An aircraft registration is a code unique to a single aircraft, required by international convention to be marked on the exterior of every civil aircraft. The registration indicates the aircraft's country of registration, and functions much like an automobile license plate or a ship registration. This code must also appear in its Certificate of Registration, issued by the relevant civil aviation authority (CAA). An aircraft can only have one registration, in one jurisdiction, though it is changeable over the life of the aircraft. Legal provisions In accordance with the Convention on International Civil Aviation (also known as the Chicago Convention), all civil aircraft must be registered with a civil aviation authority (CAA) using procedures set by each country. Every country, even those not party to the Chicago Convention, has an NAA whose functions include the registration of civil aircraft. An aircraft can only be registered once, in one jurisdiction, at a time. The NAA allocates a unique alphanumeric string to identify the aircraft, which also indicates the nationality (i.e., country of registration) of the aircraft, and provides a legal document called a Certificate of Registration, one of the documents which must be carried when the aircraft is in operation. The registration identifier must be displayed prominently on the aircraft. Most countries also require the registration identifier to be imprinted on a permanent fireproof plate mounted on the fuselage in case of a post-fire/post-crash aircraft accident investigation. Most nations' military aircraft typically use tail codes and serial numbers. Military aircraft most often are not assigned civil registration codes. However, government-owned non-military civil aircraft (for example, aircraft of the United States Department of Homeland Security) are assigned civil registrations. Although each aircraft registration identifier is unique, some countries allow it to be re-used when the aircraft has been sold, destroyed or retired. For example, N3794N is assigned to a Mooney M20F. It had been previously assigned to a Beechcraft Bonanza (specifically, the aircraft in which Buddy Holly was killed). An individual aircraft may be assigned different registrations during its existence. This can be because the aircraft changes ownership, jurisdiction of registration, or in some cases for vanity reasons. Choice of aircraft registry Most often, aircraft are registered in the jurisdiction in which the carrier is resident or based, and may enjoy preferential rights or privileges as a flag carrier for international operations. Carriers in emerging markets may be required to register aircraft