Local SkyAware distances not matching

I’ve got a curious (to me) situation. I have bought another ADSB blue stick as part of my continued experimentation, and I built a second 1/4 spider - placed on the roof near the first.

Looking at my local SkyAware read outs ( and

they are showing different distances to the same planes (?!). It’s a few miles or so - up to ten - but I don’t see why there should be any difference at all. Further, some planes do match for their distance.

How is this distance being computed? I checked on my FA-users stat’s page, and each of the Sites has an identical Lat/Long indicated

But how does my Pi know where it is? I don’t recall giving it a Lat/Long when I set it up (maybe I did and forgot?), so I was presuming it was taking it from my FA page - although now that I think about it, that seems a potentially problematic approach.

Anyhow - have other people with multiple sites seen similar behavior? Does anyone know “what’s wrong” with one (or both) of my installations?

This will be because the last reports received from the planes was at a different time and hence position. If you look at the age figure you can see on the planes with different distances also have a different age. The distance is calculated to to where the plane was at the time of the report. If one of your receivers misses a report then it is calculating the distance to a different position from the other.

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@LawrenceHill In the case of SWA2092, this could be the issue - one report is “aged” 35 [seconds?] and the difference in location is about 6 nm; traveling 6 nm in 35 seconds = 617kts, which seems a bit fast, but at least that’s in the right ball park.

But take HAL71 as an example - they each report “0” for the age - so each has seen a report very recently, yet they are showing the plane’s location as over 10 nm apart(!). At cruising speed it would take an airliner well over a minute to travel 10 miles.

There are a number of other planes that have similar/identical aging values with vastly different locations, some much closer in [PAT287; each at age = 6, distances = 105.9nm, 88nm (!! I hadn’t noticed that large of a difference) ]

I guess this raises a more detailed question in my mind:
How is the distance computed at all? Does the plane squawk its Lat/Long in the ADSB message, and then my local Pi computes a distance (using its own Lat/Long - obtained from ??) or is it more complicated?

position age != age.

Not sure if the skyaware interface shows that. (maybe consider tar1090 if it doesn’t)
Also you need to make sure to restart dump1090-fa after you set the location on the FA stats page.

@wiedehopf looking at the column options it seems that “age” = Message age

So I guess I’m getting messages, but not a position.
I’ll look at tar1090 (seems like you write that, right?) It look like it’s a replacement for my local skyaware page (or can it replace flightaware/skyaware too?) right?

It’s just an extra interface …
Anyhow it doesn’t have a column for it either.
You’ll have to click the aircraft and it’s in the details.
Suppose i could add it.

You could enable lat / lon columns and see if it’s the same.
If it’s not, the distance is for another position.

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great idea - I’ll check that.

I generally use the distance for sorting - a quick way to check what’s the max distance I’m seeing instantaneously instead of looking retrospectively at graph1090, so it’s a “nice to have” for me - but certainly not a reason not to try/switch to tar1090

I’m saying it doesn’t have a “Seen Pos.” column which shows how old the current position is.
Anyhow … i’m tinkering with something else and will probably add that column because the current model for that table doesn’t incur performance penalties for adding more columns if the columns aren’t used.

Ah, thanks for the clarification. Will aim to give this a try tonight.

Keep in mind that this kind of calculation is moot unless the aircraft is flying either directly toward you or directly away from you. An aircraft making a gentle turn at the extreme edge of your range (say, 200nm) could appear to have the same distance from your receiver for several minutes or even more, despite flying at 500+ mph.

A plane crossing your area directly east to west, for example, would appear to get closer up to a point, then the distance would stabilize for a period of time before appearing to get farther away.

From that standpoint, the concept of “distance from receiver” is very close to useless, and the speed of the aircraft doesn’t directly correlate to the change in distance - at least not without some advanced math.

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@wiedehopf - I’ve loaded tar1090 and definitely like the look of the interface over skyaware.

A question on documentation - is there anything that explains what the various features do? The Readme.md at Github was focused on installation (so it seemed) more than operation. For example, if I hover over [P] it says “Persistance mode” - but I’m not sure what that means exactly. It looks like it leaves some planes on the screen after they are “gone” - but how long, and is there any control over that?

Also with [M]ulitview - I can “ctrl-pick” multiple planes, but it only shows me the data from the most recently picked - is that expected behavior?

One thing I like about FR24 that bugs me about FA is in FR24 I can zoom via rolling the middle mouse button/wheel from anywhere on the screen - in FA I need to click on the (-) (+) picks to change the zoom level. Any chance this is functionality that could be added to tar1090, or is that a limitation of how FA data is generated?

Thanks for sharing this great tool with the community!

You can scroll to zoom in skyaware as well as tar1090.
Not sure what you’re talking about.

yes that’s expected.
it’s mostly to compare tracks, also they move to the top in the list.


@wiedehopf for me neither SkyAware or Tar1090 respond to a mouse scroll wheel. FR24 does - as does this forum (moves the thread up and down) … Ah - it’s Firefox that’s the culprit - Edge works fine. Odd, since the wheel does work in Firefox for FR24 and the forum here - it’s not that Firefox can’t read the wheel, but for some reason won’t use it on sky/tar.

Well that’s a nice find - thanks!

Disable firefox smooth zoom or something …

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I found auto-scrolling and smooth-scrolling settings. When i started, both were toggled on. I tried each off, and both off together - none of the combinations made a difference;FR24 (and google maps) zoom on scroll, FA (main site), SkyAware, and tar1090 don’t. (I closed and reopened FF each time) There seems like there ought to be a setting there somewhere - good suggestion - I’ll keep looking.

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