FlightAware Discussions

Advantages on using "--forward-mlat" in dump1090?

I am feeding a local Virtual Radar Server coming from my two RPi devices.
The MLAT aircraft are not shown in the list, but listed in the table of aircraft.

Now i’ve seen that dump1090-fa has a command line opion “–forward-mlat” which is not used in the default installation.

The description says “Allow forwarding of received mlat results to output ports”
Are there any benefits enabling this option on the RPi devices?


Avoid using it. Combine the mlat results separately in VRS.

Not on the map is what you mean to say?
Just add MLAT as a separate receiver/input in VRS. (FA MLAT is by default offered on 30105, you can also get MLAT results from some other mlat networks, maybe try 30157)
Mark it as MLAT.

Correct, made a typo. The aircraft are not shown on the map.

I’ve read about yours and @obj suggestion regarding two receivers, but whenever i tried this after a while the VRS stopped with an exception error

But i will give it a try again. Maybe the problem is somewhere different.
Both should be operate in AVR or Beast Mode and on port 30005 rsp. 30105(MLAT).
Is this correct? I did not change the defaults for dump1090-fa so far


I’ve set it up and at least the last 10 Minutes it’s working.
Forget about the names of my two devices. I am not very creative :slight_smile:

I’ve had the same issue and some of my own MLAT aircraft never actually showed on the map at Essex Radar although they were in the list. I’ve marked the two feeds as MLAT in the merged feed so let’s see if that makes any difference.

VRS will otherwise information from the feed it saw the aircraft on first, which will be without position.

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I’ve now set up two feeds per receiver. One is on 30005, the other on 30105
However the flag for MLAT is sometimes shown for aircraft which are reported via port 30005.

Like this example. The receiver shown is the “R3” which is bound to the 30005, otherwise it would be documented from “R3M” which is my internal name for the MLAT port 30105 of one of my devices.

Maybe VRS interprets the MLAT incorrect or did not change the flag after it was taken over from the MLAT port.
At the end it doesn’t matter, all aircraft are registered and shown on the map

Well both receivers are providing data for the aircraft aren’t they?
And you’ll always get ModeS data before you get an MLAT position.

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Yes, thanks for the explanation.