Hello. I'm new here.
Ah yes, Air TV , the ending in itself is left much to the viewer's intepretation as the show itself is filled with symbolism of many sorts. Any ways Air TV was the anime that made me hooked into anime indefinitely. Since many has posted their thoughts on the ending I guess the least I could do is to post a link that helped me answer some of the similar questions I had too after watching the anime.
http://cupped-expressions.net/air/
Sorry if it is very old, and please do remember that this is also one of many ways to interpret the show...^_^