You can have the best and most expensive case in the world. If it's opened and the instrument is damaged then, that's the problem. Patitucci's bass was damaged after it's case was opened, possibly by security people. Steve Lawson's one Modulus bass was irreparably damaged about 6 or 7 years ago, again possibly after the case was opened by security people, his case was undamaged.
I've got a Mono bag, personally I wouldn't want someone's heavy suitcase being stuck on top of it in a luggage hold. It's a great gig bag, and extremely well padded, but it's not robust enough in my opinion to protect an instrument during transit in a luggage hold of an aircraft.
A far better idea is to phone the airline beforehand and ask.