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I often see military flights in the sky, which do not appear on FlightRadar24. I do understand that low-flying military airplanes do no necessarily get picked up by these trackers, and that some military aircrafts switch of transponders. However some flight do appear on this ADSB-Tracking website. For example currently you can often see USAF F-16 near the Ukraine with a Tanker in the back on some kind of holding pattern.

What logic or factor governs whether a flight appears on FlightRadar24?

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  • $\begingroup$ Transponder On/Off. Just a little while ago, there were 2x F-16 from 31st FW, Aviano AB, IT displayed. Then just one. What you don't see is the literal dozens of other NATO fighter jets roaming around, supported by those multiple tankers. $\endgroup$
    – WPNSGuy
    Commented Mar 18, 2022 at 20:41
  • $\begingroup$ Related: Do flight tracking websites also track non-commercial and defense aircraft? $\endgroup$
    – user14897
    Commented Mar 18, 2022 at 21:29

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Several key things define whether an aircraft shows on Flight Radar and any other tracking site:

  1. These sites do filter some aircraft and choose not to display them.
  2. A plane may choose to turn off their transponder. Military aircraft in particular are exempt from many civil rules and regulations which would see most aircraft having an active transponder and of course their operational requirements will dictate they often do. That said, ultimately, any plane CAN disable it if they wish.
  3. Flight tracking hardware used to feed these sites doesnt work with older transponders. Old transponders require a spinning RADAR dish to pinpoint a bearing and can not be triangulated using static receivers. While most civil aircraft use newer transponders, again, the military is often exempt.
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    $\begingroup$ Flight tracking hardware does work with older transponders, but there has to be more of it and there not always is. Older transponder must be triggered by a spinning radar, but then if three static receivers independent of the radar receive it, they can triangulate the position by comparing the time of reception. But there has to be three of them and there not always is (while for ADS-B one is enough, because position is broadcast). $\endgroup$
    – Jan Hudec
    Commented Mar 18, 2022 at 22:48
  • $\begingroup$ What about low flying aircrafts? $\endgroup$
    – U_flow
    Commented Mar 18, 2022 at 23:11
  • $\begingroup$ @JanHudec AFAIK, For MLAT to work you need the ability to differentiate targets. MLAT only works with Mode S. In theory, as a one off, you could track a Mode A target if you knew the Transponder Code was unique, but AFAIK all of the tracking solutions rely on Mode S's address space to differentiate $\endgroup$
    – Dan
    Commented Mar 22, 2022 at 17:07
  • $\begingroup$ Although now I'm googling further I can find claims of being able to track Mode A/C via MLAT - I'm still sceptical that the tracking sites do so though $\endgroup$
    – Dan
    Commented Mar 22, 2022 at 17:14

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