100 years of air traffic control

 - August 17, 2022, 4:15 PM
During the 1920s, airplanes like this Airco DH.4 bomber, designed by Geoffrey de Havilland, were pressed into airline service, in this case for flights between London Croydon Airport to Paris. At that time, air traffic control consisted of red and green lights for takeoff.

Advances in aviation safety often happen only as a result of significant accidents. Air traffic control offers a case in point.

International rules had been drawn up in 1919 by the Commission Internationale de Navigation Aérienne (CINA) although the year when they were actually ratified by 10 countries—1922—coincided with the first midair collision between commercial aircraft. That accident, over Normandy in France, prompted countries such as the United Kingdom, France, Belgium, and the Netherlands to put the framework into action.

Philippe Domogala, an air traffic controller who is heading the 100th-anniversary celebrations for the International Federation of Air Traffic Controllers’ Associations (IFATCA), says that the situation remains largely the same and that almost all improvements to ATC have resulted from collisions and other accidents.

Domogala—who together with IFATCA colleague Philip Marien plans to publish a comprehensive history of air traffic control later this year—believes that the air traffic control field tends to react to events rather than be proactive.

Interestingly, while the first midair collision in 1922 undoubtedly accelerated the move to systematically regulate air operations, air traffic control’s year of birth is a hotly contested issue. Countries such as the UK, which were swiftly developing their own domestic aviation economies, argue that it actually occurred several years earlier.

Certainly, before the advent of the commercial aviation industry, there was no serious effort to help pilots navigate their aircraft with anything but the most basic methods of communication with ground crew.

During World War I, German airships were the first to apply goniometry—measuring the angle to the target radio source by performing direction-finding—as well as to employ a system of complex visual signals on land. Generally, however, onboard radio equipment was deemed too cumbersome for the small and arguably fragile aircraft of the day.

Most pilots of early aircraft would instead look for bonfires, lighthouses, and painted concrete arrow signals en route and, when approaching their destination airport, would watch for flares and other bespoke methods of visual signaling.

World War I Brought ATC Changes

All that changed with the end of World War I when thousands of air force pilots were able to fly the surplus military aircraft that had been quickly converted to civilian use. And so the first small commercial airlines were launched, operating from emerging aviation hubs throughout Europe in cities such as London, Paris, Brussels, Amsterdam, and Berlin.

With the birth of passenger air travel, it was becoming critical to know where aircraft were, where they were headed, and approximately when they would arrive at their destinations—information that is at the heart of air traffic control.

Since that watershed year of 1922, aircraft have been monitored using a wide array of tracking systems—employing everything from paper, wooden markers on a map, and light dots on a glass plate to radio direction finding, radar displays, and recent space-based technologies that feature satellite ADS-B surveillance.

CINA’s first international rules of the air soon made radio communication mandatory on all passenger-carrying aircraft. These aircraft—mostly biplanes carrying 12 passengers—still needed visual signaling for takeoff as radios would not work on the ground. It was not until the aircraft was airborne and when the pilot could unfurl the radio’s antenna that periodic updates on positioning could be made via either voice or Morse code.

“The departure aerodrome would meanwhile communicate with the destination, confirming takeoff time, passenger numbers, cargo, and the aircraft registration, explains CANSO, the Civil Air Navigation Services Organisation. “Weather quickly became a staple of these conversations, too. While pilots could not communicate with each other, communication with the ground was on an open frequency and there were rules of the road, such as keeping to the left of a particular landscape feature or notable landmark.”

Rules governing vertical separation between aircraft were also established at this time (300 meters when possible, 150 meters in some cases)—rules that were overseen by the first European regulatory bodies for aviation. The U.S followed suit in 1926 when it passed the Air Commerce Act, which saw the establishment of aviation regulation at the federal level as well as pilot licensing a year later. It would, however, take another two years for the first U.S. air traffic controller, Archie League, to be employed privately by St. Louis Airport to direct landings and takeoffs using flags.

The NATS tower radio room in 1928.
The NATS tower radio room in 1928.

