Every aircraft on the live radar put itself there. None of it comes from a radar dish we own — it arrives as unencrypted broadcasts from the aircraft themselves, picked up by receivers on the ground. That single fact explains most of what people find puzzling about flight tracking: why some aircraft never appear, why coverage has odd notches in it, why a transatlantic flight seems to freeze halfway across the ocean.
These pages are written for people watching the map rather than for people flying. There is no prior knowledge assumed, and nothing here requires you to buy anything — though one guide covers what it takes if you decide you want a receiver of your own.
Start here
What is ADS-B?
How aircraft broadcast their own position on 1090 MHz, what is actually in the messages, and the real reasons some aircraft never show up on any tracker.
How to read the radar
Callsigns, hex codes, flight levels, ground speed and vertical rate — every field on the aircraft panel, including the two that quietly mislead you.
Squawk codes explained
Why there are exactly 4,096 of them, what 7500, 7600 and 7700 really mean, and the routine UK codes you will see constantly.
The airspace you're watching
Swanwick, the London TMA, the four Heathrow holding stacks, and how airspace classes shape the patterns on the map.
Build your own receiver
What to buy, what it costs, and why almost everyone spends their money on the wrong component.
If you only read one thing
The most useful single idea is the difference between a callsign and a hex code. The callsign is the flight — it changes daily, and it is what the crew typed in before departure. The hex code is the aircraft — a 24-bit address burned into the transponder that stays with the airframe for its working life.
Once that distinction is clear, everything else on a tracker falls into place: why the same aeroplane appears under different names on different days, why the airline logo is sometimes wrong, and why serious enthusiasts always quote the hex.