What Is ADS-B and How Does Aircraft Tracking Work?

Every time you watch a plane move across a flight tracker, you are seeing a technology called ADS-B at work. It is the backbone of modern flight tracking, and it is simpler than it sounds. This explainer covers what ADS-B is, how it works, and why it makes so much flight data freely available.

What ADS-B stands for

ADS-B stands for Automatic Dependent Surveillance, Broadcast. Breaking that down:

• Automatic: it transmits on its own, without being interrogated.
• Dependent: it depends on onboard navigation, primarily GPS.
• Surveillance: it is used to monitor and track aircraft.
• Broadcast: the signal is sent out openly for anyone to receive.

In plain terms: the aircraft figures out where it is and tells everyone, constantly.

How ADS-B works, step by step

The process is straightforward:

1. The aircraft determines its position. Modern aircraft use GPS to know exactly where they are.
2. It broadcasts a message. Several times a second, the aircraft transmits its identity, position, altitude, speed, and heading.
3. Ground receivers listen. Receivers on the ground, run by aviation authorities, companies, and hobbyists, pick up these broadcasts.
4. Trackers combine the data. Services collect receiver data and plot the aircraft on a live map.

That is the whole loop. Because the aircraft broadcasts openly, the system is wonderfully simple compared with older radar.

What information ADS-B carries

A single ADS-B broadcast can include:

This is exactly the information a flight tracker needs to show you what is overhead. Our guide on what plane is flying over your house shows how to read it.

Why ADS-B makes data free

Here is the key insight: an ADS-B signal is an open radio broadcast. It is not encrypted or locked down. That means anyone with a suitable, inexpensive receiver can pick up the aircraft overhead.

A global community of enthusiasts runs receivers and shares the data, which is why so much flight tracking is available free of charge. PlaneTicker uses this open ADS-B data, which is why there is no subscription. We explain this further in how flight tracking works without a subscription.

Limitations of ADS-B

ADS-B is excellent, but it has limits:

• Line of sight. The signal travels in a straight line, so terrain, buildings, and the curvature of the Earth can block it over long distances. Coverage depends on receivers being within range.
• Not every aircraft broadcasts. Some military, government, and older aircraft do not transmit public ADS-B. We cover this in why you cannot see military or private jets.
• It is dependent on GPS. If onboard navigation is unavailable, position reporting is affected.

To fill gaps, trackers sometimes combine ADS-B with other techniques, which we compare in ADS-B vs radar vs MLAT.

From signal to display

The beauty of ADS-B is that it turns the invisible traffic above you into something you can watch. A flight tracker display like PlaneTicker Desktop takes this open data and renders the aircraft over your location in real time, with callsign, altitude, airline, and route. You can try the experience free in the browser demo.

In short

ADS-B is the reason live flight tracking exists in the form it does today: aircraft broadcasting their own position, openly, several times a second, for anyone with a receiver to pick up. It is elegant, accurate, and, crucially, open, which is what makes free flight tracking possible.