FlightAware Discussions

What happened to MLAT on PiAware?

I guess I missed a memo. But MLAT hasn’t been contributing to positions on my PiAware station for a couple of months now. And when I checked, MLAT isn’t contributing for a number of neighboring stations. So I don’t think it’s just a problem with my gear.

Did I miss a release note?

How can PiAware be sync’d with 217 other receivers and not report any MLAT-derived positions?

It’s just a graph scaling artifact, they’re not really zero. The number of ADS-B positions are swamping the number of MLAT positions. Click on the ADS-B items. That will disable them, you’ll see a line through them, and the graph will auto-rescale for the remaining MLAT entries.


You can see the MLAT positions on my graph top out around 600, which on my first graph won’t even come up half way to the first grid line of 2000.

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In the USA, it’s not uncommon now to see zero MLAT aircraft at any given time thanks to the ADS-B mandate. This is quite a change from a few years ago.


Thanks for the suggestion and the comment, folks.

It would be clearer to say that:
(a) MLAT positions used to be a larger fraction of the total number,
(b) MLAT positions used to outnumber “Other” positions,
© the total number of daily reported positions seems lower than formerly (by ~15%).

Perhaps it’s just the time of year and there’s usually less traffic during winter in my area. It’s the first winter for my station; its first “anniversary” is a week off.

I’ve seen a big downturn in the last 18 months of MLAT traffic - with a peak in the summer and a steady decline after that. The range of the graph is 10/18 - Current. This covers ~35 nodes primarily in the NE, SW, Central & Great Lakes regions. stats pulled from the MLAT Avg traffic of my FA team page.


This is consistent with what we see overall - globally the number of mlat results we generate has dropped by about 50-60% over the last 12 months. (I don’t have unique aircraft counts easily available, unfortunately, but I’d expect those to show something similar)


My UK/Japan/Canada nodes have also seen an already sparse amount of traffic go to nearly zero

That’s good news in the USA as the FAA deadline for ADS-B Out implementation was 1/2/2020. Most active aircraft have upgraded.

There are still non-compliant aircraft buzzing around, or so a local tower controller told me yesterday. ATC informs them “Your ADS-B seems inoperative.” Eventually those operators are going to get calls from the FSDO.

So yes, MLAT counts in the USA should decline towards zero in 2020.

Not quite.

Plenty of GA aircraft use 978 device (tailbeacon for example) that isn’t programmed but derives its hex id from the Mode S transponder that is already installed.

Those will still be MLAT when they aren’t in range of a UAT station.
And even if they are being received via 978, MLAT may still be performed if they are using some of the private code shenanigans for UAT.
Not sure how the number counting will work, but they will likely always be counted twice in the foreseeable future.


Right. Eric’s comment reminded me of a friend in Washington state who got to wrestle with adding an ADS-B transponder to his old aerobat last year. He’s legal now.

Tailbeacon literature says it can be used with a Mode A/C transponder. The aircraft’s Mode S ICAO hex code is programmed into the Tailbeacon for transmittal only on 978.