Each separate airline that you go to and each bike are going to vary. But, in a general sense, most of the time, you should bank on not being able to take your bike as a piece of checked baggage on airlines. Even if you could, to be honest, it is not something that you would necessarily want to take via airlines. During the travel, your bike may end up getting beat up and pushed around during the flight. However, you will most likely never have to make this decision because most folding bikes will still be too large (even when folded). An alternative you could use if you wanted the bike with you is to ship it ahead of time to the location you are traveling to.