Aaran Stewart does not react well to change.
The 21-year-old has severe autism and obsessive compulsive disorder, but has to negotiate the hectic bustle of Heathrow airport to attend Boston Higashi High School in the US.
To cater for him, staff have attempted to re-create the same conditions every time he flies.
Four times a year for five years, Aaran has met the same airport staff, at the same check-in desk, visiting the same shops, leaving from the same gate on to a plane on which the same seats are reserved.
Speaking to Radio 4's You & Yours at the airport, his mother Amanda said Aaran would not be able to fly if any of the details were different.
She said: "Without the procedure we wouldn't be getting on the plane. It has to be carried out absolutely pristinely otherwise we'll end up with a problem."
The routine includes a visit to shops before heading to the same gate, gate A10. There have been changes, however, as one of the outlets on his route has changed hands.
Mrs Stewart said: "It was an HMV but now it's a Dixons, so he retraced his steps inside as if it was HMV.
"It's routine-based. If there are any delays he'll think you're going to try to change something which will then panic him. When we get to the gate he'll settle.
"Everything's gone to plan, he'll wait for the bus, we've got the seats we need and we're off!"
Mrs Stewart later explained that on arrival the bus did not display the flight number due to a malfunction on the screen, which led to Aaran growing suspicious about its destination.
Fortunately the driver was able to quickly swap buses so he could display BA215 which resulted in Aaran getting on board and making his flight.
Mark Hicks, Head of Passenger Support Services at Heathrow said usually up to 2,500 people with disabilities including reduced mobility will use the airport in a day, from people with visual impairment to older people with reduced mobility.
Asked about whether the general experience of people with disabilities in airports had worsened, he said people notifying them ahead of their arrival did improve service, but the forecasts for the day could occasionally be outstripped by demand.
He added they were striving for a balance which allowed people to retain their ability to travel spontaneously while meeting their needs.
Disability consultant Geoff Adams-Spink said of Aaran's experience: "Hats off to the people who organise it. All too often it's wheelchairs all round and it doesn't matter what your disability is, someone will turn up with a wheelchair and can get quite irritated if you don't sit in it.
"Your rights are governed by EU legislation. The EU has updated its guidelines and you have a right to extra assistance at no cost throughout your journey."