A Revolutionary Package

The first instrument navigation package was to be used by U.S. Army Lieutenant James Doolittle in September 1929. Research at the Full Flight Laboratory, established by Harry Guggenheim, helped develop an extremely accurate barometer, a radio direction beacon to help land, and a Sperry artificial horizon and gyroscope. This equipment allowed Doolittle to fly 15 miles without having to look outside his cockpit once, which according to the founders of the Century-of-Flight.net website was revolutionary.

In the 1930s, air traffic control was developing fast. By 1933, the airspace around important aerodromes was mostly fully controlled, with pilots needing permission to enter by booking a slot before they folded up their antennas and made final preparations to land. This led to the separation of the tower control from the en route control function with specific officers in charge of managing aircraft that had yet to enter the terminal airspace.

The 1930s also saw the first use of radio beacons, which began to be sited along major routes such as the east and west coasts of the U.S., and across Europe and North Africa, reflecting the increasing range of passenger aircraft that was driving the proliferation of intercontinental routes. It was, however, the advent of the Douglas DC-3 that revolutionized air travel. Fast and with a good range, it was more reliable and carried passengers from New York to Los Angeles in 18 hours with only three stops. That maturing of aircraft technology required the simultaneous development of air traffic control, and so the centralization of ATC facilities in the U.S. was a logical next step.

Meanwhile, in Europe, the start of World War II saw a significant leap in modern radar technology. In Britain, the Royal Air Force (RAF) continued to build the Chain Home network of 40 coastal early-warning radar stations to detect and track aircraft. In Germany, the Lorenz beam blind-landing radio navigation system had been deployed at many airfields by the Luftwaffe, which also equipped most of its bombers with the radio equipment needed to use it. This was the forerunner of the modern instrument landing system, which provides horizontal and vertical positioning and distance information.

The end of World War II saw the establishment of the United Nations specialist agency the International Civil Aviation Organisation (ICAO), whose signatory states signed up to the foundational Chicago Convention. This featured specific annexes laying down the global rules for air traffic control, including phraseology and control methods such as night and bad weather landings. This framework would prove essential as—similar to what happened at the end of World War I—the large fleet of now-redundant military aircraft laid the foundation for a much bolder airline renaissance.

In 1951, 15 years after the groundbreaking DC-3 entered the stage, the Lockheed Constellation debuted. A year later, the first jet transport aircraft, the De Havilland Comet—which operated at much higher altitudes and was much faster—joined the global fleet. The superior range of both aircraft allowed airlines to be more adventurous in terms of route network and made trans-oceanic operations a reality, which in turn resulted in the development of the first oceanic control centers.

Establishing Radar-controlled Airspace

It was in 1956—more than three decades after the formative midair collision in France—that U.S. authorities moved to establish radar-controlled airspace en route after a United Airlines DC-7 struck a Trans World Airlines L-1049 Super Constellation over Grand Canyon National Park in Arizona, killing all 128 people on board. The collision took place in uncontrolled airspace, where it was the pilots’ responsibility to maintain separation using the “see and be seen” principle. The tragedy highlighted the antiquated state of air traffic control on both sides of the Atlantic, and the U.S. and Western European countries saw the need to make major aviation reforms. The development of faster aircraft in the late 1950s also underlined the need for additional separation margins—600 meters or 2,000 feet above FL290—in an effort to split these faster jets from slower air traffic.

By the 1960s, most congested air regions had become radar-controlled, and with more secondary aviation economies ramping up operations, regions soon identified the need for a far more harmonized approach to managing the airspace and procedures. This led to the formation of the pan-national air navigation agencies such as Eurocontrol in Europe and ASECNA covering much of Africa.

In 1969, the development of the Boeing 747 led to special wake turbulence separations and the arrival of the supersonic era, with the Concorde and the Tupolev 144, forced authorities to develop specific procedures and assign designated tracks and routes for these aircraft.

The 1970s saw the continued growth of air traffic, which led to the recruitment of a huge controller workforce, although poor conditions and pay led to major strikes.

The largest strike occurred in France in 1973, Domogala recalled, when the government of the day locked out the striking civilian workforce and replaced it with military controllers. Soon after, in March 1973, an Iberia McDonnell Douglas DC-9 and a Spantax Convair 990 traveling to London Heathrow airport collided over Nantes, France. All 68 people on the DC-9 were killed.

