I work with an engineer whose answers seem to contradict each other, but upon careful examination, he found the questions to be different, deserving different answers.
I can’t decide if he is inconsistent 
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I live in the wilderness, both in terms of piaware north of me, and the number of aircraft.
Looking last night, Skyview showed 0 for a while.
Looking at hourly received reports shows some hours with 6 reported.
My “positions reported by this receiver” showed a couple of interesting hits.
One was 80 miles, out to sea, northwest of me. The fact that I reported at 80 miles, the first to see a flight coming in from the Pacific suggests that there are no piaware, or any other reporters, in that direction.
Another was only 40 miles, but in a northerly direction. The other reporters are airports that are a long ways away. Can I tell if those other reporters are actually airports, or piaware stations with the airport listed merely being their “closest” and not actually the airport?
For instance, the flight UAL294
Sun 08:54:33 AM 38.9382 -122.9604 is my report that was used.
How did you establish no other station received that flight or you were the first to receive that flight?
Also have a look at the coverage map, the coverage seems fairly good up to 200 nmi out on the pacific. (30000ft - 40000ft)
I decided I was “first” because the listing in ANA8 prior to my entry was
Oakland Oceanic and then 
FlightAware Approximate, followed by my entry at Sun 08:06:30 AM 39.0166 -123.8018, and then a steady list of reports from various sources. Looking at the tracklog now, my entry is not the first. Either some backfill has occurred, or I was mistaken earlier.
So why do MLAT aircraft disappear from Skyview for a period of time? 5 minutes or more!
Obj provided this response
Almost the more receivers in your area, the worse your MLAT will be - or did I not understand?
I have been looking more at the “Flights with Positions From This Feeder”, as I ponder where coverage gaps are, around me.
One by one, I pick the lat/long from a position that I provided, and look at where they are.
I presume that my position is only used when no one else is available, or that there is some ranking involved, if several report the same position.
They are in places that I wouldn’t expect. Not great coverage for me, but maybe impossible for other sites.
I also see an odd selection of reporting airports in sequence in the list.
Oakland, mine, San Jose, Chico, Napa… this doesn’t seem to follow the flight path.
I intend to copy them all to a “my positions” file, and make a little map.
Maybe a picture will tell the story.
That assumption is not valid in my experience. The sky at 30000 ft and above is very very very well covered in my area.
Still i have “Flights with Positions From This Feeder” at that altitude.
If multiple stations have good coverage of a flight it is probably randomly attributed to one station after checking the data against the other reports.
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My receiver is sycronized 160 receivers. If this theory is right, I would barely see any MLAT flights.
But I see plenty.
So no, I don’t buy that theory. Once you subscribe to MLAT you get the results no matter how they are calculated.
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I’m currently synced with 181 receivers, with about 49 MLAT flights onscreen, aircraft ranging from 16 to 215 nm away. But only a small handful of those planes are below 10,000 ft level, perhaps 4 of them, so more receivers are picking up the high alt aircraft.
Stray thought: I wonder if user altitudes affects MLAT fixes , depending on where the other synced receivers are located ? (eg 4 ADSB receivers within 40 miles, 3 of them at 1000 ft elevation, the 4th ADSB receiver at 5000 ft elevation) Might be possible to be synced in that data is being received and sent to FA, but to have the fix data discarded upon calculation of the combined data as it doesn’t pass error checks ?
MLAT is a 3D calculation anyway. Receiver height needs to be entered correctly.
You won’t get synced anyway if the height is set wrong.
Whatever i’m not quite sure how the MLAT results work. The grace time of 3 minutes could mean you get most MLAT results even if you only participate calculating 1 position every 3 minutes.
It’s a mystery 
83 MLAT aircraft yesterday, out of 585. 2,000/22,000 positions.
I’m surprised at how much my MLAT synced number varies.
I’ve seen 181, 85, and right now, 206.
