Disclaiming Banner: I do not own ALTA. If I did, I would have one of those neat mopeds.
Poetical
Aang worried some days what would happen when Appa couldn't fly anymore. There was a searing pain whenever he thought of that day, but worse would be new generations of air benders who didn't move. There had to be new airbenders. The world needed freedom and it needed air. The essential things of the world that humans couldn't change or even touch always seemed to balance themselves out. In time, eventually.
Maybe someday the war balloons could move them? It would be a little touch of irony. Rather appropriate actually.