Since it is a short flight, if you think your child can sit still I would go without the carseat. I have a 3 and a 1 year old and we have been taking short flights with our 3 year old without a carseat since she was about two and a half. Here's why: most airlines no longer allow preboarding for families, so trying to get on board gatechecking a double stroller, carrying two carseats, two children, a diaper bag, snacks, toys, etc. with all of coach class is near impossible. Also, depending on the type of airplane, you may have difficulty installing the carseat (airplane seat width varies) even if it is FAA approved. I've found that with our carseat my daughter is too high up for the tray to come down all the way and therefore rests at a slant causing snacks and crayons to roll all over the floor. In her carseat she is also able to put her feet up on the back of the chair in front of her and push, kicking the other person and to her it becomes a game, to everyone else involved, it's annoying.
Since we ditched the carseat, flights have become more relaxing. We have the "big girl" talk, she knows she has to keep her seatbelt on just like mommy and daddy and snacks and crayons don't roll around the plane... as much.
For us, the flight to Orlando is just under an hour and for my daughter flying without the carseat works for us. For that amount of time she enjoys quiet activities and we have had no problems keeping her in her seat. My younger daughter...well that's a whole other story...
Do what you think is best. This is what works for us.