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I use Plane Finder app & noticed they have a “history” area where I can search airspace at a certain place and time.

If I SEE a plane flying, but later check their timeline (on the app), it shows they weren’t flying.

  • What does that mean?
  • Is that possible?
  • Can it mean something was taking place illegally?
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    $\begingroup$ Can you give examples of planes that flew and did not show up on commercial tracking sites? $\endgroup$
    – 300D7309EF17
    Commented Sep 26, 2023 at 18:52
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    $\begingroup$ "Can it mean something was takin place illegally?" No, that's not what that means. $\endgroup$
    – Ralph J ♦
    Commented Sep 26, 2023 at 20:44
  • $\begingroup$ In theory, it's not impossible for this to be an illegal flight? The odds of this are very low considering how many legitimate reasons exist for an aircraft to be flying and not show up on tracking sites... plus as a criminal, hypothetically, why would you do this? $\endgroup$
    – user45266
    Commented Sep 27, 2023 at 20:44
  • $\begingroup$ As you may recall from MH370, flying without a transponder, with an inactive transponder, or outside radio range, leaves no track on tracking sites. $\endgroup$
    – mins
    Commented Sep 28, 2023 at 18:20

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The FAA tracks all IFR flights -- those filed to follow instrument flight rules.

The FAA also tracks VFR flights whose pilots request flight following. This is optional, but commonly done by VFR pilots who are traveling cross country (longer range A to B flights, not short range flights in and out of the same airport).

The FAA does not keep track of aircraft on the ground. If you have an old photo of an airplane with a tail number, and you want to find the airplane, the FAA can't tell you where it is.

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    $\begingroup$ Well, the FAA does also track VFR traffic that isn't using flight following if they're within a area covered by radar, they just don't control that traffic. They still track it in order to prevent conflicts with traffic that they are controlling. And the FAA also typically tracks and controls traffic on the ground if it's on a taxiway or runway at a towered airport. They don't typically track aircraft on the ramp or on the ground at untowered fields, though. $\endgroup$
    – reirab
    Commented Sep 27, 2023 at 16:26
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    $\begingroup$ I agree that VFR non-flight-following traffic appears on radar. However, does the FAA associate an N-Number with it? I.e. do they identify which aircraft it is? Perhaps it was just my interpretation, but I took the question to mean "are they following me?...." not "do they know what is in the sky". $\endgroup$
    – Rob McDonald
    Commented Sep 27, 2023 at 23:49
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Not sure which app exactly you are using, but most flight tracking sites and apps use ADS-B and MLAT to determine a plane’s position (and more).

Both require the aircraft to be equipped with a suitable transponder.

A lot of GA aircraft are not equipped with one and are thus completely invisible on such sites. Even some airliners may or may not be equipped (depends where). Military aircraft may be equipped or not, and may turn it on or off depending on the mission, or even during different parts of the mission. Other specific aircraft (like emergency services, firefighting aircraft…) also may or may not be equipped.

So a plane could very well be in the air and not show up on those apps and sites.

On the other hand, in some airports you may be able to see some ground vehicles which will never get off the ground shown on the maps, because they are equipped.

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    $\begingroup$ Plus, some aircraft (military, government) may be equipped and with the transponder turned on, but some sites (esp. FR24) intentionally hiding the flight from display. (And the flight being visible on other tracking sites, or by using your own ADS-B receiver.) $\endgroup$
    – Mormegil
    Commented Sep 27, 2023 at 8:07
  • $\begingroup$ @Mormegil Ah, I didn't know about that. Is that documented or do you know of specific cases? $\endgroup$
    – jcaron
    Commented Sep 27, 2023 at 8:11
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    $\begingroup$ Sure, it’s not secret, FR24 explains it e.g. at flightradar24.com/how-it-works#blocking $\endgroup$
    – Mormegil
    Commented Sep 27, 2023 at 8:20
  • $\begingroup$ @Mormegil And that also applies to private aircraft that have requested for their aircraft to not show up on those sites (FR24/FlightAware.) (Though that 'other' site still shows them.) $\endgroup$
    – reirab
    Commented Sep 27, 2023 at 16:13

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