US law says your instrument can fly in the cabin.

What the law actually says

US air carriers must let a passenger carry a small musical instrument (violin, guitar, or other) into the cabin as carry-on if it fits safely in an overhead bin or under the seat and space is available at boarding. A larger instrument may be carried in the cabin if the passenger buys it a seat and the instrument plus case weighs no more than 165 pounds. An instrument may be checked if its outside linear dimensions (length + width + height, including the case) are 150 inches or less, within the carrier's weight rules. The statute states the limit as '165 pounds' and does not itself state a kilogram figure.

Source: 49 U.S.C. §41724 and 14 CFR Part 251 — accessed 2026-07-09. There is no equivalent EU-wide statute; EU carriers publish their own policies.