ADS-B in Plain English

What is ADS-B? It stands for Automatic Dependent Surveillance-Broadcast, and in plain English it means this: a plane works out where it is using satellite navigation, then broadcasts that position into the air every second or so, for anyone with the right receiver to pick up. No radar, no question from air traffic control, no button the pilot has to press. That one mechanism, repeated by tens of thousands of aircraft a day, is the reason a flight-tracking map can show a plane moving in something close to real time. This guide breaks down the four words in the acronym, how ADS-B differs from the radar it is steadily replacing, how a tracking site actually gets the data, and why some patches of the map still look emptier than others.

The four words, decoded

Every letter in ADS-B is doing real work, and reading them in order explains the whole system.

Automatic means the broadcast happens on its own. No pilot has to key a microphone and no controller has to send a request; the equipment just keeps transmitting on a fixed schedule, the whole flight, without anyone triggering it (Wikipedia, "Automatic Dependent Surveillance–Broadcast," captured 2026-09-23).

Dependent means the position in that broadcast is not measured by whoever receives it. It depends entirely on the aircraft's own onboard navigation system working out its own position and reporting it honestly. A ground receiver, or another aircraft, is just picking up a number the plane already calculated for itself.

Surveillance is the aviation term for tracking where aircraft are and where they are going. ADS-B is one way of doing that job, sitting alongside (and increasingly replacing) radar for the same purpose.

Broadcast is the part that makes flight tracking possible at all. The signal is not addressed to one specific air traffic control tower the way a radio call is. It goes out to anyone within range who has the equipment to listen, which is exactly what lets a website with no relationship to any airline or air navigation authority put that aircraft on a public map.

How the aircraft knows where it is

The position an aircraft broadcasts comes from satellite navigation, GPS or another GNSS system, the same basic technology behind the navigation app on a phone (Wikipedia, "Automatic Dependent Surveillance–Broadcast," captured 2026-09-23). The aircraft's own equipment calculates its latitude, longitude and altitude from those satellite signals, packages that up with other data such as groundspeed, heading and identification, and transmits the whole package on a fixed cycle. Nothing about this needs contact with the ground. An aircraft flying over open ocean, far from any radar station, is still calculating and broadcasting its own position exactly as it would over a city; the only question is whether anything nearby is listening.

ADS-B Out vs. ADS-B In

The acronym covers two related but different things, and it is worth keeping them separate.

ADS-B Out is the transmitting half: the aircraft sending its own position, altitude and velocity out into the world. This is the half that makes an aircraft visible to ground receivers, to air traffic control, and to any tracking website.

ADS-B In is the receiving half: equipment on board an aircraft that picks up the ADS-B Out broadcasts from other nearby aircraft, giving the flight crew their own picture of surrounding traffic (Wikipedia, "Automatic Dependent Surveillance–Broadcast," captured 2026-09-23). A flight-tracking website is really just a ground-based version of ADS-B In: something other than an aircraft, listening to ADS-B Out broadcasts and turning them into a map.

Why ADS-B replaced (and supplements) radar

Traditional secondary surveillance radar works by interrogation: a ground station sends out a signal, an aircraft's transponder replies, and the station has to sweep around and ask again to get an updated position. ADS-B flips that around. Because the aircraft is broadcasting on its own schedule rather than waiting to be asked, a receiver gets a fresh position roughly once a second, which is faster and steadier than waiting for a radar sweep to come back around (Wikipedia, "Automatic Dependent Surveillance–Broadcast," captured 2026-09-23).

ADS-B runs on two different frequencies depending on the aircraft. Commercial and higher-performance aircraft, along with anything flying above 18,000 feet, use 1090 MHz Extended Squitter, usually shortened to 1090ES. Smaller general-aviation aircraft flying below 18,000 feet more commonly use 978 MHz on a system called the Universal Access Transceiver, or UAT, which can also carry weather and traffic information alongside the position data (Wikipedia, "Automatic Dependent Surveillance– Broadcast," captured 2026-09-23). A tracking site aiming to cover commercial air traffic is mostly listening on 1090ES.

