The final rule does not change the earlier provisions of the Act, but mercifully puts a period at the end of the sentence: "Section 403 of the Act and this final rule provide that carriers are required to allow passengers to stow their musical instruments in an approved stowage area in the cabin only if at the time the passenger boards the aircraft such stowage space is available.
"With the exception of certain disability assistance devices, overhead bins or under seat stowage space is available to all passengers and crew members for their carry-on baggage on a “first come, first served” basis. Accordingly, carriers are not required to remove other passengers’ or crew members’ carry-on baggage that is already stowed in order to make space for a musical instrument. However, this also means that carriers are not allowed to require a passenger to remove his or her musical instrument that is already safely stowed (e.g., in the overhead bin) to make room for carry-on baggage of other passengers who board the aircraft later than the passenger with the musical instrumenT." Most importantly, "This is true even if the space taken by the musical instrument could accommodate one or more other carry-on items." You can read the entire text of the rule here.
The DOT has also provided a helpful page with links to procedures for complaining to an airline or to the DOT regarding air travel with instruments, and tips for traveling with a musical instrument, available here.
Best advice? Print a copy of the rule and carery it on with you when you travel so you can stop arguing with that officious ticket agent who insists that you have to check your guitar as baggage or buy another seat for it.
Wallace Collins is an entertainment and intellectual property lawyer with more than 30 years of experience based in