I don't know what the airline rules are, you need to check, but IMHO clipping their wings would be the prudent thing to do. What if, and I always play the worse case scenario, the cage/carrier was accidentally opened somehow during your trip? Your fid would fly away, and it maybe impossible to get them back...in an airport, airplane that has landed with door open. Accidents happen in the flash of an eye.
Clipped wings grow back.......
Kathy