The Early Days of Air Traffic Control

In the pioneer days of aviation, a pilot relied on eyesight and navigated with a map, following ground landmarks such as highways and railroads. Rules to reg­ulate air navigation were first introduced in the 1920s. The first air traffic con­troller began work in 1929 in St. Louis, Missouri. English became the interna­tional language of air traffic control, and agreed-upon words were adopted to prevent misunderstandings. At this time, radio was used to communicate with planes, but there was no radar to track aircraft movement until the 1940s.

The International Civil Aviation Organization (ICAO) was set up in 1947. Today, this agency of the United Nations regulates air traffic control worldwide as well as the boundaries of national airspace. It allocates call signs to each airline flight, usually an abbreviated form of the airline name (such as GLA for Great Lakes Airlines) followed by the number of the flight—for example, GLA 674 for flight 674. The call signs appear on radar screens, on flight plans, and on information boards at airports. Other civilian aircraft are usually identi­fied by their registration numbers, a combination of letters and numbers dis­played on the tail and wings—N3761P, for example. (The “N” is the interna­tional designation for the United States.)