Thanks for the info.... I looked at the United page for musical instruments, and it connected to this link:

https://www.united.com/web/en-US/con...gage/seat.aspx

Which states:

United Airlines will allow a customer to purchase a ticket for an item, approved by a United agent, which is too fragile or bulky to be handled as checked baggage. These items can be carried on board and transported in a seat.

Examples of cabin-seat baggage may include large or valuable musical instruments, media cameras, artifacts, garment bags and similar items of a delicate nature or unusual size. Note that guitars are not considered cabin-seat baggage and customers traveling with guitars should continue to follow carry-on baggage guidelines.

The following restrictions apply:

Must not exceed 165 pounds (75 kg).
Must be packaged or covered in a manner to avoid injury to other customers.
Must be secured in a seat adjacent to the owner.
Must be properly secured by a seat belt to avoid shifting during flight.
Must not restrict access to, or use of, any regular or emergency exit or aisle of the cabin.
Must not obscure any customer's view of "seatbelt," "no smoking" or "exit" signage.
Must not contain dangerous goods.
Must be reserved in advance and applicable charges paid.
Please check with a United agent for pricing information.

I emphasized a couple of item in italics, and in this case, it may not have been possible.