Flight Tracking Technology

The engineering behind the map: ADS-B, radar, multilateration, satellites and the receivers that hear it all.

Every aircraft icon gliding across a flight tracking map is the end of a long technical relay. A transponder in an aluminum bay behind the cockpit composes a digital message, a quarter-wave antenna flings it out at 1090 MHz, and somewhere below, a receiver on a rooftop or a satellite 485 miles up catches it, timestamps it and passes it on. This hub is about that relay: the physics, the protocols and the surprisingly large role that ordinary hobbyists play in keeping the picture alive.

The foundation of it all is Automatic Dependent Surveillance-Broadcast, and our deep dive into how ADS-B powers modern flight tracking is the best place to start. From there the story branches. Air traffic controllers still lean on older, radio-echo techniques, explained in our guide to primary and secondary surveillance radar. When an aircraft transmits but withholds its position, tracking networks fall back on multilateration, the art of locating planes by timing alone. And over the oceans, where no ground antenna can hear anything, a constellation of satellites now listens instead; we tell that story in our piece on satellite flight tracking across the oceans.

The category also decodes the language aircraft speak. You will learn what a squawk code is and why 7500, 7600 and 7700 make controllers sit up straight, how the Mode S protocol gives every airframe on Earth a unique 24-bit digital fingerprint, and where the data on public tracking sites actually comes from, feed by feed. If you would rather build than read, the final guide walks you through assembling your own ADS-B receiver with a Raspberry Pi for less than the cost of a nice dinner.

Why does any of this matter? Because understanding the plumbing makes you a sharper user of the map. Once you know that ADS-B is line-of-sight, you understand why coverage thins over mountains. Once you know what MLAT needs to work, you understand why some business jets show no altitude. Once you know how satellite reception differs from terrestrial reception, oceanic position jumps stop looking like glitches. Open the live flight map in one tab and these guides in another, and the icons stop being dots and start being decodable signals. For a sense of scale, our flight statistics dashboard shows just how many aircraft this global listening system is following at once, typically well over ten thousand in the busiest hours of the day.

Quick entry points

Use these guides as direct routes into the subject, or browse the complete collection below.

Why Your Flight Took a Weird Route: Great Circles, Jet Streams and ETOPS: That curved line on the tracker is not a detour. Here is why the shortest path looks bent, why the return leg takes longer, and what really pushes an aircraft off the straight line.
Build Your Own ADS-B Receiver With a Raspberry Pi: For under a hundred dollars, a Raspberry Pi and a USB radio dongle can hear every airliner within 200 miles. A complete, honest build guide for beginners.
Where Flight Tracking Data Comes From: Feeds, Networks and APIs: That smooth aircraft icon is really a braid of ADS-B receivers, MLAT servers, satellites, schedules and government feeds. Here is the supply chain of the map.

All guides in this hub

Flight Tracking Technology Why Your Flight Took a Weird Route: Great Circles, Jet Streams and ETOPS That curved line on the tracker is not a detour. Here is why the shortest path looks bent, why the return leg takes longer, and what really pushes an aircraft off the straight line. Flight-Tracker.net Editorial Team 7 min read

Flight Tracking Technology Build Your Own ADS-B Receiver With a Raspberry Pi For under a hundred dollars, a Raspberry Pi and a USB radio dongle can hear every airliner within 200 miles. A complete, honest build guide for beginners. Flight-Tracker.net Editorial Team 8 min read

Flight Tracking Technology Where Flight Tracking Data Comes From: Feeds, Networks and APIs That smooth aircraft icon is really a braid of ADS-B receivers, MLAT servers, satellites, schedules and government feeds. Here is the supply chain of the map. Flight-Tracker.net Editorial Team 7 min read

Flight Tracking Technology Mode S and ICAO 24-Bit Addresses: Every Aircraft's Digital Fingerprint Beneath every callsign and registration lies a permanent 24-bit hex address, one of 16.7 million. Here is how Mode S gave every aircraft a digital fingerprint. Flight-Tracker.net Editorial Team 8 min read

Flight Tracking Technology Transponders and Squawk Codes: 7500, 7600, 7700 Explained Every flight wears a four-digit radio badge called a squawk code, and three of them make every controller's screen light up. Here is the system explained. Flight-Tracker.net Editorial Team 7 min read

Flight Tracking Technology Satellite Flight Tracking: Following Planes Across Oceans Until 2019, planes over oceans were invisible to trackers. Then 66 satellites started listening to 1090 MHz from orbit. Here is how space-based ADS-B works. Flight-Tracker.net Editorial Team 7 min read

Flight Tracking Technology Multilateration (MLAT): Tracking Planes That Don't Want to Be Found MLAT locates aircraft that broadcast no position, using nothing but nanosecond timing across four or more receivers. Here is the math and the magic behind it. Flight-Tracker.net Editorial Team 7 min read

Flight Tracking Technology Primary vs Secondary Radar: How Air Traffic Control Sees Planes Air traffic control still relies on two very different radars: one that hears echoes off metal, and one that asks the aircraft to answer. Here is how both work. Flight-Tracker.net Editorial Team 8 min read

Flight Tracking Technology ADS-B Explained: The Technology That Powers Flight Tracking ADS-B is the radio protocol behind nearly every flight tracking map. Here is how it works, why regulators mandated it, and what those 1090 MHz messages contain. Flight-Tracker.net Editorial Team 8 min read

Flight Tracking Technology: Common questions

What is ADS-B?

Automatic Dependent Surveillance-Broadcast. The aircraft determines its own position by GPS and broadcasts it in the clear, rather than waiting to be found by a radar sweep. It is the backbone of modern flight tracking and of air traffic surveillance generally.

How is radar different from ADS-B?

Radar finds aircraft by bouncing radio energy off them or by interrogating a transponder, and it works whether or not the aircraft cooperates. ADS-B depends on the aircraft broadcasting accurate data about itself, which is why the two are used together.

What is multilateration?

MLAT calculates an aircraft's position from tiny differences in the time its transponder signal reaches several receivers. It works for aircraft that have a transponder but no ADS-B position, filling gaps the newer system leaves.

How are flights tracked over the ocean?

Increasingly by satellite. Receivers in orbit pick up the same ADS-B broadcasts far from any land-based receiver, which is why coverage over open water has improved dramatically and why oceanic separation has been able to shrink.

What does the flight tracking technology hub cover?

9 guides, from “ADS-B Explained: The Technology That Powers Flight Tracking” to “Why Your Flight Took a Weird Route: Great Circles, Jet Streams and ETOPS”. Each one is written by a named author and cites sources you can check yourself.