I haven' yet flown with a folding bike, but I often fly with my full-size road bike. So far I have had no difficulty, other than the oversize bag fee, and sometimes a bicycle surcharge. All of my flights are international, from Asia to America or Europe, but customs and security people have not given me any problems. The only problem is the cost; the over-size bag fee is $150, and the bicycle surcharge is usually another $150. I now avoid the bicycle surcharge by telling the check-in attendant that the case contains photographic equipment. They know it's a bicycle, but they never do anything but smile or wink. When I fly business class or better, they don't even ask what's in the case.