FlightAware Discussions

TIS-B Targets contain unknown ICAO and no Registration N number

I’m getting lots of targets (source TIS-B) which contain no valid identification. A screenshot shows one aircraft highlighted with what appears to be a hex ICAO ID code prefixed by tilde ‘~’ as follows: ~2A0A0E. This is not a valid US ICAO aircraft registration number. Notice in the screenshot that every aircraft using this symbol decodes the same way.

Photo can be viewed here:
Google Photos

Why is this and how can it be resolved?

The ~ signifies TIS-B data.
Those are not received directly from the aircraft, which needs to be clear.

Also i believe the TIS-B data does not contain the hex-id of the aircraft being shown.

The ~ prefix means this is a non-ICAO address.

In this particular case this TIS-B data will be radar track data; the address is a trackfile identifier, not an ICAO address.

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So TIS-B comes from the ground station - an airborne receiver is supposed to use it to display potential traffic conflicts. Without an ID (either ICAO or Registration) how does the airborne receiver correlate the TIS-B with other targets it sees? I’m confused. Here is a typical TIS-B that I’m capturing:

*952a0666993c0190200660854c43;

CRC: 000000

RSSI: -5.9 dBFS

Score: 1400

Time: 1292084.83us

DF:18 AA:2A0666 CF:5 ME:993C0190200660

Extended Squitter (Non-Transponder) Airborne velocity over ground, subsonic (19/1)

Other Address: 2A0666 (TIS-B, other addressing scheme)

Geom - baro: 2375 ft

Ground track 180.0

Groundspeed: 128.0 kt

Geom rate: 0 ft/min

NACv: 7

It doesn’t seem to have any way to correlate with a known target. What am I missing? Is this the equivalent of a primary only target?? During a 30 second dump I saw three distinct targets (based on “Other Address” value.)

Any insight would be appreciated.

Thanks

Yes, something like that. It’s a radar track with the ground infrastructure doing the correlation; it might be a primary-only or A/C target. The airborne receiver isn’t expected to correlate it with anything else, it’s just a traffic notification.

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Does anyone have a copy of the relevant TIS-B specs I could look at? Seems they are locked behind a gov’t sponsored paywall called the RTCA and available at HUGE prices, like four digits.

Welcome to the wonderful world of expensive aerospace specifications :frowning:

There’s no spec I know of that describes how the data underlying TIS-B is generated; it’s just whatever the FAA does. Presumably some of it will be piggybacking off the back of ASDE-X / ASSC etc.

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