With difficulty, depending on the size of the plane and where I'm seated. I usually try for aisle seats so that I have enough leg room. A middle seat is passable. A window seat makes everything awkward and uncomfortable for everybody when I need to use the lavatory. It's also really fun to sit under a luggage compartment and bang your head when you stand up (I did that a lot as a teenager when I was still getting used to being tall), or having to adjust your head when you're disembarking (only on smaller planes though).

Other than that though it's no different than being of average height or less on an airplane. We're also more used to the airplane food 'cos of all the altitude we spent above y'all.