hey! I flew to Australia in 2005 and did ok, but I made sure that I had a bunch of Pred with me just in case. I talked to my GI and made a game plan in case I started to flare while I was over there, and he provided me with a prescription of Pred to keep in case of an emergency. So, that's my best advice. Just talk to your doc and make a game plan.
As far as the 16-hour flight over there, I was fine, but I flew on a 747-400 which has a bunch of crappers on it, so there were never really any major lines to wait in. Most people were usually sleeping except around meal times, and then it might have gotten a little busier around the facilities.
In fact, speaking of being stuck in line, I ate a bunch of McNuggets and a chocolate shake right before we boarded the plane for the flight over. I don't know why, I never eat MC D's any more, and I don't even know if it was a UC related reaction, but I can remember standing in line to board and feeling a coup developing in my bowels. It turned into one of those, "My kingdom for a toilet!" moments. So, we finally get to our seats, and I set my bags down and head for the nearest airplane lavatory. On my way, I'm wondering, "does the ground crew even have the toilets prepped when the plane is still sitting at the gate?" But by that point, I didn't even care if I lifted the lid and saw the tarmac below me - I was committed.
So, after my re-creation of a particular scene in "Dumb and Dumber", I exited and no one was in line, thank goodness, as any governor would have declared the lav a disaster area after that storm.
So, get your pred, don't eat mcnuggets, and enjoy your flight and trip!