FlightAware Discussions

Some planes have 2 entries in the airplane list

Latest SkyAware and tar1090.
Have for some time seen a few specific planes (MLAT) to have two entries in the airplane list. One is with the correct call sign (and RSSI) and another with a tilde and then hexid (and a low RSSI). They are also displayed on the map as two planes (not always following each other).
The specific planes can be close to me or far away, makes no difference.
I have just checked and adjust (lowered) my gain, but same issue.
I have read the text information tar1090 display for the tilde version.
My ModeSMixer2 does only show the plane instance with the callsign.
Anyone that can explain why this happens?
br Lars

Unclear from your description whether you’re seeing mlat positions for the “right” entry or not, so there are two possibilities:

  1. One entry is direct Mode S data + mlat results. The other entry is a TIS-B trackfile position.

  2. One entry is direct Mode S data and TIS-B position (using the correct ICAO address, not a trackfile address). The other entry is an anonymized mlat result for a blocked aircraft.

For case 2, if you prefer to disable mlat results for blocked aircraft entirely, you can set piaware-config mlat-results-anon no.

Thanks.
btw. It’s fairly old planes, only seen transmitting mode-s (not adsb).
I see two positions on the map. Sometimes on top of each other and sometime miles in between.
Makes sense, as I believe these few planes sometimes are shown as BLOCKED on FR.
But TIS-B, isn’t that only for ADSB equipment and only in the US (I’m on the other side of the globe with no such services (as far as I know))?
But anyway, just wondered whether I had some issues with my receiver, and it seems not to be the case then :slight_smile:

To receive TIS-B you need ADS-B in. But the positions that are transmitted can include anything that the ground station knows about, including e.g. Mode S or Mode A/C targets (or even primary radar, surface multilateration, etc). It provides traffic awareness of non-ADS-B targets. (For ADS-B targets, ADS-B in will hear those directly)

And yes - it’s US only. So if you’re not in the US then it’s probably the second case. I’m not sure offhand where the positions for the “main” aircraft would be from in that case.