Where it is
Latitude and longitude, measured on the aircraft and broadcast.
The lookup
Where does a flight route come from?
Where does a flight route come from, if the aircraft overhead is not announcing it? From a list. The radio message has a position, a height, a speed, a heading and a callsign. Someone else then looks that callsign up and attaches a pair of airports. That attachment is the part trackers disagree about.
The dot can be right while the destination is last season's. FlightAbove shows a from and to when a route is known, and leaves them off when it is not. How the position itself is heard is a separate step.
What the aircraft actually says
Five things in the message, and one that is not
ADS-B on 1090 MHz is a position report, sent about twice a second. It is enough to put the aircraft on a map. It is not a timetable.
How high
Height, which FlightAbove shows in feet once the report is received.
How fast, which way
Speed and heading. Useful, and still not a destination.
A callsign
The flight name the crew are using, such as BAW286. This is the key the lookup uses.
A tail, sometimes
The registration of that airframe, when the message includes it. Still not a city.
Not the airports
No departure. No arrival. "London to Malaga" was never in the radio message.
After the radio
Three places a city pair can come from
Every product that prints "from" and "to" has chosen one of these, or a mix. They are not equally fresh, and none of them is the aircraft talking.
What that number used to do
A community list of callsign to city pair, built from flights people have already seen. Free, and common. It remembers the pairing, including the one the airline stopped flying.
What the airline planned
The published timetable. Right on the day it was issued. It does not know that this morning's aircraft went technical, or that the flight was retimed onto a different city.
What is actually in the air
A paid feed that checks the plan against the aircraft that took off. Closer to today. It costs money per look, which is why a lot of hobby maps never buy it.
Why the destination is off
Four ordinary ways a lookup goes wrong
The timetable flips twice a year
Around the end of March and the end of October, airlines publish the next season. Numbers move between cities in bulk. A list that cached the summer pairing will keep offering it through the winter.
The same digits, the other way
A morning Manchester to Dublin and the later Dublin to Manchester can share a number. Store one pair, with no sense of which leg is airborne, and the screen points backwards for about half the day. That is the aircraft that looks as if it is arriving from the airport it has just left.
The number is borrowed
One flight number can mean a different city pair on a different day of the week. After a merger, inherited numbers can belong to another part of the network entirely.
Some flights have no pair
Police, air ambulance and a lot of military flying are not a scheduled service between two airports. There is nothing honest to print. A tracker that prints a route anyway has invented it.
To check one yourself, take the callsign off the screen and look that flight up on the airline that is operating it. Do it for a few airliners across a week. Matching cities means the lookup is current. Last season's airport, or the journey backwards, means the list behind the screen has not been refreshed. The number on the ticket and the number in the air are a related muddle, and a different one.
On the desk
A route when it is known
FlightAbove is a display for the aircraft you can hear, out to 250 km. The callsign, the type, a photo of that type, the height in feet and the speed come from the broadcast and the networks that join it up. The from and to are shown when a route is known for that callsign.
When it is not known, the route stays off. An air ambulance does not get a made-up city pair, and a quiet sky stays a clock and the weather. The screen is not a distress service, and it is not trying to be the airline's timetable.
Hardware from £99.00, paid once, produced in the United Kingdom
Shown
Callsign, type, photo, height, speed. A from and to when the lookup has one.
Left blank
No city pair for police, air ambulance, or a callsign the list does not know.
Not invented
No aircraft drawn in to fill a quiet window, and no destination drawn in to fill a gap.
Quick answers
Questions about flight routes
Does ADS-B include the origin and destination?
No. The broadcast carries position, height, speed, heading and a callsign. It does not carry the airport the aircraft left, or the one it is going to. Any from and to on a screen was attached afterwards.
Why does a flight tracker show the wrong destination?
The position is measured. The city pair is a lookup, and lookups go stale. Airlines rewrite their timetables twice a year, and a list that still has last season's pairing will keep serving it.
Why is the route shown backwards?
A short-haul number is often used both ways on the same day. A morning outbound and the later return can share it. A list that stores one pair, with no idea which way the aircraft is pointing, will reverse the journey for half the day.
When do airline routes change?
Twice a year, around the end of March and the end of October. Summer and winter timetables swap, and flight numbers move between city pairs. A cached pairing that is not refreshed across that change is a common reason for a wrong destination.
Why do some aircraft have no route at all?
A police helicopter, an air ambulance or a military transport is not a scheduled service between two airports. There is no city pair to find. A screen that fills one in is guessing.
How can I check whether a route is current?
Note the callsign and the cities on the screen, then look that flight up on the operating airline's own site. The airline is the authority on its timetable. A handful of airliners across a week is enough to see whether the lookup is fresh.
What does FlightAbove show when it has no route?
The aircraft, if it is in range: callsign, type, a photo of the type, height and speed. The from and to appear when a route is known. They are left off when it is not. A quiet sky is a clock and the weather, not an invented destination.
How aircraft tracking works · What are planes overhead? · Flight tracker display
The measured part
Trust the position. Check the cities.
Height, callsign and a route when one is known. Produced in the United Kingdom. Hardware paid once.