I would guess that the child will be much more comfortable rear facing on a plane due to the angle at which you rearface, which is more reclined, and the fact that he is used to it, and he is not old enough to need to have the plane tray table down. Not to mention if you are using a seat which doesn't fit him on the plane hopefully you have a better seat for any car traveling you will be doing after you get off the plane? I don't mean to sound rude as I don't know your situation but I am trying to help you think of other ideas that may work. If you are concerned about the person in front of you being able to recline (as in several recent news stories) if you mention it to them as they are being seated, and the stewardess can help find someone wiling to switch I would imagine it would not be a big deal.
No problem.
1. A rear facing seat will likely stop the seat in front from reclining, and I'm not getting into a fight with the person in front. this is a 14 hour flight and no on will be OK with that. But more importantly, i want to be able to remove him from the car seat to sleep on the seat (in a belt of course), but the bigger seat won't fit upside down between us and the seat in front.
2. He is MUCH happier sitting up and looking around
3. I will have him slightly reclined for sleeping comfort by using a blanket under the front of the seat to prop it back while reclining his seat in flight.
4. The seat fits him perfectly in weight and height, but the manufacturer's suggestion is one year old, which he's not. It's not MADE for him, but it fits just fine.
5. We are renting a seat at the destination for him and my older son will use this one.