My Bike Friday has been on numerous flights since I bought it in '94. It fits in an 'airline-legal' suitcase (L+W+H <=62"), so I take it as one piece of checked baggage and it's almost always been free so far. The suitcase also holds a trailer frame so when I reach the destination I take the bike/trailer parts out, assemble/unfold, put my carry-on bag inside the suitcase on the trailer, and ride out of the airport.