How Aircraft Tracking Works
Ever wondered how flight radar sites know where every plane is? This guide explains the full pipeline: from aircraft transponder to your screen.
The tracking pipeline
Each section below explains one step in this pipeline.
What is ADS-B?
ADS-B (Automatic Dependent Surveillance-Broadcast) is the technology that makes modern aircraft tracking possible. Unlike traditional radar, which bounces radio waves off aircraft, ADS-B relies on planes themselves to broadcast their position.
Aircraft equipped with ADS-B transponders transmit short data packets on 1090 MHz. Each message includes the aircraft's GPS-derived position, altitude, speed, heading, and a unique identity code. These signals go out several times per second. No ground station needs to "ask" where the plane is.
Detection range
Because ADS-B signals travel line-of-sight, a plane cruising at 35,000 ft can be detected by receivers up to 400+ km away. Aircraft on approach or departure are typically picked up from 50-100 km.
Since 2020, ADS-B Out has been mandatory for aircraft flying in most controlled airspace in the US and Europe. Adoption is high across commercial aviation worldwide.
What's in each ADS-B message?
- ICAO 4006F3 Unique 24-bit aircraft ID
- LAT/LNG 51.47°N 0.45°W Position from GPS
- ALT 34,000 ft Pressure altitude
- SPD 487 kts Ground speed
- HDG 285° Track angle
- IDENT BAW287 Callsign / flight number
Broadcast every ~0.5s, picked up by any nearby receiver.
How tracking networks work
Thousands of ground-based receivers around the world capture ADS-B broadcasts and feed data into central servers. Services like Flightradar24, FlightAware, and OpenSky merge, deduplicate, and enrich it, then apps and displays consume the result via APIs.
Ground receivers
Amateur and commercial SDR receivers pick up 1090 MHz broadcasts and stream the decoded data over the internet to aggregator servers. Coverage is especially dense over Europe, North America, and parts of Asia.
Data aggregation
Multiple receivers often pick up the same aircraft. Aggregators merge and deduplicate reports, then enrich the raw position data with flight plans, aircraft registration databases, airline logos, and route information.
Apps and displays
The enriched data is served via APIs to apps like Flightradar24, dedicated flight tracker displays, and aviation tools. The same underlying data powers everything from your phone to a dedicated desk display like AvClock.
Refresh rate: Commercial tracking APIs update every 5-15 seconds for live aircraft. AvClock polls the data on a short cycle and updates your display the moment a new aircraft enters or leaves your detection zone.
How displays show aircraft overhead
A flight tracker display takes the same ADS-B-derived data and presents it in a format suited to your desk. Instead of a global map, it filters aircraft by your location and viewing direction, so you only see the planes you can actually look up and spot.
You set your coordinates and compass bearing once during setup. The display then applies a geometric filter: given your position, the aircraft's position, and your specified arc and radius, it calculates in real time which aircraft sit within your personal "window to the sky."
That's how AvClock turns raw global tracking data into a personalised desk display. The underlying technology is identical to Flightradar24. The difference is presentation: an always-on, glanceable clock that shows your sky, not the world.
Flightradar24 vs. AvClock
See it on your desk
AvClock uses the exact ADS-B pipeline described above to show you live aircraft from your own window. Hand-built in the UK, one-time payment.
Common questions
Frequently asked questions
Modern flight radar uses ADS-B: aircraft broadcast their position, altitude, and speed on 1090 MHz, ground receivers capture the signals, and networks aggregate and display them. See the pipeline above for the full flow from aircraft to your screen.
Planes transmit position and flight data via ADS-B transponders several times per second. Ground stations and amateur receivers pick up these broadcasts and send them over the internet to tracking networks. No interrogation of the aircraft is needed.
ADS-B (Automatic Dependent Surveillance-Broadcast) is the process of receiving and decoding the 1090 MHz broadcasts that aircraft transmit. This decoded data (position, speed, heading, identity) powers Flightradar24, FlightAware, and dedicated displays like AvClock.
Most commercial airliners and many general aviation aircraft broadcast ADS-B and appear on tracking sites. Some older or very light aircraft may not be equipped. Military aircraft sometimes operate with reduced or no ADS-B, which is why they occasionally disappear from tracking maps.
Both use the same ADS-B data. The difference is presentation and purpose: Flightradar24 shows you the entire world on an interactive map you have to open. AvClock is a physical, always-on desk display that shows only the aircraft visible from your specific window. Set once, then just glance up.
Military aircraft that operate with ADS-B enabled will appear. Many, however, operate with transponders off or in modes that are not publicly accessible. Tracking civilian commercial traffic is where ADS-B coverage is most comprehensive.
Now you know how it works.
See it on your desk.
AvClock is a dedicated flight tracker display that shows live aircraft visible from your window. Always on. No app. No subscription.
£269.00 one-time payment