§ 251.5 Large musical instruments as checked baggage.
Primary source
Verbatim text below is from the Electronic Code of Federal Regulations (eCFR), a public-domain U.S. government work. Always verify the current version with the eCFR before relying on it for any legal matter.
Full Text
Each covered carrier shall transport as baggage a musical instrument that is the property of a passenger traveling in air transportation that may not be carried in the aircraft cabin if
(a) The sum of the length, width, and height measured in inches of the outside linear dimensions of the instrument (including the case) does not exceed 150 inches or the applicable size restrictions for the aircraft;
(b) The weight of the instrument does not exceed 165 pounds or the applicable weight restrictions for the aircraft; and
(c) The instrument can be stowed in accordance with the requirements for carriage of carry-on baggage or cargo established by the FAA.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.