A number of people on this forum have mentioned bringing a tuba on board a plane as an extra seat item, but I haven't found anyone mentioning that they brought a sousaphone onto a plane, paying for an extra seat. That's what I'm hoping to do on a two-leg, transatlantic trip.
Some background: I was given an old 1950s 20k, a bit of a fixer-upper and want to bring it with me to Italy ( where I live). The people at Delta did not give me precise dimensions, so I'm hopeful it could fit in a seat. But I thought I'd ask the Tubenet community if anyone has positive or negative experiences.