FlightAware Discussions

Mlat - sudden dramatic fall in total

Folks, good friend of mine ( ralondon ) has something strange happening on his FA data today, Saturday 21 September. His daily mlat aircraft total is usually around the 400-500 mark but for some reason today it is just four (4). His ‘other’ total has increased substantially by nearly as much as the mlat has fallen.

He tells me his stats page mlat shows as green so assume is operating.

Anyone suggest what may have happened?


Link his stats maybe?

The graph can normally tell you if MLAT was out for any longer period of time.

It’s this one: https://flightaware.com/adsb/stats/user/ralondon

The “other” category consists of received mode-s aircraft that do not transmit a location or have an mlat derived position, so if mlat is not working then any aircraft that were appearing under mlat will appear under other.

It looks as though the range he is getting is about 80nm, which although is not particularly far, should cover a large number of other receivers given the location and be enough for mlat to work - it has been up until now.

Perhaps if he has a look in the log to see if there are any error messages there it would be informative.
To see it, he should log into the pi and type this command:

journalctl -u piaware --no-pager

The mlat-client will show its status there every 15 minutes or so, and might give a clue.

When it’s working normally it should look something like this:

Sep 21 20:19:18 raspberrypi piaware[4105]: mlat-client(4377): Receiver status: connected
Sep 21 20:19:18 raspberrypi piaware[4105]: mlat-client(4377): Server status:   synchronized with 756 nearby receivers
Sep 21 20:19:18 raspberrypi piaware[4105]: mlat-client(4377): Receiver: 2109.7 msg/s received      302.1 msg/s processed (14%)
Sep 21 20:19:18 raspberrypi piaware[4105]: mlat-client(4377): Server:      0.1 kB/s from server    0.1kB/s TCP to server     3.4kB/s UDP to server
Sep 21 20:19:18 raspberrypi piaware[4105]: mlat-client(4377): Results:  49.5 positions/minute
Sep 21 20:19:18 raspberrypi piaware[4105]: mlat-client(4377): Aircraft: 12 of 33 Mode S, 89 of 155 ADS-B used
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I thought you could see anyone’s stats by deleting your own username in the URL and inserting the other username in - I often view your’s as well as my friend’s. Good for comparison re locations.

His stats are as follows;


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It’s clearly not working at all, see the red line vs the orange/yellow line.

Also the status page normally shows:

Multilateration (MLAT): Supported / Enabled (synchronized with 336 nearby receivers)

But with his page, it doesn’t show the synced part, that means it’s not synchronizing.


Thanks for detailed reply - he is not in to forums, keep telling him how friendly this one is but to no avail. I will pass on message and let you know outcome.


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Replace the power supply and see if that helps.

Reception overall has dropped as well, something clearly went bad.

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Not aware of that command, just issued it on my Pi and wow, some list, quite a few days.

Does that recycle or delete after a few days?


It’s kept in RAM on raspbian, so as not to write unnecessarily to the sd card. It does cycle after a few days, though I forget how long it retains logs for.

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Thank you,

I’ll pass that message on to him. Not sure what PSU he is using but know it is just a Zero so doubtful even 500mA would be used.


On the zero there can also be power problems specifically with power delivered to the dongle.

If power supplies go bad, they go bad.
So even if the zero uses little power, with low voltage the dongle won’t work properly.


Ah yes, I see that.

Shall let him know.


That is weird, when he ran this it said ‘No Journal file’.


Strange you mention PSUs going bad, seems I’ve just had a PiHut 1500mA fail - not on a PiAware but another Pi project. Illuminates the power LED but won’t boot, replacement PSU boots fine.

PSUs are deceptive, give the impression they work but sometimes don’t.