ADS-B Explained: How Flight Trackers See Planes

Last updated: January 2025

When you open a flight tracking app and see thousands of planes moving across a map, you might wonder: how does this work? Where does the data come from? And why can't some planes be tracked?

This guide explains ADS-B — the technology that powers modern flight tracking — in plain English.

What Is ADS-B?

ADS-B stands for Automatic Dependent Surveillance–Broadcast. It's a technology that allows aircraft to automatically broadcast their position, altitude, speed, heading, and identity on a regular basis — typically every second.

Think of it like this: every equipped aircraft is constantly shouting out its location and flight details on a radio frequency that anyone with the right receiver can pick up.

How It Works

  1. The aircraft determines its position using GPS (Global Positioning System) — hence "dependent" in ADS-B
  2. The aircraft broadcasts this data on a standard radio frequency (1090 MHz in most of the world) — hence "broadcast"
  3. Ground receivers pick up the signal and relay it to online networks
  4. Apps and websites display the data on maps, showing you where every tracked aircraft is in real-time

Why "Automatic"?

Unlike older radar systems that required ground stations to actively ping aircraft, ADS-B is entirely passive from the ground's perspective. The aircraft does all the work — calculating its own position and broadcasting it continuously. This makes the system cheaper, more accurate, and capable of tracking far more aircraft than traditional radar.

The Global Receiver Network

ADS-B data is collected by a massive global network of receivers:

Together, these receivers create a near-global coverage map. In densely populated areas like the UK, Europe, and North America, coverage is excellent. In remote areas like oceans, deserts, and parts of Africa and South America, coverage can be patchy.

What Data Does ADS-B Provide?

When an aircraft broadcasts ADS-B data, it includes:

This is the same data that flight tracking apps like What Plane? use to show you the nearest aircraft.

Why Can't All Planes Be Tracked?

Not every aircraft broadcasts ADS-B data. Here's why:

Military Aircraft

Many military aircraft do not broadcast ADS-B, or broadcast limited data. Fast jets on training missions, military transport flights, and classified operations often remain invisible to civilian tracking apps. This is a deliberate choice for operational security.

Older Aircraft

Aircraft built before modern avionics requirements may not be equipped with ADS-B Out transponders. Some older general aviation aircraft — particularly small piston-engine planes — may not broadcast at all.

Private Jets with Data Blocking

In some countries, private jet owners can request that their data be filtered from public tracking platforms. The aircraft still broadcasts ADS-B for air traffic control purposes, but the data is anonymised or blocked from third-party apps.

Helicopters

Helicopter ADS-B equipment varies widely. Some broadcast continuously, others only under instrument flight rules (IFR), and some not at all.

Remote Areas

Even if an aircraft is broadcasting, it won't show up on a tracker if there are no ground receivers nearby to pick up the signal. Over oceans, deserts, and remote regions, coverage can be sparse.

ADS-B vs. Radar

Feature ADS-B Traditional Radar
Who calculates position? The aircraft (via GPS) The ground station
Coverage Global (where receivers exist) Limited to radar range (~200 nm)
Cost Low (receivers are cheap) High (large ground stations)
Accuracy Very high (GPS-level) Good, but degrades with distance
Update rate Every 1–2 seconds Every 4–12 seconds
Altitude data Yes (from aircraft) Sometimes (requires secondary radar)

ADS-B has largely replaced radar for civilian air traffic management in many parts of the world, and it's the primary data source for consumer flight tracking apps.

How What Plane? Uses ADS-B Data

What Plane? uses ADS-B data from the ADSB.lol network to detect aircraft within 30 nautical miles of your location. The app calculates 3D distance — combining horizontal distance and altitude — to find the truly closest aircraft, not just the one that appears nearest on a flat map.

The home screen widget shows the nearest aircraft at a glance: flight number, aircraft type, airline, altitude, speed, distance, and direction. No searching, no typing, no fiddling with maps.

Frequently Asked Questions

Is ADS-B data real-time? ADS-B data is near real-time, typically delayed by only a few seconds. The delay depends on how quickly ground receivers relay data to the network and how quickly the app fetches updates.

Can I set up my own ADS-B receiver? Yes. Projects like ADSB.lol and FlightAware provide guides and sell receiver kits. Many enthusiasts run receivers at home and contribute data to the global network.

Does ADS-B compromise privacy? ADS-B was designed for air traffic management, not public tracking. However, the data is broadcast on an open frequency and can be received by anyone. Some countries have introduced regulations around public display of ADS-B data, particularly for government and private aircraft.

Will ADS-B replace radar entirely? In many regions, ADS-B is already the primary surveillance method for civilian air traffic. However, radar remains important as a backup and for military operations.

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