During the latter part of the decade, a major collision was occurring every year—for example, in 1976 in what is now Croatia (176 victims), in 1977 in Tenerife in the Canary Islands (583 victims), and in 1978 in San Diego (144 victims). These disasters, in which air traffic control played a part, combined with numerous hijacking incidents to put air traffic control in the spotlight.

The last major strike led by the PATCO air traffic controller union in the U.S. in 1981 resulted in the firing of 11,350 controllers and their replacement by military personnel. This sent a shockwave through the industry, leading to many ATC organizations reviewing working conditions and pay and launching equipment upgrades in a bid to head off similar industrial action in their own countries.

The first air traffic control tower, at Croydon.
The first air traffic control tower, at Croydon.

A Shock to the System

Fortunately, this system shock coincided with increased digitalization, which the industry employed to automate the many routine ATC tasks, which while improving safety also reduced controller workload. The 1990s were characterized by even more technological advances, such as electronic flight plan processing and automated data exchange between facilities, which started to make obsolete the traditional telephone technology that was used to communicate on the ground internally and between ATC facilities. Onboard TCAS and short-term conflict alert systems were also introduced as were the first examples of simulators for training.

By the 2000s, these technological advances were being steadily consolidated. Global positioning systems (GPS) were starting to replace ground-based navigation infrastructure, enabling free route airspace operations. Controller pilot data-link communications (CPDLC) were fielded while extended-range twin-engine operational performance standards (ETOPS) opened up a new range of routes and reduced vertical separation minimums (RVSM) at 1,000 feet above FL290 saw a doubling of capacity in highly congested airspace.

Tragedy struck again, however, in 2002 when a Russian-operated Tu154 collided at night over Uberlingen, Switzerland, with a cargo Boeing 757-200, killing 71 passengers, most of them children. The collision occurred after an ATC control lapse led to a conflict that generated a series of resolution advisories which the Boeing aircraft followed but the other airplane—which received a conflicting ATC instruction—did not.

Only one air traffic controller at the Zurich-area control center was controlling the airspace through which the aircraft were flying. The other controller on duty was resting, which was against regulations. Maintenance work was being carried out on the main radar image-processing system, which meant that the controllers were forced to use a fallback system while a ground-based optical collision warning system—which would have alerted the controller to the pending accident about two and a half minutes before it happened—had also been switched off for maintenance.

The subsequent murder of the air traffic controller on duty at the time of the air crash by the father of one of the victims sent another shock wave through the profession. The tragedy led to major upgrades to both TCAS and improved ATC procedures.

The next decade witnessed several technology breakthroughs with the digitalization of air traffic control, remote tower technology, and even the launch of remote control centers supported by increasing levels of automation. The focus of the industry started to move from safe separation of aircraft and preventing collisions—which was now a given—to optimizing the flow of traffic to reduce airline delays.

Here, Domogala cautioned that the famous “keeping the human in the loop” paradigm often used by engineers when developing systems has always been the professional ethos. “Humans have always been there and are in fact the real definition of air traffic control,” he said. “Most large multinational projects to achieve more automation have failed and it still is us, the human controllers, with better tools than before, of course, providing separation and control of traffic in an efficient and safe manner.”

Recovering from the Pandemic

Now, as the industry recovers from the global pandemic, which saw a drastic drop in air traffic, the priority is on trimming the costs of air traffic control for the airlines in addition to reducing aviation’s carbon footprint.

Duncan Auld, who is president of the International Federation of Air Traffic Controllers’ Associations (IFATCA), argues that as the recovery commences, fundamental questions about the way air traffic control is funded need to be asked. “We hear from all sides that aviation is at a crossroads. While we do have an opportunity to look at airspace design, optimizations, or conduct, the refresher training that has been postponed over the past years due to staff shortages, etcetera...we have been at this very same crossroads before. Every time, the way the system is set up forces it to take the easy road, the most obvious path of stopping training, not replacing staff, and hoping that, against better judgment, technology will come and save the day when it is needed.

