It's not a safe thing to assume that you will get a bass guitar in a soft bag onto a plane anymore.
Many have had good luck with the SKB Roller Case for Bass. It's a hard outer shell with wheels and a handle. You put your bass in its gig bag (which acts as padding) into the shell, and then you check it through. It's very rigid, and it is a breeze to wheel around. Just over $100.
The coolest thing is that once you get to your destination, you have your gig bag versus some huge, heavy road case. Nice! The only downside that I found with this case is that the fit is quite tight with a gig bag, so you need to empty the outer pockets and carry your tuner, cables, strap, etc. in your luggage.
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