We flew from Seattle to Prague with an uncoupled tandem, and only paid $75 in fees for the round trip. It really depends on the airline. We built a wooden box for our tandem. We stripped it and essentially only had the frame and wheels in the box. All the parts went into another suitcase, but a lot of that was because we were up against a weight limit. Still it was easy to do and good to travel with. No damage. I put casters on the box and we piled all our luggage on it for moving about in airports. The box went as oversized sports equipment. Sports equipment can be a much more lenient category than oversized baggage, though it is still checked in the same manner as oversized. If your arrival and departure hotels are the same, the hotel will store the box for you if you make arrangements in advance.