I fly a lot. I don't always take a bass with me, but I often do. I've got an anvil flight case that I picked up cheap but have only used once because it's so heavy- it also is a beast to fit in a rental car. I've got some fly in dates coming up this year, and I'm planning on only using it for that type of thing. I also have a branded/fitted standard hardshell cases for most of my 6 basses but I'd NEVER check one of those on an airplane, they're for trailer/back of the van travel.
All of the times I've flown with my basses in the last 4 years I've carried on a bass in a Levy's Leather gig bag. I KNOW I'm taking a chance, but it's a calculated chance.
1- I'm POLITE, and don't expect the airline to cater to me.
2- I've gained status with and airline and I stick with them.
3- I'm EARLY to check in at the airport and at the gate.
4- I keep my gig bag as small as possible. Just the bass in a very form fitting, but well padded bag. I also carry the bass neck pointed down, parallel to my body. This way the neck isn't sticking up over my head, and the bottom of the bag is even with my shoulder. I'm not trying to sneak it on board, but I'm not drawing attention to it either.
5- My bass is my only carry on. My clothes and other things get checked. I MAY have a messenger bag with a laptop, but not always, and it goes under my feet. Also- I either sit in select seating in the very front or in the VERY last row. If I'm the first on the plane and it's already stowed, someone may grumble, but it's first come first serve... if I'm in the very back, and someone is still looking for overhead space, they're already SooL.
6- If all else fails, I keep a copy of FAA Modernization and Reform Act of 2012 Section 403 printed in a plastic sleeve in the pocket of my gig bag.
7- Did I mention I'm Polite?
8- I'm also lucky.
Most of the trips I've carried on have been personal trips, no gigs on the other end, other than jamming with friends. If something happened, I'd be heart broken, but I'd look at it as an opportunity finally get the 55-94 I want but can't justify. BUT- when there's a gig on the other end of the runway... I'm carrying my backup on as above and the primary is going in the anvil and getting checked.
I LOVE my Levy's bag, but If I didn't already have it, and 3/4 of it weren't paid for with a gift card from a generous friend 12 years ago, I wouldn't spend the $400 they're asking for them now. The Reunion Blues Continental and Aero bags are pretty darn amazing for stiffness, protection and style, of the two, I like the Aero a little better because it is smaller and takes up less space in an overhead. I know 3 bassists that have carried on in Aeros and had no problems.