mean no large commercial airports, or any airports at all? No airport at all would seem to limit you to helicopters or float planes. It's 3 500 miles from NYC to London, which is well out of range of helicopters according to http://www.helistart.com/top-10-longest-range-helicopters.aspx. It's beyond the range of standard float planes as well, but it looks like there are some non-standard models that would get close, at least, like https://en.wikipedia.org/wiki/AVIC_AG600. And unlike planes that require a runway, getting "close" in a seaplane over water isn't disastrous, as long as the seas are calm enough for landing (which is a big 'if'). But if you're just eliminating the large commercial airports, you could find a runway that would take a private jet, and there are lots of those that could handle the range. Most of this would require a fair bit of money and organization, of course...
I too am wondering if you just mean no major airports. My guy used to be a private pilot; at those tiny airports, there is no TSA.
Sometimes, but not right now. Little airports might work, and my MC does have a ton of money to spare.
The first Atlantic crossings were with seaplanes. They required refueling intermediate points like the Azores, but I wouldn't see a problem with a modern seaplane, more fuel-efficient with streamlined floats, doing it non-stop. I don't know if it has been done yet, but I wouldn't be too surprised if I read about it in tomorrow's newspapers. And don't forget balloons. The Double Eagle II went from Maine to France in under six days in 1978, and that was with fairly rudimentary navigational aids. I don't know if that's fast enough for your protagonists, but they'd be extremely difficult to track.
I think you'd be better off with a fast boat than a balloon... this one (http://www.superyachts.com/largest-yachts/fastest-yacht.htm) goes 70 knots, so that'd cross the Atlantic in a bit over two days, right? (1 knot = APPROX 1 mph, so that'd be 3 500 miles / 70 miles per hour = 50 hours).