This is a bit generic, and roughly applies everywhere, randomly, consistently…. and everything in between.

Write to them/email them, get a response in writing, by email, on headed stationary. Something that you can print out, and refer the check in staff to.
If they only respond by pointing you towards their baggage policy, then you pretty much have to do one of these-

-Take a chance. On a lightly loaded flight, they might not care, on a packed flight or code share you might get told to check the guitar in as extra baggage/outsize baggage.
-forget the carry on, and check it in.
-book your ticket through an agent, and maybe pay a seat fee!


Some are sticklers. Some airlines are fairly pragmatic, but might have one or two ‘by the book’ check in staff who cannot think, only follow the rules verbatim. A lot of airlines use third party check-in staff at some stations, which can be particularly difficult.

Out of interest- is the guitar too long and heavy, or the guitar and case that it’s in?

Low cost/short haul/cheapo operators tend to allow less latitude than Lang haul/mature airlines in my experience. For some, also, the days are long gone where the Purser or the captain might make the call. In the old days, we might have a guitar fly in the flightdeck with us if the cabin were full.

Couldn’t help it! Sorry.