I would not risk taking my daughter on an airplane (or lots of places actually) unless I was reasonably certain she and I could handle it, even then something can come up at anytime...I just don't see a way to do it that would work and being that every single autistic person has different and often mysterious (to the rest of us) triggers, I don't even see how you could train somebody to not make it worse. I can see how just air pressure changes could make it worse for my child, and nobody could do anything about that. Or maybe the sound of another passenger's voice or the sound of the pilot speaking on the intercom....there are just too many variables. The only thing I can think that might possibly help would be to have flight simulation sessions with the individual beforehand until they become habituated enough to handle the experience....but you know the cost of that would have to come from somewhere....