designators used by American Airlines: Call signs (flight identification or flight ID) Most airlines employ a call sign that is normally spoken during airband radio transmissions. As by ICAO Annex 10 chapter 5.2.1.7.2.1 a call sign shall be one of the following types: Type A: the characters corresponding to the registration marking of the aircraft. Type B: the telephony designator of the aircraft operating agency, followed by the last four characters of the registration marking of the aircraft. Type C: the telephony designator of the aircraft operating agency, followed by the flight identification. The one most widely used within commercial aviation is type C. The flight identification is very often the same as the flight number, though this is not always the case. In case of call sign confusion a different flight identification can be chosen, but the flight number will remain the same. Call sign confusion happens when two or more flights with similar flight numbers fly close to each other, e.g., KLM 645 and KLM 649 or Speedbird 446 and Speedbird 664. The flight number is published in an airline's public timetable and appears on the arrivals and departure screens in the airport terminals. In cases of emergency, the airline name and flight number, rather than the call sign, are normally mentioned by the main news media. Some call signs are less obviously associated with a particular airline than others. This might be for historic reasons (South African Airways uses the callsign "Springbok", hearkening back to the airline's old livery which featured a springbok), or possibly to avoid confusion with a call sign used by an established airline. Companies' assigned names may change as a result of mergers, acquisitions, or change in company name or status; British Airways uses BOAC's old callsign ("Speedbird"), as British Airways was formed by a merger of BOAC and British European Airways. Country names can also change over time and new call signs may be agreed in substitution for traditional ones. The country shown alongside an airline's call sign is that wherein most of its aircraft are believed to be registered, which may not always be the same as the country in which the firm is officially incorporated or registered. There are many other airlines in business whose radio call signs are more obviously derived from the trading name. The callsign should ideally resemble the operator's name or function and not be confused