I really like my SKB Bass Safe, which I've used on countless international and domestic flights during the last several years with no problems whatsoever. I used to always carry a bass on board, but you can't always depend on that being possible anymore because there are a significant number of newer planes in use that have smaller overheads.
Plusses:
You can use any bass as long as the gig bag fits - you're not restricted to a certain type like you would be with a form-fitting case
You can remove the bass and carry it around in the gig bag when you arrive at your destination (i.e. if you want to take the bass to your hotel between sound check and gig)
Lightweight
Wheels
Pretty damn durable
Has good quality, TSA compliant combo lock
Affordable ($150 new at present)
Minuses:
Not every gig bag will fit in it - you need one that is kind of on the thinner side. I have a Levy's bag which I use with it that is fairly durable.
The gig bag will move around a little bit inside the case, but not enough to be a serious issue. I sometimes wedge a strap or other object inside to help with that.
The strap holding the lock in place could probably be cut with a saw or carpet shears, but I suppose any case can be broken into if someone is determined enough.
Not quite as bulletproof as an ATA case, but I think you would need to run over it with a truck or drop it off a high building to do significant damage.
You probably know this already, but I think it's a good idea to detune the bass a bit before you check it to decrease tension on the neck. I don't always do that, but it might be a good precaution.
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