Note that you only get the sky ticket the first time you complete the Air Fortress on a character. After that, the instance doesn't give you the ticket anymore on that character. Probably intended (or not) since it has an expiration date and lets you re-reserve the instance and lets you constantly run it over and over again.
Through the use of KP or however WP intends to implement it, you can re enter as much as you want via a 1 hour or 3 hour ticket which is available as well.