Many flights with no positions on my station.

Why are so many of the flights I’m picking up not showing positions? Is that a hardware issue with the aircraft or my station? I know I’m not in a good place for MLAT but I was under the impression that ADS-B was intended for the aircraft to be able to broadcast their position. Is that not the case? Or will it be by 2020?

Generally, aircraft that you hear but which don’t show a position only have a basic Mode S transponder, not an ADS-B transponder. Those are the ones where you need mlat. In the US, ADS-B transponders seem to still be in the minority.

I’m also showing many more flights without positions as stated in this related post:

From another thread about call missing call signs

I believe those are using mode-s as mentioned, even if mlat is working keep in mind that locally, you’re only seeing your own data, so you won’t see the result of mlat. But that data going to flightware along with other’s in your area most likely contributes to mlat working. At least that’s my guess anyway. I see a lot of those too and it’s typically local flights like Dash-8’s that probably don’t have ADS-B. Sometimes they show some data like altitude and tail number but no position.

This isn’t quite how MLAT works.

The FlightAware MLAT server and sites are in constant communication about what planes are seen by each site and if MLAT is possible. If MLAT is possible for a plane then the server will request more messages for that individual plane and then an MLAT solution is found by the server once it collects all the messages. These MLAT positions are then fed back from the server to the sites.

Basically some things need to happen:

  1. There needs to be a relative timing model for each site calculated.
  2. Sites need to see a mode-S plane and the server need to find matching sites that see the same plane.
  3. Once 4 or more sites see the exact same message a MLAT solution is found
  4. send back the position to each site that helped with the MLAT solution

Any steps that fail will cause MLAT to not work. But in your case it probably is due to a plane being seen by less than 4 sites.

TL;DR : The main thing to know is that MLAT is done on a per plane basis. Seeing a plane locally on your site and having MLAT turned ON means that the FA MLAT server knows your can see the plane. The server just needs more messages for an MLAT solutions to be found.

I see quite a few “dashes” along MLAT paths in my feeder’s web display. Are these the result of one or more of the steps failing. It seems to be a high number of missing MLAT plots. I see this at all altitudes and all over the coverage range of my receiver.