Oh my, another flying my bass thread...
I've flown a few dozen times with an electric bass during the last 3 years. Here is what I believe (YMMV):
1) Get a full ATA road case or one of the SKB "golf bag carrier" style cases if you might possibly ever travel again with a bass, if not, ship it FedEx Air. Not cheap, though, and they put the value of the instrument on the airbill attached to the box, so shipping your custom bass is scary, as every goof that touches it see's that it is worth $XXXX.00!
2) Get insurance--real instrument insurance, not homeowners or renters insurance.
3) No, you can't carry on, except sometimes you can.
4) No, you can't put it in the forward coat closet, except sometimes you can.
5) No, a regular hardshell case will not provide much protection.
6) Arrive 2 hours in advance of your flight. Expect TSA to act like you are traveling with a firearm (OK, it's their job).
7) If you show up with your bass in a gig bag, you are begging for heartbreak (and other kinds of BREAK).
8) Call the airlines all you want, it is a total waste of your time.
9) Read the Airlines baggage policies and rules all day long, and then forget them, because you have no rights at all once they have your money and your instrument.
10) Don't be an idiot and paint your road case Olive Drab, like some people I know....
Here is how I do it: