Musical Instruments are allowed on-board most airlines, however it is important to check whether you will be able to bring your instrument as a piece of carry-on luggage, check it in as a piece of regular baggage, or whether you will need to purchase an additional seat inside the cabin to strap in your contrabass or cello.
The rules and regulations on bringing an instrument on-board with you onto the plane as a piece of carry-on vary by airlines, although most airlines will allow you to bring a small instrument such as a small guitar, violin, ukulele, flute, etc. in place of your piece of regular luggage, even if the dimensions slightly exceed the standard carry-on baggage dimensions. It is important that the instrument be able to fit easily into the overhead compartment. Depending on the airline and the flight crew of your flight, you may be able to place a guitar or instrument into a separate storage compartment such as the little closet near the business-class section of the plane, so that the instrument does not get damaged by your fellow travellers stuffing oversize carry-on bags onto the neck of your guitar.
Be sure to note whether your airline allows free carry-on bags, and how many are included. Some discount airlines (and special fare types on some airlines) have a very strict carry-on allowances, which mean that you may not be able to bring an instrument on-board, unless it is your ONLY piece of carry-on baggage. Be sure to double-check the carry-on allowances for your airline before flying (and preferrably, before booking your flight).
When bringing a guitar on-board, there have been some situations where airport security was not happy to bring extra guitar-strings, as it was considered dangerous, so you may want to consider packing extra strings into your regular checked baggage, rather than bringing them as carry-on.
When flying with a larger instrument such as a cello or contrabass, you will almost always be allowed to bring it on-board with you into the cabin, as long as you purchase a additional seat for your instrument. Depending on the airline, you may have to purchase the additional seat at the full adult fare (always book the seat right beside you), or some airline offer a discounted ticket to purchase an additional seat for your instrument. Of course, there are some airlines that will charge extra for purchasing an additional seat for an instrument, so these airlines should be avoided.
When bringing your instrument onto the plane, you will be responsible to carrying it on yourself. Some gate-agents may not be familiar with such large items being brought onto the plane, so be sure to inform that you purchased a additional seat specifically for your instrument. Try to board together with the first group when the gate agent allows board for families with small children and people requiring extra assistance. Often when they see the size of the instrument, you will be allowed to join, which will make it much easier to maneuver your instrument without other passengers crowding you from behind.
If your instrument doesn't seem to fit between seat cushion and the seat in front of you, it is often possible to remove the seat cushion from the seat. The seat cushions are often used as floatation device in case of emergency, and are simply attached by velcro. Pull off the velcroed seat-cushion, and you will have plenty of space to place your instrument without it getting crushed if the passenger in front decides to lean back their seat. In order to secure the instrument in place, you will use the seat belt, and may sometimes require to bororw a seat belt extender strap to make it all the way around. When de-planing at the end of the flight, it is courteous to wait until all of the passengers get off before working your instrument out of its seat and off the plane.
With most airlines, it is possible to check-in an instrument as a piece of regular luggage, simply paying the regular baggage fee for your instrument. Often the oversize charge is waived (but not always, this is airline-dependent), but you will usually be charged any applicable overweight fees for your instruments. Usually, all standard baggage fees will apply when checking in your instrument. Be sure to protect it by packing your instruments in hard-sided cases, and drop them off at the oversize baggage drop area. Depending on your destination airport, and size of the instruments, they may come out on the regular baggage carousel or at a dedicated oversize/oddly shaped baggage carousel, often found on the periphery of the baggage claim area.
The US Department of Transportation (D.O.T.) has written up federal rules that airlines must comply with regarding the carriage of musical instruments on aircraft. These rules protect musicians and their instruments by stipulating for what services airlines may and may not charge passengers carrying instruments. Although these rules apply only to US-based airlines, many international airlines follow the same guidelines.
The FAA states that airlines “shall permit a passenger to carry a violin, guitar, or other small musical instrument in the aircraft cabin” without an additional fee (standard carry-on charges would apply). The instrument must fit under the seat or in the baggage compartment.
251.3 Small Musical Instruments as Carry-on Baggage
Each covered carrier shall permit a passenger to carry a violin, guitar, or other small musical instrument in the aircraft cabin, without charging the passenger a fee in addition to any standard fee that carrier may require for comparable carry-on baggage, if
(a) the instrument can be stowed safely in a suitable baggage compartment in the aircraft cabin or under a passenger seat, in accordance with the requirements for carriage of carry-on baggage or cargo established by the FAA; and
(b) there is space for such stowage at the time the passenger boards the aircraft.
The new rules also allow passengers the right to purchase an additional seat on-board the aircraft to carry their instruments, without any additional charges.
251.4 Large Musical Instruments as Carry-on Baggage
Each covered carrier shall permit a passenger to carry a musical instrument that is too large to meet the requirements of section 251.3 in the aircraft cabin, without charging the passenger a fee in addition to the cost of an additional ticket described in subparagraph (e), if
(a) the instrument is contained in a case or covered so as to avoid injury to other passengers;
(b) the weight of the instrument, including the case or covering, does not exceed 165 pounds or the applicable weight restrictions for the aircraft;
(c) the instrument can be stowed in accordance with the requirements for carriage of carry-on baggage or cargo established by the FAA;
(d) neither the instrument nor the case contains any object not otherwise permitted to be carried in an aircraft cabin because of a law or regulation of the United States; and
(e) the passenger wishing to carry the instrument in the aircraft cabin has purchased an additional seat to accommodate the instrument.