I'm genuinely curious and it wasn't addressed at all in the post - how did he make his first trip? Wasn't ALL of it novel the first time? Yet subsequent trips ALL of it has to be same or his stress level goes up?
I have a friend whose son is mildly autistic, and each new thing in his life has to be introduced in a specific way. For example, a new shirt will be brought into his room for several days for him to look at and touch. Once he's used to that he'll try it on, but he'll almost immediately take it off for the 'right' shirt that day. This can go on for several weeks, before he'll wear it in the house, but he still won't leave the house without putting on the 'right' shirt. He actually has a job, but it took almost six months from when he was hired until he would wear the full uniform for the job, because each piece of the uniform (and of course the job itself) had to be introduced in this fashion.
My friend's son is only considered 'mildly' autistic. I simply can't image going through a major airport the first time with someone like this. Once the pattern is established, yes, it's a challenge to keep it going ... but what about the first time?