I fly every year from Frankfurt to Ireland. I used a hardcase and I had to give it to the luggage. And they crashed three times my guitar! One time even the neck was broken! (Fortunatelly it could be repaired) Now I never again give my guitar to the luggage. I take an old guitar (not my 12 string Martin) with me and put it in a soft cover. Then I hope that they have to let me bring the guitar on board.