I wish they made a flightcase for two guitars. One guitar on one side, the other on the other side. My previous band once got a gig in Italy flying with Alitalia-KLM from Schiphol, the Netherlands. We arrived at the airport with basically two pieces of luggage each, 4 guitars in total, 1 bass guitar, but no more then 30 kilos in total per person. We were then told that only one piece of luggage per person was allowed so we had to pay extra. On the way back we taped some guitar cases together, creating two duals. I doubt that the check in officials at Schiphol would have accepted that but in Italy things were more relaxed. Which was good because otherwise we would have lost money on that gig.
If I had to travel by air again I would opt for a flightcase, preferably one that can carry two guitars, check that in as luggage and carry the remainder of my gear as hand luggage.