Refreshed, a minute later, 17 synced. two minutes later 260.
Is that number based on the number of aircraft with current hits from MLAT partners?
My case points to differ.
2200 ADS-B, 850 MLAT, 155 Other.
All while I am sync with 195 other receivers.
Would be bloody great if from all those stations, I am selected in so many cases.
Nope, if one look at my neighbors, they all have similar ratios. Mathematically would not make sense what you are proposing.
The grace period is just that… If you are sending MLAT signals to FA, you are given that. You stop sending those, they stop sending back after 3 minutes.
There is no clause of “if we are choosing your data” in there.
Do you think you only get to see an MLAT flight while you are providing hits on that aircraft? (Plus a three minute grace after.)
What about showing an MLAT aircraft while you are synced with any MLAT site that sees that aircraft? That would result in early appearance, and late disappearance, relying on your MLAT neighbors.
I suspect but can’t prove that I only see an MLAT flight for which I am receiving Mode-S signals whether they are used by Flightaware or not.
If I am not receiving a signal from a plane I wont see it in Skyview. Note that in Skyview there is an RSSI for every plane displayed.
When I was in a more remote location it was apparent that some of the MLAT sites I was synced to were about 100NM away. If I received MLAT aircraft merely because I was synced to them I would be seeing MLAT aircraft 100NM past him and that was clearly not the case.
I speculate that to see an MLAT plane in Skyview as a minimum you need to receive a Mode-S packet that matches the mode-S packet that has been received by at least 4 other receivers that you are synched with you. Then and only then does FA send back an MLAT position to you regardless of your packet being used in the calculation.
As with everything else with Skyview, you have to hear it for it to be displayed and therefore antenna height and view are paramount. If you don’t hear it you don’t see it in Skyview.
Again, this is merely speculation.
S.
Mmmh, due to this discussion I have been looking at individal mlat tracks, and several times I still received messages at least every second from an aircraft, but I did not receive any position data. ie the track had gaps.
Some tracks where odd, relatively close I “lost” the plane, and then 50+ miles further away it reappeared. Maybe depend on the overall mlat coverage, currently I am connected to 450 nearby receivers, which is a lot, almost half of all receivers in Germany or eg almost all receivers in the Netherlands.
This rather points to the idea that only if your data is used for mlat, then you receive position messages?
Not possible. If there are 450 sites with only 4 providing MLAT, statistically your signal would be used 1 in 100 flights. You would see that ratio in your flight results.
Or, if you think that you’reso lucky that only your flights are selected, you can take a look at your neighbors. They would have no MLAT flights.
The real life results are nowhere close to that. So I think that as long as your data reaches FA servers in timely matter, plus 3 min grace, we get back MLAT results.
Calculations are complicated enough without keeping track of who’s samples are actually used. That would be a huge overhead.
So, why didn’t get any position info, even though I received messages from the aircraft?
Well, some receivers are better located than others, and generally receive more planes and further away, so they are more likely to be used for mlat. There are not normally distributed.
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I agree with you and have stated my reasoning earlier
But i will not restate my argument or argue that each position calculated the used stations could change. I will also not argue that the computing overhead is not any more extended than that which needs to be done for MLAT anyway.
Arguing is pointless sometimes.
Also MLAT screenshots from my colocated receivers:
Oh no i started arguing again -.-
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The tl;dr is:
If your receiver provided a copy of a message that was used to produce a multilaterated position for an aircraft then:
a) that one position will count in your site stats as a mlat position;
b) your piaware will receive all multilaterated positions for that aircraft for the next 3 minutes
For your receiver to be used, there are a lot of factors in play (e.g. happening to hear the right message, having synchronization with other receivers hearing the same message, rate limiting in the solver, local receiver density, etc), many of which are out of your control, which is why step (b) exists - so long as you manage to get one contribution every 3 minutes, you’ll get a continuous track.
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Finally, we got schooled 