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  • Writer's pictureSimon Golstein

Aircraft that self-report: the power of ADS-B

Before 2009, whenever an aircraft flew over Hudson Bay in Canada, it disappeared from radar screens. This equaled approximately 35,000 flights a year between various destinations in Europe and North America that were left without air traffic control support for hours.

What changed? In May 2009, Nav Canada, the operator of Canada's civil air navigation system, Canada’s airspace regulator, implemented a technology called ADS-B over this airspace. From this point on, the authority could accurately track airplanes over the entire 250,000 square nautical mile-area, as well as maximize efficiency by reducing separation standards.

In this article, we’ll look at ADS-B technology, the effect it’s had on aviation, and what the future holds.

What is ADS-B?

ADS-B stands for automatic dependent surveillance broadcast. Automatic because it doesn’t require pilot input, dependent because it’s dependent on satellite-based navigation, surveillance because it provides data for surveillance purposes, and broadcast because it sends this data out every half second so any integrated device can detect it.

Just like radar, ADS-B is a simple concept. While radar sends out signals and collects those that bounce back, ADS-B lets airplanes send their own information out, both to ground stations and other aircraft, with no need for interrogation by an external system.

ADS-B supplements the limitations of radar and may one day replace it entirely.

What’s wrong with radar?

Radar is the pillar of our current air traffic management systems. Gradually integrated into air traffic management (ATM) systems since the Second World War, it enables air traffic controllers to coordinate enormous amounts of air traffic and without it, the aviation industry as we know it would never have been possible. Broadly speaking, air traffic is controlled by two types of radar: primary radar sends out radio waves and detects anything that bounces them back, while secondary radar targets aircraft-mounted transponders which respond to these interrogations.

Radar has limitations. There are technical limitations like effectiveness being limited by natural obstacles, and installations configured to detect aircraft struggling with ‘clutter’ like small aircraft, birds and drones. But the main issue is coverage. Many places lack radar infrastructure, and if there are no radar installations, there’s no radar. For example, radar range typically stretches around 200 nautical miles into the ocean, beyond which aircraft are on their own. Even on land, many remote areas have heavy air traffic but lack radar infrastructure. Take Alaska in the US - a huge, sparsely populated state where as much as 80% of communities aren’t connected to the road system. Small aircraft are used heavily, but much of the state is uncontrolled airspace where pilots fly in unpredictable weather and mountainous terrain with no information or coordination from ATC. As a result, it is notorious for aviation accidents - in 2016, more than 42 percent of US aviation fatalities happened here.

Once ADS-B was introduced in Alaska, equipped aircraft quickly showed a 47 percent decline in accidents compared to non-equipped aircraft.

A marked improvement

ADS-B overcomes many of the limitations of radar. Because ADS-B transponders collect information from the Global Navigation Satellite System (GNSS), position and velocity data is far more accurate, and they broadcast this data every half second, which is more frequently than most radar systems. This more accurate guidance means better coordination, so more planes can fly safely at the same time with smaller procedural separation. In addition, less time wasted circling or flying at suboptimal altitudes means less fuel wasted and lower carbon emissions. ADS-B also provides more information than radar does. The broadcasts can include the flight callsign, ICAO aircraft address, latitude and longitude, altitude, rate of decent and ascent, velocity, emergency status (when activated), and more. Finally, ADS-B ground stations have more coverage than radar because they are cheaper to set up - the FAA has reported saving around $28 million a year in radar maintenance costs thanks to ADS-B.

ADS-B supplements traffic collision avoidance (TCAS) systems too - as long as the aircraft are equipped with ADS-B In.

ADSB Out and ADSB In

There are two types of ADS-B: ADS-B Out and ADS-B In.

ADS-B Out is the principal component of the system, broadcasting the aircraft’s information as detailed earlier via transponders that operate at 978 or 1090 MHz.

ADS-B In refers to equipment that can receive these signals. When an aircraft is equipped with ADS-B In, it receives direct signals from ADS-B Out-equipped aircraft and can also receive Flight Information System Broadcast (FIS-B) and Traffic Information Service (TIS-B) data. ADS-B In also serves to supplement traffic collision avoidance systems (TCAS). TCAS, in effect since the early 1980s, are based on transponders and use conflict detection algorithms to prevent collisions. They don’t rely on ADS-B broadcasts, but when compatible, ADS-B data enhances their performance.

Generally, ADS-B In is recommended but not compulsory. ADS-B Out, however, is required in most major regulated airspaces. In the US, for example, it’s required at 10,000 feet and higher, at all heights in B and C airspaces, and while flying within 12 nautical miles off the coast of the Gulf of Mexico at or above 3,000 feet. Other countries that have made ADS-B mandatory include most members of the European Aviation Safety Agency, Australia, New Zealand, France, Canada, India, China, Singapore, throughout South America… the list goes on.

ADS-B and drones

One of the reasons that ADS-B became necessary was the economic boom of the 1980s that led to a rapid growth in vacations and air traffic. Today, we are seeing another significant growth in air traffic - but this time it’s because of uncrewed aircraft. Until fairly recently, UAVs were not subject to the same regulatory demands as crewed aircraft, or indeed many regulatory demands at all. But this is changing fast as these new aircraft take on more roles in industry and society, including for personal transport.

Drones already have their own form of ADS-B, called Remote ID, and their own form of air traffic control networks, called uncrewed traffic management (UTM). Both of these systems are currently only partially enforced, but steadily coming into force. ADS-B integration was not an immediate requirement because ADS-B is usually not used at low altitudes where drones operate, but the exponential growth of drone traffic and the advent of eVTOLs for personal transport has necessitated their inclusion into existing air traffic management systems. For example, dominant drone producer DJI has integrated ADS-B In into all its 250g+ drones since 2020, enabling drone pilots to receive notifications about nearby aircraft.

Similarly, it is expected that UTM networks have ADS-B In capabilities so that they can effectively coordinate UAVs traffic with crewed aircraft. High Lander’s Vega UTM, for example, has ADS-B In capabilities via Pingstation 3.


ADS-B can be seen as an evolutionary step forward for air traffic management, coming at a time when air traffic was expanding rapidly. Today, when a whole new class of aircraft is causing air traffic to expand even further, ADS-B has a chance to prove its worth all over again.

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