This is not a hypothetical technology still on the drawing board. In the United States, ADS-B Out has been a legal requirement since 1 January 2020 for aircraft operating in Class A, B and C airspace, and in certain parts of Class E airspace too (Wikipedia, "Automatic Dependent Surveillance– Broadcast," captured 2026-09-23). Other countries have their own mandates on similar timelines. The short version: most of the commercial traffic a tracking site would want to show is already required to be broadcasting.

How a flight-tracking site actually gets this data

None of this reaches a website by magic. Somewhere, a physical antenna has to be within line-of-sight range of the aircraft, tuned to the right frequency, to actually pick up the broadcast. A number of flight-tracking sites run on exactly that: crowd-sourced, distributed networks of ADS-B ground receivers, frequently including personal receivers set up by aviation enthusiasts, feeding what they hear back to a central service that builds the map (Wikipedia, "Automatic Dependent Surveillance–Broadcast," captured 2026-09-23). That is also why "who is listening near you" matters as much as "what the aircraft is broadcasting."

Why some parts of the map look empty

Because a ground receiver's range depends on physical line of sight, distance, and interference from weather or obstacles between it and the aircraft, coverage is not the same everywhere (Wikipedia, "Automatic Dependent Surveillance–Broadcast," captured 2026-09-23). Near cities and busy air corridors, such as Delhi or Dubai, where there are plenty of ground receivers close together, a map can look dense with aircraft. Out over open ocean or in remote regions with no ground station for hundreds of miles, an aircraft can be broadcasting its ADS-B Out signal perfectly and still be invisible to a ground-based tracking network, simply because nothing nearby is positioned to hear it. This is a property of how ground-receiver ADS-B works everywhere, not a flaw specific to any one tracker.

It is also the reason satellite-based ADS-B exists at all: payloads carried on low-Earth-orbit satellites can pick up the same broadcasts from space, extending surveillance out over ocean and remote areas that ground stations simply cannot reach (Wikipedia, "Automatic Dependent Surveillance– Broadcast," captured 2026-09-23). That a purpose-built satellite system had to be developed to close this gap is itself the clearest evidence that the gap is real: a ground-receiver network, on its own, only ever sees as far as its receivers do.

How TrackMyWings helps

TrackMyWings™ is a live flight-tracking platform in development, India-first in go-to-market with worldwide coverage. A private beta shipped on 2026-08-24: Android only, on the Play internal testing track, with a small group of named testers. The wider product, including a live flight tracking view for the people waiting on someone's flight and aircraft tracking by tail number, is planned for launch rather than available today, and public launch has no fixed date. Understanding how ADS-B actually works, and where its honest limits are, is exactly the kind of thing worth knowing before trusting any dot on any map.

Questions people ask

What does ADS-B stand for? Automatic Dependent Surveillance-Broadcast: automatic because it needs no pilot or ATC trigger, dependent because it relies on the aircraft's own navigation for position, surveillance because it is a way of tracking aircraft, and broadcast because it goes out to anyone in range rather than one recipient.

How does a plane using ADS-B know its own position? From satellite navigation, GPS or another GNSS system, the same basic technology behind a phone's navigation app. The aircraft calculates its own position and includes it in the broadcast.

What is the difference between ADS-B Out and ADS-B In? ADS-B Out is the transmitting side: an aircraft sending its position, altitude and velocity. ADS-B In is the receiving side: equipment that picks up other aircraft's ADS-B Out broadcasts, whether that equipment is on another plane or on the ground.

Why doesn't ADS-B need radar? Radar has to interrogate an aircraft and wait for a reply, then sweep around and ask again. ADS-B aircraft broadcast on their own schedule, roughly once a second, without waiting to be asked, which is why it can update faster and more steadily than a radar sweep.

Why do some flight-tracking maps show gaps over the ocean? Ground-based ADS-B receivers only pick up a signal within line-of-sight range. Far from land and ground stations, an aircraft can be broadcasting normally and still go unheard, which is why satellite-based ADS-B was built specifically to cover the same gap from space.

Sources

• Wikipedia, "Automatic Dependent Surveillance–Broadcast": https://en.wikipedia.org/wiki/Automatic_Dependent_Surveillance–Broadcast, captured 2026-09-23