Air Traffic Control
Air Traffic Control—you've probably heard of it—but why does it exist and where did it come from?
The first control tower to use ground-to-air and air-to-ground radio communication was built in 1930 at Cleveland Airport.
As the popularity of air travel grew, so did the need for better air traffic control along the nation's air routes and especially around airports. Airlines first developed systems to control their own air traffic. However, a series of highly publicized accidents in the mid-1930s, including the crash of a DC-2 in which New Mexico Senator Bronson Cutting was killed, highlighted the critical need for a national system. The federal government stepped in, and in 1936 the Commerce Department accepted nationwide responsibility for air traffic control.
The Beginnings of Air Traffic Control
New navigation techniques were needed to allow aircraft to fly reliably and safely at night and in bad weather. In the 1920s, the first low-frequency radio range beacon experiments were conducted along National Air Transport's New York-Chicago route. By February 1931, the entire New York to San Francisco route was equipped with radio range stations. In December 1935, the airlines established the first Airway Traffic Control Center at Newark, New Jersey. Two more soon opened at Cleveland and Chicago. The Department of Commerce took over their operation in mid-1936, and within a year eight centers were in full operation coast-to-coast. An airway modernization program was launched in 1938, and airport control towers became a familiar sight. In November 1941, with World War II sweeping through Europe and Asia, the federal government assumed responsibility for all towers deemed vital to the war effort.
Touching Down Safely
By World War II's end, two precision landing systems were available for civil use: Ground Controlled Approach (GCA), which used radar, and Instrument Landing System (ILS), which used radio transmissions.
Ground Control Approach (GCA)
With Ground Control Approach (GCA), a ground controller followed an approaching aircraft on a radar screen and instructed the pilot down to the runway. GCA was placed into operation at Washington's National Airport and Chicago's Municipal Airport in 1947. Although GCA was popular with the military, airline pilots preferred the competing ILS system.
Landing System (ILS)
The Civil Aeronautics Authority in 1947 adopted the Instrument Landing System (ILS) as its primary landing aid, supplemented by GCA at busy airports. With ILS, a pilot relied on instruments that received altitude and direction data via radio transmissions and allowed the pilot to follow a glide path to the runway. ILS greatly reduced missed approaches and flight cancellations due to weather and enabled airports to handle more traffic.
Radar Takes Over
Radar ("radio detecting and ranging") was developed by the British in the 1930s and widely used during World War II. The first U.S. civilian control tower equipped with radar began operating at Indianapolis Airport in 1946. By 1951 the use of radar had begun to supercede pilot-reported positions by radio.
Radar Departure Control made its debut at Washington's National Airport in 1952. Until then, radar had been used only to confirm a pilot's reported position. With the new system, controllers could provide better and safer traffic flow into and out of airports.
Did You Know?
Improved air traffic control techniques, particularly GCA, were critical to the success of the Berlin Airlift in 1948-49. For almost a year, a continuous relay of military and civilian transports landed in the Soviet-blockaded East German city every three minutes around the clock and in all weather, and kept the city's 2 million people fed.
The dramatic increase in air travel during the 1950s created a need for better airports and air traffic control. By the end of the 1950s, the aviation infrastructure in the United States had grown intricate and highly advanced. Just as new aircraft technology produced a new generation of aircraft, new electronic technology produced answers to the growing problems of communications and managing air traffic.
Growing Pains
Despite steadily improving air traffic control, a series of airliner accidents over five months in 1951-52 aroused public concern. Although not related to air traffic control, the accidents led to an accelerated program of technical development and promoted new discussions on safety and traffic control. Air traffic growth in the 1950s led to severe airport congestion and delays. In 1956, two airliners collided over the Grand Canyon. Two more midair collisions occurred in 1958 and another in 1960. These events prompted legislation that enabled aviation authorities to take corrective measures. In the 1950s, the Civil Aeronautics Administration, in cooperation with the Air Force, began installing long-range radars with a radius of 322 kilometers (200 miles). A network of overlapping radars was completed by 1965, allowing continuous monitoring of aircraft in controlled airspace.
From "Jet Way" to "Jetway"
The upsurge in air travel led to the development of modern airports. Chicago's O'Hare International Airport introduced the first "air bridges." Better known by the brand name "Jet Way," they provided sheltered passage between terminal and plane and sped up aircraft turnaround times. However, passengers now sometimes never even saw the airplane they were boarding. "Jetway" is an example of a brand name that became a generic term, similar to Kleenex, Chapstick, or Jet Ski.
Air Traffic Control Today
Every moment of every day, thousands of aircraft safely cross the skies over the United States. Each is carefully watched and directed to its destination by an interconnected system of air traffic control along well chosen routes.
Severe weather causes more than 70 percent of air traffic delays and costs the airlines billions of dollars every year. Lightning alone causes 33 percent of these losses. Air traffic controllers work constantly to minimize weather disruptions, while ensuring that every flight arrives safely.
Despite the severe challenges of weather, as well as airport congestion, the Federal Aviation Administration's professional workforce ensures that commercial aviation remains the safest form of travel.
STEM in 30
Top of the Tower: How Air Traffic Control Keeps Skies Safe
Air traffic controllers are in charge of keeping the skies orderly and safe, relaying information to pilots while they are in the air. In this episode, learn about what information air traffic controllers give to pilots in order to ensure safe flying, as well as how weather impacts air traffic and what was the hardest day to be an air traffic controller.
