At any given moment, there are more than 10,000 aircraft in the air. They fly along the same routes and use the same airports, taking off and landing within moments of each other. And yet, statistics show that flying is by far the safest way to travel.
This is thanks to air traffic control.
While powered flight is undoubtedly one of humankind’s greatest achievements, the companion technologies that keep it safe are no less impressive. In this article we’ll go over some key points in the history of air traffic control, some of the technologies that it comprises, and we’ll look at where it’s headed in the future.
The birth of air traffic control
In the first years of powered flight there was no need for air traffic control because there wasn’t any air traffic. But it didn’t take long. The first airplane flew in 1903, and by 1914 a pair of entrepreneurs had set up the first airline - a 25-minute route between St. Petersburg and Tampa in Florida.
Benoist Type XIV of the St.Petersburg Tampa Airboat Line, 1914. Credit: Björn Larrson
But this wasn’t exactly traffic – the airline only had two planes and went out of business in a few months. The need for air traffic control was born in the First World War. The demands of aerial combat gave us faster, bigger, and more reliable planes, as well as many people who were trained to fly them. The first airline to fly daily international flights was born during the war as a military relief mission between England and Belgium. From 1918, “Aircraft Transport and Travel” would take two passengers at a time between London and Paris, and by the early 1920s there were at least 30 commercial airlines around the world.
In short, it didn’t take long for the sky to start filling up. And now that there was traffic, that traffic needed to be managed.
1919
When the war ended, the League of Nations created the International Commission for Air Navigation (ICAN) as part of the Treaty of Versailles. It laid out the first principles of air regulation, and they are still relevant today:
1. Each nation has sovereignty over its airspace, including the right to deny entry and regulate flights.
2. A nation’s airspace rules to any aircraft in that airspace, whether domestic or foreign.
3. Aircraft should be treated equally in the eyes of each nation's law.
4. Aircraft must be registered to a state, and they possess the nationality of the state in which they are registered.
1920
The first air traffic control tower was erected at London Croydon in 1920. The Aerodrome Control Tower was a wooden hut on stilts that oversaw the aerodrome. From within, Civil Aviation Traffic Officers would provide navigation, weather and traffic information to pilots over the radio - if the airplane had one. From 1922, the airport also used radio technology to aid navigation. Called ‘Wireless Position Finding’, it enabled pilots to trace the source of a radio transmission by way of a goniometer, giving them a route to follow. It could also be used to (approximately) triangulate an airplane’s position, providing the signal from the airplane was picked up by two ground stations. Those positions were then marked with pins on paper maps.
De Havilland DH.16 of Aircraft Transport & Travel, probably Croydon, 1920. Credit: Wikipedia Creative Commons
1921
The first beacon towers were built in the USA. Here, airmail was the first major use of aircraft, and the first intercity airmail route was established in 1918. Airmail piloting was an extremely dangerous profession due to the fact that De Havilland DH-4s had no navigation equipment or radios - 35 of 200 pilots were killed between 1918 and 1926! Pilots would rely on visual cues to find their way, which sometimes included bonfires lit for that purpose. In 1921, authorities began building towers with rotating beacons to light the way, and by 1923, there was a lighted route across the country.
De Havilland airmail plane, 1922. Credit: Wikipedia Creative Commons
1922
Two accidents motivated two ATC innovations. First, a minor collision between two aircraft at Croydon airport led to a NOTAM that pilots must receive a sequence number and approval before taking off, that approval being given by a red flag waved from the tower. The second collision was not so minor – two passenger aircraft traveling between England and France collided north of Paris due to poor weather conditions that limited visibility, killing seven people. As a result, the British Air Ministry established some regulations that you may recognize:
1. Defined air routes were to be created between key destinations in Europe.
2. Pilots were to fly within these routes, and always keep to the right.
3. All aircraft were mandated to have radio aboard.
4. New aircraft must be manufactured with pilot visibility in mind.
1926
The Air Commerce Act was passed in the USA. Before this, aircraft were not regulated at all. Stunt flying (called barnstorming) was a popular spectator event, but the constant crashes didn’t instill confidence in the airplane as a mode of travel. Thus, the aviation industry petitioned the government to crate regulations. The Air Commerce Act put the government in charge of aviation, and laid down rules that, again, are still valid today:
1. Aircraft must be inspected for airworthiness.
2. Aircraft must have visible identification markings.
3. Pilots must be licensed and pass aeronautics and physical tests.
Pilot “Jersey" Ringel performing a wing walk, July 1921. Source: Wikimedia Commons
1929
The USA’s first control tower was built at Cleveland Airport. It was fitted with two-way radio in 1930. By this time, 3.5 tons of mail was being flown annually - a sevenfold increase from 1926 - and there were 61 passenger lines in operation throughout the country.
1932
The US upgraded its beacon towers to radio beacons, building a network of 83 across the country. Radio beacons enabled pilots to follow radio transmissions to an airport, which was much safer and more reliable than visual cues. It could also be used to triangulate plane positions.
1936
The first three Air Route Traffic Control Centers (ARTCC) were opened in Chicago, Cleveland and Newark. Their job was to track flights as best they could on paper maps. It was challenging because they had no direct contact with aircraft, instead communicating with control towers and radio operators who would relay information to pilots.
