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Flightradar 24 / FR24 - how exactly does it work?

They would probably use METAR data, and interpolate it (probably by fitting a polynomial to it, like one can do for the magnetic variation) to create a pressure surface. But they aren’t doing any of that.

Administrator
Shoreham EGKA, United Kingdom

I may have spotted something interesting re FR24.

7000 Mode S squawks don’t show up reliably, and often appear to be missing totally. This has always been known.

Looking at my 2 flights today, both show up in their entirety (well, when high enough). However, both had 7000 sections. But both started non-7000.

Hence I think FR24 tracks 7000s ok only if the track starts as non-7000.

There may also be an altitude component thrown into the algorithm.

Administrator
Shoreham EGKA, United Kingdom

FWIW @Peter, your flights last week all seem to show up on Flightaware, presumably they were cylinder break in and VFR? However, nothing is showing on October 29th. Source of data is listed as this

Last Edited by Silvaire at 29 Oct 18:50

Yes; I am plain old Mode S (year 2005 GTX330) so position had to be MLAT. I am not radiating position.

Last week were all VFR local flights, up and down the coast. Today I went to LFAT.

I can’t recall the details but sometimes one departs from Shoreham with a local tower squawk, say something like 3762. After that I might be on 7000. However, a “local” flight can be entirely on 3762 even if I go 50-80nm away and don’t tell them I am changing enroute.

It is certainly clear that just setting 7000 doesn’t terminate tracking.

Administrator
Shoreham EGKA, United Kingdom

My experience is that altitude is used for filtering. When doing local flights in the Extra, I need to get higher than about 3000 ft for FR24 to notice. For larger airfields, all traffic is displayed regardless of altitude. Another thing could be line of sight to nearest receiver.

Last Edited by loco at 29 Oct 19:51
LPFR, Poland

Peter wrote:

Hence I think FR24 tracks 7000s ok only if the track starts as non-7000.

Tracks me as 7000 just fine. It probably depends more on antenna sites and whether multilateration is working for you, and your observations of 7000 being missing are merely a coincidence with FR24 not being able to multilaterate you for that flight.

FR24 also gets things wrong, it said I flew to Kemble once when the track quite clearly shows me all the way to the surface (including taxi) at Gloucester!

Andreas IOM

Having just done a flight which proves the opposite of what I posted above, I agree

It started on 7000, changed to 7xxx for a local ILS, then back to 7000, and tracking shows the lot (apart from lost tracking due to too low).

Administrator
Shoreham EGKA, United Kingdom

My home field is behind a 5-600ft ridge.
On the S-mode planes, we are not visible on FR24 until ~1500ft AGL where we apparently get good enough LOS to enough receivers for MLAT.
One plane has ADS-B out, ie radiating position, and is visible on FR24 taxiing on the apron.
Squawk code is irrelevant, as long as the XPDR is sending something so the server can calculate the TDOA. from all the MLAT ground-stations in range.

ESMK, Sweden

FR24 is now showing drones, and perhaps more interestingly some big drones have Mode S

Administrator
Shoreham EGKA, United Kingdom

That is not a typical drone, it is 200kg and has own G-reg with more avionics than a new Cirrus SR22

Paris/Essex, France/UK, United Kingdom
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