When Allie was @ 8yo, went took a ferry to Catalina Island and back. She loved that, and although I loved the ride, I was very scared she would end up overboard. On a boat though, you can go topside to the open air and walk around quite freely. On a plane your movement is fairly restricted so a completely different environment.

I guess if you absolutely had to fly with an autistic person, you might look into chartering a plane...If there was no way I could drive it, I'd make sure I had plenty of valium, even on a private charter.