ADS-B vs MLAT vs FLARM vs TIS-B — Position Sources Explained
Click an aircraft on FlyRadar and you'll see a colored ring around it. That ring isn't decoration — it tells you how the aircraft's position was determined. There are four different technologies at work, and they vary a lot in accuracy and coverage.
ADS-B — the gold standard
An ADS-B position comes straight from the aircraft itself: its own GPS fix, broadcast over radio. It's the most accurate source — typically within meters — and updates every second or so. If an aircraft has a modern transponder and is in receiver range, this is what you get. (More detail in What is ADS-B?)
MLAT — triangulation for older transponders
Multilateration solves a problem: aircraft with older Mode S transponders respond to interrogations but don't broadcast their GPS position. MLAT receivers don't get told where the aircraft is — instead, four or more receivers at known locations each timestamp the same transponder reply. Because radio travels at a fixed speed, the tiny differences in arrival time reveal the aircraft's position mathematically.
- Needs at least 4 receivers hearing the same signal
- Accuracy of tens to hundreds of meters — good, but noisier than ADS-B
- This is why aircraft "jitter" more in dense coverage areas — MLAT positions jump around slightly
FLARM — the glider network
FLARM (from "flight alarm") is a collision-warning system built for gliders, sailplanes, towplanes and helicopters. It broadcasts position on a different protocol and frequency, primarily across Europe. Gliders are small, often lack transponders entirely, and fly in mountainous areas — FLARM fills the gap. FlyRadar ingests FLARM data via the Open Glider Network (OGN), which is why you can watch sailplanes ridge-soaring in the Alps that no conventional tracker shows.
TIS-B — radar, rebroadcast
Traffic Information Service – Broadcast is an FAA service: ground radar detects an aircraft, and the position is rebroadcast on ADS-B frequencies so equipped aircraft (and trackers) can see it. It only exists in US airspace and appears when an aircraft is visible to FAA radar but isn't broadcasting ADS-B itself.
Why it matters when you watch the map
- Smooth vs jumpy trails — ADS-B produces clean trails; MLAT can look like small hops.
- Disappearing aircraft — an MLAT-tracked plane dropping below 4-receiver coverage simply vanishes, even though it's still flying.
- Gliders over Europe — FLARM contacts are often the only aircraft visible in alpine valleys.
See it live: open the map, zoom into any busy area, and compare the ring colors across aircraft.