Why Flight Tracker Routes Are Often Wrong
ADS-B carries position, altitude, speed and a callsign — not the origin or destination. Every route a flight tracker shows is a separate database lookup, which is where trackers differ. Free route databases go stale at the twice-yearly IATA season change, which is the commonest cause of a wrong destination.
Here is something most people never find out: the aircraft overhead is not telling anyone where it is going. An ADS-B broadcast carries position, altitude, speed, heading and a callsign — and nothing else. There is no origin in it and no destination.
So every tracker that shows you "London Heathrow → Málaga" has gone and looked that up somewhere, using the callsign as the key. The position is measured. The route is a database lookup — and that is where trackers quietly differ from one another.
Where route data actually comes from
There are three places to get it, and they are not equally good.
Free community databases. Volunteer-maintained mappings of callsign to city pair, built up from historical observations. They are free, easy to plug in, and they are what most hobby projects and a good many products use. Their weakness is structural: they record what a flight number used to do.
Airline schedule feeds. Accurate at the moment of publication, but a schedule is a plan. It does not know that today's aircraft went tech and the flight was cancelled, retimed or re-routed.
Commercial flight-data APIs. Paid services that reconcile schedules against what is actually flying. They cost real money per lookup, which is exactly why plenty of products do not use them.
Why free route databases go stale
Four things break them, and all four happen constantly.
The season change. Airlines republish their schedules twice a year, at the IATA season boundaries — summer runs late March to late October, winter late October to late March. Flight numbers get reassigned to different city pairs wholesale. A database that cached the old pairing and never refreshed keeps serving it, confidently, for months.
Flight numbers are reused. The same number is routinely flown on different city pairs on different days of the week, and after an airline merger inherited numbers can belong to a completely different part of the network.
Both legs share a number. Most short-haul flight numbers cover the outbound and the return on the same day. If a database stores the pairing without knowing which leg is currently airborne, it shows the journey backwards about half the time. If you have ever seen a plane "arriving" from the airport it clearly just left, that is what happened.
Some flights have no route at all. A police helicopter, an air ambulance or a military transport is not operating a scheduled service between two airports. There is no city pair to find. A tracker that fills the gap anyway is not reading data, it is guessing.
| Route source | Accuracy | Main weakness |
|---|---|---|
| Free community databases | Variable | Records what a flight number used to do |
| Airline schedule feeds | Good at publication | A plan, not what actually flew |
| Commercial flight-data API | High | Costs money per lookup |
| No source (guessed) | None | Invents routes for aircraft that have none |
What NearestPlane does about it
We used a free route database early on. It returned stale historical data and customers saw wrong destinations, so we removed it entirely rather than paper over it. Every airline callsign now goes to a paid commercial flight-data API, and that is the only source of route truth on the system.
On top of that source there are four deliberate choices:
- Routes expire at the IATA season boundary, not on a fixed timer. A cached route is valid for exactly as long as the schedule it came from, and no longer.
- Airlines with inconsistent data get a shorter life. Where an operator is known to shuffle flight numbers between city pairs, its routes are held for hours rather than a season, so a stale one corrects itself within half a day.
- Callsigns that cannot have a route are never given one. Air ambulances, police units and military transports are recognised and excluded from route lookup altogether, so the display says nothing rather than something invented.
- Reported errors are purged, not argued with. When a customer tells us a route looked wrong, the cached entry is removed so the next lookup starts clean.
The same principle runs through the rest of the data. There are 5,870 airlines in the database, 6,222 airport cities and 7,917 airport positions, so an operator code resolves to the airline's real name and brand colour, an airport code resolves to the city a person recognises, and a distance is measured from the actual airport rather than a rounded grid square.
How to check your own tracker
You do not have to take anyone's word for this, including ours. Pick an airliner going over, note the callsign and the route your tracker shows, then look that flight number up on the operating airline's own timetable — the airline is the authority on its own schedule. Do it for five or six flights across a week.
If the destinations match, your tracker's route data is current. If you find reversed legs, or city pairs the airline no longer flies, you are looking at a cached database that has not been refreshed since the last season change.
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Related: how live flight tracking works · flight trackers compared
Quick answers
Does ADS-B include the flight's route? No. An ADS-B broadcast carries position, altitude, speed, heading and the callsign. It does not carry the origin or destination. Any tracker showing you a route has looked it up somewhere else, using the callsign as the key — and that lookup is where routes go wrong.
Why does my flight tracker show the wrong destination? Almost always a stale route database. Airlines republish their schedules twice a year at the IATA season change, flight numbers get reassigned to different city pairs, and a free database that cached the old pairing keeps serving it. The aircraft is being tracked correctly; the route attached to it is out of date.
Why do some trackers show a route backwards? A flight number is usually used for both the outbound and return leg on the same day, distinguished only by the schedule. If a route database stores the pairing without knowing which leg is in the air, roughly half the time it shows the journey in reverse.
When do airline routes change? At the IATA season boundaries. The summer season runs from late March to late October and the winter season from late October to late March. Route data cached across one of those boundaries without being refreshed is the single commonest cause of a wrong destination.
Why do military and air ambulance flights never show a route? Because they genuinely do not have one. A police helicopter or an air ambulance is not flying a scheduled service between two airports, so there is no origin and destination to look up. A tracker that invents one for them is guessing.
How can I check whether my flight tracker's routes are right? Pick an airliner overhead, note the callsign and the route your tracker shows, then look the flight number up on the operating airline's own timetable. The airline is the authority on its own schedule. Doing this for five or six flights across a week tells you quickly whether a tracker's route data is current.