The Transportation Security Administration (TSA) has established specific requirements for transporting firearms and ammunition in checked baggage on commercial aircraft, including the following:

All firearms or ammunition must be checked with the air carrier as luggage or inside checked luggage. Firearms, firearms parts, and ammunition are prohibited from carry-on baggage. Firearm parts include barrels, magazines, frames, and other internal parts of a firearm.
Gun owners are strongly encouraged to double-check all baggage, even when not traveling with firearms.  This is particularly important if bags also serve as range bags or are used to transport firearms and/or ammunition at other times. Inadvertently leaving ammunition or a firearm in a carry on bag will result in serious delays at security points and potential civil or criminal penalties.

• All firearms and/or ammunition must be declared orally or in writing in accordance with the air carrier’s procedures. Civil and criminal penalties may be applied for failure to declare a firearm in checked baggage.
• All firearms must be unloaded.
• The firearm must be carried in a hard-sided container. The container must be locked and only the passenger may retain the key or combination.

All checked baggage is subject to inspection. If during the inspection process it is necessary to open the container, the air carrier is required to locate the passenger and the passenger must unlock the container for further inspection. The firearm may not be transported if the passenger cannot be located to unlock the container. If you are traveling with a firearm, pay close attention to airport pages and announcements. If requested, provide the cooperation necessary to inspect your firearm.

• Ammunition is prohibited from carry-on luggage. Ammunition must be transported in the manufacturer’s packaging or other packaging suitable for transport. Consult your air carrier to determine quantity limitations and whether the ammunition must be packed separately from the firearm. Because the level of training among airline personnel varies widely, passengers would be well advised to bring printed copies of firearms rules from both TSA and the particular airline being used. For further information, visit www.tsa.gov/traveler-information/firearms-and-ammunition

Finally, the United States Department of Justice has issued a written opinion that federal law protects airline travelers with firearms, assuming: (1) the person is traveling from somewhere he or she may lawfully possess and carry a firearm; (2) en route to the airport the firearm is unloaded and inaccessible from the passenger compartment of the person’s vehicle; (3) the person transports the firearm directly from his vehicle to the airline check-in desk without any interruption in the transportation, and (4) the firearm is carried to the check-in desk unloaded and in a locked container. DoJ Opinion Letter
Otherwise, travelers should strictly comply with FOPA and with airline and TSA policies regarding firearms transportation, avoid any unnecessary deviations on the way to checking in their baggage, be well acquainted with the firearms laws of the jurisdictions between which they are traveling, have any necessary permits or licenses ready for inspection, and have copies of relevant provisions of current law or reciprocity information printed from official sources.
Special advisory for New York & New Jersey airports: Despite federal law that protects travelers, authorities at JFK, La Guardia, Newark, and Albany airports have been known to enforce state and local firearm laws against airline travelers who are passing through their jurisdictions.In some cases, even persons traveling in full compliance with federal law have been arrested or threatened with arrest. FOPA’s protections have been substantially narrowed by court decisions in certain parts of the country, particularly in the Northeast. Persons traveling through New York and New Jersey airports may want to consider shipping their firearms to their final destinations rather than bringing them through airports in these jurisdictions.
Below are links to information from specific airlines:
Alaska Airlines
American Airlines
Delta Airlines
First Air
Frontier Airlines

Jet Blue
Southwest Airlines
United Airlines
Virgin America

For more information about the interstate transportation of firearms, please see  Guide To The Interstate Transportation Of Firearms
Also, see information about the BATFE Form For Nonimmigrant Aliens