I have traveled with a Banjo in a hard case. I had no problem storing it case and all in an overhead bin of a B727 and B757. I did take up any space in case with a small hand towel and covered the top with another towel. The strings were well loosened, the cold of flight will make them contract severely. This will provide severe tension to the neck. AS far as the body is concerned it will get cold soaked, just let it warm up by itself naturally. If your worried about humidity or lack of, you could cut up an apple and bury the pieces in the case, It would provide some moisture for the flight.

I dont think your fiddle in its case would be as big a a banjo, I dont see why they would turn you down at the door of the aircraft. Take it with you.

Sailor DAn