Aircraft registration marks identify the country in which an aircraft is registered, but their remaining characters can also indicate weight category, manufacturer, fleet position or operator preferences. National aviation authorities apply different systems, while airlines and owners often use the available characters to organise fleets or create recognisable patterns.
The prefixes originated in radio call-sign allocations by the International Telecommunication Union more than a century ago. Early assignments followed the 1919 Paris Aviation Convention and were reorganised after the 1927 Washington Radiotelephony Convention. Germany uses one of the most detailed systems: the first character after D- can indicate an aircraft’s weight class and, in some cases, its engine configuration. Separate conventions apply to helicopters, gliders, ultralight aircraft, motor gliders, airships and balloons.
Airlines add their own logic where national rules allow it. Lufthansa uses letters to identify manufacturers, including B for Boeing, I for Airbus, E for Embraer and D for Douglas or McDonnell Douglas, although exceptions exist. Swiss uses sequential marks for its Airbus A220 fleet, including HB-JBA through HB-JBH and HB-JCA through HB-JCJ.
Other systems provide different clues. Spanish registrations follow the domestic registration sequence, while France uses O after F for overseas territories. US registrations begin with N and can contain up to five further numbers or letters. The characters after a national prefix may therefore be systematic, operator-selected or arbitrary, depending on the country and owner.