Where are you flying from? Which airline? Most airlines will require you either box or bag the bike and will make you sign a waiver in case of damage. Some European and Asian airlines have bike boxes available at the airport, but you take a big risk if they don't have any available when you show up. We've seen accounts here of some European regional airlines that will let you shrink-wrap it (there are shrink-wrapping kiosks available at many airports.) The best solution is to coordinate w/ a bike shop at your city of departure so they'll save you (or you can purchase) another cardboard box, take a taxi to the airport and fly back.