Bruce, I have flown a number of times both domestically as well as internationally with various airlines and most airlines (BUT NOT ALL) as I discovered, will allow you to take your violin on board as one piece of your carry-on baggage. Note that some airlines will only allow ONE item as carry-on.
I (and many others) would suggest that you try to get onto the aircraft as quick as possible in order to find a vacant overhead locker near to your seat. I have found that it worked best for me to put the violin in the overhead locker opposite my seat so I could keep a constant eye on it when other passengers were either cramming their bag in or taking it out. A few passengers may think you crazy to be so concerned about a violin (as I experienced) but they are just the ignorant ones (whom we must bless) who know nothing about the fragility of a violin.
Also, if you smile a lot when boarding, you will often find a very helpful flight attendant who will help you quickly find a vacant locker. BY NO MEANS EVER LET YOUR FIDDLE GO INTO THE CARGO HOLD.
Sorry for the late response. Hope this helps.