I'm flying with my 2 year old twins next week. One has autism. We've flown twice already and she has been good. But I always over prepare. Pinterest has good tips on traveling with toddlers. You can also ask your OT about sensory tips that will help his/her needs. I've been practicing having head phones for the iPad. Lots of crunchy snacks and activities. I'm bringing a bottle with juice for take off and landing. I heard jet blue has a program for a pretend flight for children with special needs, but I haven't looked into it.

Picture schedules really help a lot with my son.

My son flew better as a child than as adult. I took him to the airport several times before the first flight to watch the airplanes. Bought him toy airplanes. He was fascinated. Bought him a special toy that he could have as soon as he sat down in the airplane seat. What worked for one doesn't necessarily work for another, but ideas...

Try one of the faux flights. They just taxi the runway for a half hour. Some airports do one around christmas to see santa