I might just have him bring a note along that explains that he has autism... not necessarily from a doctor.

On the otherhand, if the MD will write one, he could always have it in reserve.

Start without any letter and see what they do. If he needs it, pull out the generic letter of explanation and if they refuse that, then pull out the MD letter.

Let the TSA ratchet up the necessary information, otherwise you'll never know what would be bare minimum.

Good luck. My sister's retarded and is apt to say things like "no guns in there". It's pretty obvious that she's retarded, but still a couple of times the TSAs have said, "WHAT?"

But then I accompany her when she travels so it's a different dynamic..

Rita