Air traffic controller Bill Darby, Newark, 1936. Credit: FAA
Radar
Radio waves were first demonstrated by Heinrich Hertz in 1886, and almost immediately, their characteristic of bouncing off metallic objects was investigated for practical use. It was with this principle that German physicist Christian Hülsmeyer built the ‘Telemobiloscope’, the grandfather of modern radar, in 1903. It was designed for use in ships: a rotating antenna would transmit broad radio signals, and if one bounced back, a bell would ring. Use for aircraft was investigated in several countries throughout the 1930s, but it was the British who first put it to use with the ‘Chain Home’ - a system of radar stations that is credited with allowing the outnumbered RAF to win the Battle of Britain.
Chain Home installation, Sussex, 1945. Credit: Imperial War Museum
1946
With the war over and air traffic growing rapidly, the US Civil Aeronautics Administration erected its first radar tower for civil flights.
1956
Two passenger aircraft collided over the Grand Canyon. At that time, pilots couldn’t communicate directly with air traffic controllers, but with radio operators who would relay information between the parties. The two aircraft had routes that intersected over the Grand Canyon, and due to a miscommunication, they both crossed at the same time and at the same altitude. There were no survivors.
This tragic event motivated the US government to increase investment in its air traffic control system and to establish the Federal Aviation Agency in 1958. This new agency unified airspace control across the country. Europe imitated this in 1960 with Eurocontrol.
The Civil Aeronautics Administration becomes the Federal Aviation Agency, 1958. Credit: Federal Aviation Administration
1958
The first passenger jet - the Boeing 707 - was launched. It had larger passenger capacities and slashed travel times. The jet age had begun – by 1977, there was a 1,000 percent increase in air travel in the USA alone.
1960
The FAA made the use of radar transponders mandatory in aircraft. These would send ‘squawks’ that identified individual aircraft.
1967
IBM installed the first prototype air traffic control computer at the Jacksonville ARTCC. It automatically distributed flight plan data to other ARTCCs and was operational nationwide by 1973.
IBM 9020 prototype, Jacksonville ARTCC, 1967. Source: Federal Aviation Administration
1970
The FAA established the Central Flow Control Facility. This provided a nationwide overview of air traffic, enabling high-level adjustments in cases of congestion. Today it is called the Air Traffic Control System Command Center, or ATCSCC.
1975
US airports upgraded to Automated Radar Terminal Systems (ARTS III). It automated the job of aircraft tracking by combining and correlating data inputs - both radar and human - and presenting them on a screen. This system has since been replaced by the Standard Terminal Automation Replacement System (STARS).
1995
Automatic Dependent Surveillance Broadcast (ADS-B) provided an additional layer of visibility by inverting the traditional system - instead of ground radar searching for and interrogating planes, ADS-B-equipped aircraft volunteer the information by sending reports according to the planes’ own navigation systems. Today, ADS-B is required (with some exemptions) in many jurisdictions worldwide, including Australia, across Europe and most of the US.
Air traffic control tower, Pope Field, North Carolina, 2013. Credit: Peter R. Miller
Today
Today, air traffic control comprises centralized, computerized systems that automatically register, coordinate and approve flight plans, and multiple, overlapping radar systems and visual failsafes that work in cooperation with each other to ensure every planes’ movements are tracked and accounted for. Civil and military services work together to divide a country’s airspace into sectors, with responsibility for an aircraft being transferred from sector to sector as the aircraft travels. Naturally, control is strictest in busy airspaces and especially in and around airports, where there will be several layers of radar cover, from ground radar that controls taxiing planes to long-range radar extending up to 50 nautical miles around the airport. In addition, communication between controllers and pilots has been standardized internationally – for example, the world ‘takeoff’ can’t be used at all unless approval is being actively given.
Interestingly, some things remain from the early days of flight – VFR flight rules are still relevant, for example in Class G (uncontrolled) airspace where pilots are not bound by air traffic control rules. And in many places, flight progress strips are still not digitalized, but physically handed from one controller to another as responsibility for a given plane is passed along.
Eurocontrol civil-military air traffic management coordinator with paper flight progress strips, 2006. Credit: HHaeckel
The future
While technology can always be improved upon, ATC systems have consistently maintained the best safety record of any other mode of transport, by far. But it faces a new challenge: uncrewed aerial vehicles. The lower airspace is beginning to fill up with this new form of aircraft, and traditional ATC systems are not built to cope with them. ATC technology has to evolve.
Luckily, this is not a big a leap as it sounds. Uncrewed traffic management (UTM) solutions that provide full airspace coverage are already available, which means that ATC providers simply need to integrate them alongside their existing systems. Advanced UTM systems, coupled with technologies like Remote-ID that enable drones to identify themselves from the air, will extend the capabilities of air traffic control to monitor all kinds of aerial vehicle, whether they have pilots aboard or not.
For more than 100 years, aircraft been giving people the power of flight, and air traffic control has kept them safe while doing so. Drone technology is removing those last barriers to the sky and letting more people fly than ever before. And with ATC and UTM technology working together, there’s no reason why the sky shouldn’t continue to be the safest place to be.