This is a list of airline codes. The table lists IATA's two-character airline designators, ICAO's three-character airline designators and the airline call signs (telephony designator). Historical assignments are also included. IATA airline designator IATA airline designators, sometimes called IATA reservation codes, are two-character codes assigned by the International Air Transport Association (IATA) to the world's airlines. The standard is described in IATA's Standard Schedules Information Manual and the codes themselves are described in IATA's Airline Coding Directory. (Both are published semiannually.) The IATA codes were originally based on the ICAO designators which were issued in 1947 as two-letter airline identification codes (see the section below). IATA expanded the two-character-system with codes consisting of a letter and a digit (or vice versa) e.g. EasyJet's U2 after ICAO had introduced its current three-letter-system in 1982. Until then only combinations of letters were used. Airline designator codes follow the format xx(a), i.e., two alphanumeric characters (letters or digits) followed by an optional letter. Although the IATA standard provides for three-character airline designators, IATA has not used the optional third character in any assigned code. This is because some legacy computer systems, especially the "central reservations systems", have failed to comply with the standard, notwithstanding the fact that it has been in place for twenty years. The codes issued to date comply with IATA Resolution 762, which provides for only two characters. These codes thus comply with the current airline designator standard, but use only a limited subset of its possible range. There are three types of designator: unique, numeric/alpha and controlled duplicate (explained below): IATA airline designators are used to identify an airline for commercial purposes in reservations, timetables, tickets, tariffs, air waybills and in telecommunications. A flight designator is the concatenation of the airline designator, xx(a), and the numeric flight number, n(n)(n)(n), plus an optional one-letter "operational suffix" (a). Therefore, the full format of a flight designator is xx(a)n(n)(n)(n)(a). After an airline is delisted, IATA can make the code available for reuse after six months and can issue "controlled duplicates". Controlled duplicates are issued to regional airlines whose destinations are not likely to overlap, so that the same code is shared by two airlines. The controlled duplicate is denoted here, and in IATA literature, with an asterisk (*). An example of this is the code "7Y", which refers to both Mid Airlines, a charter airline in Sudan, and Med Airways, a charter