Traveling with a French Horn?

Don't count on the horn as a carry on. Best case scenario is the stewardess sees it and asks if it is a musical instrument and takes care of it for you. (yes I have heard of that happening) worst case is they see it and say you have to check it, no ifs ands or buts. If you have connecting flights its even harder to take it on. If it's not yours I would NOT risk it. The trumpet ought to fit as a carry on. Check online but as long as it is within the required dimensions they can't do much. Another possibility is to just take the mouthpiece for the horn and do 20-30 min of buzzing each day to keep your embouchure in shape. You could also buy a buzz tube and put it in your checked baggage.