No single source covers every aircraft everywhere, so what you see on a flight map is the result of combining several and deciding which to trust at each moment. This guide describes how flight tracking works across the industry in general; it is not a list of the sources any particular provider uses.
The main data sources
| Source | What it provides | Coverage | Limits |
|---|---|---|---|
| ADS-B, ground receivers | Position, altitude, speed, heading and identity, broadcast by the aircraft itself | Wherever a receiver is within line of sight: most land areas with air traffic | Gaps over oceans, deserts, polar routes and at low altitude far from receivers |
| ADS-B, satellite receivers | The same broadcasts, received from space | Global, including oceans and remote areas | Fewer messages per minute than dense ground networks |
| MLAT (multilateration) | A calculated position for aircraft that transmit but don’t broadcast their position | Where several ground receivers hear the same aircraft | Needs at least four receivers; less precise than ADS-B |
| Schedules | Flight numbers, routes and planned times | Every scheduled flight | Plans, not positions; flights change on the day |
| Airline operational data | Actual departure and arrival times, gates, delays | Depends on the airline and data partner | Not a position source |
ADS-B: the aircraft says where it is
ADS-B (Automatic Dependent Surveillance–Broadcast) is the backbone of modern flight tracking. An equipped aircraft works out its own position by satellite navigation and broadcasts it — with altitude, speed, heading and identity — about once a second on 1090 MHz. Anyone with a suitable receiver can pick it up; nothing has to ask the aircraft.
Most airliners are required to carry it. In the United States, aircraft flying in most controlled airspace have needed ADS-B Out since January 2020. In Europe, the requirement covers aircraft flying under instrument flight rules that weigh more than 5,700 kg at take-off or cruise faster than 250 knots. As a result, almost every airliner broadcasts ADS-B.
Ground receiver networks
Ground receivers hear aircraft within line of sight: at cruise altitude that can be a few hundred kilometres, near the ground much less. Thousands of receivers, many run by volunteers and enthusiasts, cover most land areas where airlines fly. Coverage thins out over water, deserts, mountains and polar regions, and at low altitude away from airports.
Satellite ADS-B
Receivers on low-earth-orbit satellites pick up the same broadcasts from space. This closes the biggest gap in ground networks — oceans and remote areas — where a flight would otherwise disappear between the last receiver on one coast and the first on the other.
MLAT: locating aircraft that don’t report a position
Some aircraft transmit identity and altitude but not their position. When at least four ground receivers hear the same signal, the small differences in when it reached each receiver can be used to calculate where the aircraft is. This is multilateration (MLAT). It works only where receivers are dense enough, and its positions are less precise than ADS-B.
Schedules and airline data
Positions alone don’t say that an aircraft is flight XY123 from one city to another, or when it is due to land. Schedule data provides flight numbers, routes and planned times. Airline operational data adds what actually happened: when the aircraft left the gate, took off, landed and reached the gate (often called OOOI times: Out, Off, On, In), plus gates and delays.
Putting it together
A flight tracker continuously matches positions to flights, decides which source to trust when they disagree, and keeps each flight on the map through short gaps in coverage. When no fresh position arrives for a while, a good tracker says so instead of showing an old position as if it were live.
How fresh is “live”?
Aircraft broadcast about once a second, but what a passenger or an application sees depends on how often the tracker refreshes, how dense receiver coverage is along the route, and whether the flight is over an area with gaps. The useful question is not only “how often does it update?” but “how old is this position right now?” — which is why freshness should be visible, not hidden.
How Wireum uses this
Wireum Map and the Wireum Data API show live aircraft positions from ADS-B sources, refreshed every 5 seconds for an airline’s entire fleet. Every flight carries a freshness state — live, stale (position briefly not updated) or signal-lost (no recent position) — and the age of its last position in seconds, so passengers and applications always know how current a position is.