I bought a Fender Strat in Savannah Georgia and flew by 3 different air routes to Muscat Oman
After scouring the net for advice I decided to keep this baby in its hard shell case rather than trust the gig bag.
Leg 1: Savanna to Wash DC: US Airlines - this was a small plane which has no room in the overheads. I had to put it through checked baggage. (For anyone who doesn't know - you carry it like hand luggage but you have to hand it over at the plane, they tag it, put it in the hold and you get it back at the destination). Well it was not ideal but it was the only solution and it survived.
Leg 2: DC to London LHR: BA-747 - no problem. Carried it on board. FLight attendant said it was too big for the bins so she took it and put it in a wardrobe.
Leg 3: LHR to Muscat vis Abu Dhabi- BA - 777 - no problem. Same deal as aboove it went in the wardrobe.
Everything arrived AOK and nobody said anything about the size (larger than the current hand-luggage specs)'
I found the aircrews very helpful and they really looked after it when they needed to.
Interestingly on the same DC to LHR flight I met up with a guy who had a bass in a gig-bag! He told me he never had a problem travelling with it like that.
OK maybe we were lucky but I would definitely do it again if I had to.
Good luck to others
Cheers
Craptone