An aircraft registration is a unique alphanumeric string that identifies a civil aircraft, in similar fashion to a licence plate on an automobile.

In accordance with the Convention on International Civil Aviation all aircraft must be registered with a national aviation authority and they must carry proof of this registration in the form of a legal document called a Certificate of Registration at all times when in operation.

Most countries also require the aircraft registration to be imprinted on a permanent fireproof plate mounted on the fuselage for the purposes of post-fire/post-crash aircraft accident investigation.
Because aeroplanes/airplanes (See British and American spelling differences) typically display their registration numbers on the aft fuselage just forward of the tail, in earlier times, more often on the tail itself, the registration is often referred to as the “tail number”.

Although each aircraft registration 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.[1] It had been previously assigned to a Beechcraft Bonanza (specifically, the aircraft in which Buddy Holly was killed). Also note that 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.

International standards

The first use of aircraft registrations was based on the radio callsigns allocated at the London International Radiotelegraphic Conference in 1913. This was modified by agreement by the International Bureau at Berne and published on April 23, 1913. Although initial allocations were not specifically for aircraft but for any radio user, the International Air Navigation Convention held in Paris in 1919 made allocations specifically for aircraft registrations, based on the 1913 callsign list.

The agreement stipulated that the nationality marks were to be followed by a hyphen then a group of four letters that must include a vowel (and for the convention Y was considered to be a vowel).
At the International Radiotelegraph Convention at Washington in 1927, the list of markings was revised and adopted from 1928; these allocations are the basis of the currently used registrations. The markings have been amended and added to over the years, and the allocations and standard are managed by the International Civil Aviation Organization (ICAO).
Article 20 of the Chicago Convention on International Civil Aviation (signed in 1944) requires that all signatory countries register aircraft over a certain weight with a national aviation authority. Upon registration, the aircraft receives its unique “registration”, which must be displayed prominently on the aircraft.
Annex 7 to the Convention on International Civil Aviation describes the definitions, location, and measurement of nationality and registration marks. The aircraft registration is made up of a prefix selected from the country’s callsign prefix allocated by the International Telecommunication Union (ITU) (making the registration a quick way of determining the country of origin) and the registration suffix. Depending on the country of registration, this suffix is a numeric or alphanumeric code, and consists of one to five digits or characters respectively.
The ICAO provides a supplement to Annex 7 which provides an updated list of approved Nationality and Common Marks used by various countries.

Country-specific usage

When painted on the fuselage, the prefix and suffix are usually separated by a dash (for example, YR-BMA). When entered in a flight plan, the dash is omitted (for example, YRBMA). In countries that use a number suffix rather than letters, like the United States (N), South Korea (HL), and Japan (JA), the prefix and suffix are connected without a dash.

Aircraft flying privately usually use their registration as their radio callsign, but many aircraft flying in commercial operations (especially charter, cargo, and airlines) use the ICAO airline designator or a company callsign. In some instances, it may be sufficient to simply display the suffix letters, with the country prefix omitted. For example, gliders registered in Australia would omit the VH prefix and simply display the suffix. Obviously, this is only suitable where the aircraft does not fly in the airspace of another country.

Even if the suffix usually consists of alphabetical characters in a certain country, gliders and ultralights may sometimes use digits instead. For example, in Germany, D-ABCD will be a powered airplane while D-1234 is a glider. In Australia, early glider registration suffixes began with the letters “G-AU”, and it is not uncommon to find such gliders only displaying the last two letters of the suffix, as they lacked the range to travel internationally. For example, VH-GIQ would simply be displayed as IQ.

Different countries have different registration prefixes: Canadian registrations start with C, British with G, German with D, and so forth. A comprehensive list is tabulated below.

Pre-1928 Allocations

Note: in the suffix pattern, n represents a number, x represents a letter