“We need to take this opportunity to look at airspace design, defragmentation, and procedures to make substantial improvements. Such projects can use the expertise of staff that is freed up until traffic returns. This is an investment into the future of the industry, but we need a system that is willing to make this commitment and to ensure consistent funding for air navigation service providers under all circumstances.

“Humans remain essential to interpreting data and determining what is needed to separate aircraft from one another to ensure the safety of air transport,” Domogala concluded. “All the advantages and working conditions we currently enjoy have been fiercely fought for. The fatigue issues leading to reduction of hours in working continuously at the position, the early retirements, the remunerations, the legal protection after an incident or an accident, etcetera—all these things that some might take for granted today had to be fought for by our past colleagues.”

100 years of Air Traffic Control (1922-2022)—History, Stories, and Anecdotes by Philippe Domogala and Philip Marien will be published by IFATCA in October 2022 to coincide with the International Day of the Controller.

James “Jimmy” Jeffs considered the “father of air traffic control,” at London Croydon Airport around 1928.
James “Jimmy” Jeffs considered the “father of air traffic control,” at London Croydon Airport around 1928.

NATS Celebrates Centennial

It might be a little unusual to celebrate a centenary over two years, but the leading UK air traffic control organization, NATS, said in 2020 that it hoped its followers would permit a little creative ambiguity when it came to starting the celebrations.

“Major developments in early air traffic control occurred between 1920 and 1922, such that we think of this period as its inception point,” says NATS’s Paul Beauchamp. “Of course, it didn’t emerge fully formed, but the intent to aid the safety and efficiency of aircraft was clearly there among those early pioneers.”

While a dozen flights a day took off in 1920, now 2.6 million aircraft are controlled every year by NATS. But the blueprint laid down in places like Croydon Airport in the 1920s—where the first control tower was built—remains recognizable. “It is only now, 100 years later, that things like digital towers and satellite surveillance are rewriting that blueprint and ushering in a new era,” said Beauchamp.

As demand grew for air travel, it became clear that a more organized way of safely managing aircraft was essential, and so the development of a system of air traffic control began. It was an iterative process and nowhere was that more the case than at the UK’s designated primary “air port” in Croydon.

On Feb. 25, 1920, the UK Air Ministry gave approval for the construction of an “aerodrome control tower” at Croydon, to be “erected 15 feet above ground level” and with “large windows to be placed on all four walls”—a design that today remains recognizable. Croydon Airport opened in March 1920, taking over from Hounslow as London’s main airport, and the control tower was operational later that year.

The first controllers—known as civil aviation traffic officers or CATOs—and the radio officers who worked alongside them provided traffic and weather information to pilots over the radio or via a system of flags or lamps. Croydon also had what were called “direction finding” services beginning in 1920—using radio signals to find an aircraft’s bearing from the airport—and also perfected the more sophisticated system of wireless position fixing, which allowed the CATOs to triangulate the location of aircraft via the bearings from three radio receivers. The bearings were passed to Croydon where the aircraft’s position was manually calculated and passed back to the pilot.

Among the British ATC pioneers was James “Jimmy” Jeffs, a civil aviation traffic officer at London Croydon airport, who was one of the innovators in developing the discipline of air traffic control. Holder of the first-ever air traffic control license, Jeffs helped develop many of the systems and procedures that were approved by the UK Air Ministry. After establishing over 25 ATC units and the first controller training college, he led the establishment of the North Atlantic Airspace and the “track” system, which is only now becoming obsolete thanks to real-time satellite surveillance.

Another British pioneer was Fred “Stanley” Mockford. Moving from Morse code to radio telephony introduced the need for a new way to use language to ensure messages were clearly understood. A railway telegrapher, Mockford served in the Royal Flying Corps during World War I as part of a team developing ground-to-aircraft communication.

Mockford used that experience to help develop Croydon’s system of wireless position fixing. In 1923, Mockford conceived the distress phrase “Mayday, Mayday, Mayday” (based on the French word “m’aidez,” meaning “help me’), which was adopted as the international standard distress phrase in 1927.

The redevelopment of Croydon in the 1920s saw the construction of a second tower in 1923 and a third and final tower in 1928. The iconic square white tower—alongside the new terminal building—remained in operation until the airport closed in 1959.    z