What Is ADS-B?
ADS-B (Automatic Dependent Surveillance–Broadcast) is a system in which an aircraft works out its own position using satellite navigation and automatically broadcasts it to anyone listening. It is the main source of data for public flight trackers.
How it works
The aircraft’s GPS receiver calculates its position. A transponder then broadcasts a short message on 1090 MHz about once or twice a second. “Automatic” means the pilot does not need to do anything; “dependent” means it depends on the aircraft’s own navigation; “broadcast” means it is sent to everyone, not to one receiver.
What an ADS-B message contains
- The aircraft’s unique 24-bit address (see ICAO 24-bit address)
- Latitude, longitude and altitude
- Ground speed, heading and vertical rate
- The callsign and, on request, the squawk code
- Information about the quality of the position data
Who can receive it
Anyone with an inexpensive radio receiver and antenna can decode ADS-B. Thousands of volunteers do, and share the data with networks. That is why flight tracking has grown so quickly. You can join: read how to build an ADS-B receiver.
ADS-B Out and ADS-B In
“ADS-B Out” means transmitting. “ADS-B In” means an aircraft receiving other aircraft’s broadcasts to show traffic to the crew. Trackers use only the Out signals.
Limits
- Not every aircraft has ADS-B. Older or small aircraft may not, and some military aircraft do not transmit.
- Range is line of sight, so mountains and the curve of the Earth limit what a receiver hears. Low aircraft are heard only from short distances.
- The position is as good as the aircraft’s GPS and is shown only after it passes through the network. See how accurate is flight tracking.
Where you see ADS-B on this site
Every plane on the live map is positioned from ADS-B (and some from MLAT). Look up the term in the glossary.
General information only, not legal or safety advice. Details change; check with your airline and the relevant authority. See our editorial policy.