The anatomy of aircraft registration
WHEN AN aircraft is built, the manufacturer will assign a unique identifier called a serial number to it. A registration, or tail number, differs from a serial number, as it is assigned when an aircraft joins an aircraft registry. Unlike the serial number, if the aircraft changes owners, the registration often changes.
That is not to say that registrations are not unique. They are, as only one instance of a civil aircraft registration is permissible at one time.
The prefix, the beginning part of the registration, denotes the country in which the aircraft is registered. Following this there can be a dash, or a series of numbers. In the case of the US, the largest register in the world, the prefix is N, which is then followed by up to five other characters. A number must follow the N, however after the number there can be letters, although the maximum number of letters allowed is two. But, the registration does not have to include any letters, therefore registrations such as N1 are valid, but equally valid is N123AB, as is N37547.
The usual rule with aircraft registrations is that if the prefix has one character, then then there will be four characters following the dash. If there are two characters in the prefix, then there will be three characters after the dash. For example, the prefix for France is F-, so an aircraft registered in France might be F-HMBY. The prefix for Malaysia is 9M-, so an aircraft might be registered as 9M-TMJ.
Confusingly perhaps, there are several countries that share the same prefix, and the letter immediately following the dash denotes in which country the aircraft is registered. These are normally small Caribbean island nations, although Bermuda also follows this principle.
Normally, countries that use this prefix system have the prefix VP-, so for these registries it is the letter following the dash that denotes the country. For Bermuda it is VP-B and for the Cayman Islands it is VP-C.
Another area that uses the same registration prefix is Greater China. Traditionally mainland China used B- and then a series of four numbers, Taiwan used B-and a series of five numbers, Hong Kong used B-H or B-K and a series of two letters, and Macao used B-M and then two letters.
However, with the numbers of aircraft registered on the Chinese mainland seemingly growing every day, the registration system changed recently. Some of the more-recent Gulfstream G650ERs to be registered have used B- and then three numbers and then a letter. Some of the recent airliner deliveries in the country have used two numbers followed by a letter and then another number, and some have used two numbers and then two letters.
With military aircraft there is no such rule, and aircraft can be registered however the air force dictates. Often this can lead to aircraft carrying the same registration. Sometimes this also includes business jets that are in military service. The registration 101 for example is worn by a French Air Force Dassault Falcon 10 as well as by a Pakistan Navy Hawker 800XP.
The US Air Force uses a different system of registration, with two numbers, a dash and then up to five numbers. This system uses the fiscal year that the order for the aircraft was placed for the first two numbers. So, LearJet 35A 84-582 was purchased by USAF in the fiscal year 1984