When nobody was in charge
In the first years of aviation, there was little to control. Early airfields were open fields where a few aircraft landed into the wind, and pilots simply looked out for one another. Collisions were a hazard, but there were few enough flights that the problem was manageable. As flying became more common after the First World War, particularly with mail and passenger services, the risk grew, especially near busy airports and in bad weather.
The first approaches were simple. Ground staff used colored flags, lamps, paddles and ground markings to tell pilots whether it was safe to land. Windsocks showed wind direction. Airfield operators watched the sky and signaled to approaching aircraft. These methods depended entirely on line of sight, which failed in fog and cloud.
Early radio and the first towers
Radios small enough to be carried in aircraft were being tested around the end of the First World War. In the early 1920s, airports such as London Croydon in England are often described as pioneers of radio communication between ground staff and pilots, using wireless messages, initially in Morse code and later by voice. Croydon is commonly cited for its early control office and tower, though other airfields in Europe and the United States also developed their own practices around the same time. Because several places did similar things, “first control tower” is a title that different sources assign to different airports.
In the United States, Archie League is often credited as one of the first air traffic controllers. In 1929 he worked at the airfield in St. Louis, directing aircraft by waving colored flags from a platform. Over the following years, airports built purpose-designed towers with a glassed-in room (the cab) high above the field, which gave controllers a view in all directions. Voice radio gradually replaced flags for ordinary traffic, though light signals remained as a backup in case of radio failure and are still used today.
Controlling flights between airports
A tower directs traffic near an airport, but aircraft spend most of their time flying between cities. In the mid-1930s, the airlines in the United States set up centers to track flights along their routes. The first of these is usually said to have opened in Newark, New Jersey, in 1935, and the system was soon taken over by the federal government. Controllers at these centers followed aircraft by radio position reports, updated on charts or boards, and set minimum separations in time and altitude. This was slow and relied on pilots’ estimates of where they were, a method sometimes called procedural control.
Pilots in cloud used instruments only, which meant that the controller could not see them either. The system therefore relied on strict rules for altitudes, routes and reporting points, which are the basis of instrument flight rules.
Radar changes the picture
Radar, developed in the late 1930s and during the Second World War for military radar detection, offered a way to see aircraft directly. After the war, radar technology was adapted for civilian airports and en route control, and radar scopes began to show controllers a live picture of traffic. The same underlying technology is the subject of the broader story of civilian radar. Over the 1950s, controllers gained the ability to guide aircraft through approach paths in poor visibility, including by talking pilots down on precision approach radar at some airfields.
A major turning point in the United States came after a collision over the Grand Canyon in 1956 between two airliners, which killed everyone on board. The accident is widely credited with increasing political pressure to modernize air traffic control, and the Federal Aviation Agency, later renamed the Federal Aviation Administration, was created in 1958. Other countries developed their own agencies and arrangements, and international bodies agreed shared standards over time.
Computers, transponders and layers
From the 1960s onward, secondary radar and transponders became important. Instead of just reflecting a radar pulse, a transponder in the aircraft replies with a code and, in many systems, altitude. This made aircraft easier to identify on screen. Computers processed flight plans and radar data, displaying data tags next to each aircraft symbol. Later systems added collision-warning alerts for controllers and, on aircraft, onboard collision avoidance equipment.
Today’s air traffic control has several layers. Tower controllers handle takeoffs, landings and movements near the runways. Approach and departure controllers manage aircraft in the airport area. En route centers handle the long middle part of a flight, covering large regions of airspace. Satellite-based systems are increasingly used to report aircraft position, an area where global positioning data now supplements radar.
What a tower does and does not do
It is easy to think of a tower as simply “steering” planes. In practice, controllers keep aircraft apart and in an orderly sequence, while pilots remain responsible for flying their aircraft. Much of the system’s strength lies in rules, trained people and redundancy, not any single piece of equipment. The story of the control tower is a story of aviation growing so busy that safety depended not only on better aircraft but on organized cooperation on the ground.