I too was very very worried about flying my my DS ASD. I had so many nightmares; my DS causing an emregency landing and being kick off the plane... DS not wanting to go back on the plane on the way back from Disney and having to rent a car to drive home (I even price the trip $$$)...
He was 5 at the time so I read him books about flying. Drove to the airport to show him the planes taking off.
Youtube is also great tool to prepare and show the kids many type of event (plane, rides, show, restaurents, show, etc).
The morning of our departure was great he got dress in a millisecond (every other day I have to help him...) He was excited
The airport security (leaving Canada) I didn't really like as he got a little scared and was hanging on to me. I asked if I could walk throught with him espacially since he is a runner and doesn't listen to commands. Beside my husband was busy with the our 2 other DSs (DH and I got separated in the lines) . She refused

he had to go by himself me first I was told leaving him behind by himself

Well lets just say that it didn't go so well...
The plane ride was AMAZING

He was great, sat by the window. We had some snacks, toys and I bought him a Gameboy for the occasion. When we landed he said "time to go home". He thought the vacation was over

Then he said "hey, where did all the snow go?"
On the way back the lines for security was very very long and the boys were very tired. I was worried that they were all on the verge of a metdown. I approach a TSA agent and asked if there was a quiet area we could wait our turn. He waited there a couple of minutes and he came back and opened a line for us and passed us throught security. I was even allowed to hold him throught the metal detector. I always found the US more acceptable and respectable of people of different abilities.
It was so great that ever since then we have been every year. Next year we are trying a
Disney cruise for the first time
I wish you the best of luck and a magical vacation
