A decent hardshell case is the best move (and make sure the strings are slackened off).

As for stashing the violin in an overhead locker, consider what would happen if you hit bad turbulence or the plane had some problems? You can strap in but the violin can't, and 4-5lbs of violin smashing someone in the head is not exactly going to make their day, besides incidentally busting the violin. The attendants in that case were protecting your friend's instrument from your friend! ;-)

If you need your instrument to be insured, take responsibility for it yourself. A carrier will only pay up the full price if they have to, so better is to make sure you have adequate insurance for your instrument and then let the insurance company fight it out with the carrier if there's any damage. If your instrument isn't insured now, then get it insured!

Graham.