Hmmm - I haven't had a problem with reels but it has been for domestic travel. Used to carry a 2pc 9ft rod on too, but that was pre 9/11. Better safe than sorry I guess.
Just make sure you carry your flies and other essentials on board if you can. I had BA loose my luggage for 5 days out of a seven day trip to scotland a couple of years ago and it was a lot easier to rent a rod for a day than to go without all of the flies I had tied in anticipation of the trip!