SonexBuilders.net

So, Jeff and I are out flying in our respective Sonex in a tight formation and my ADS-B receiver finally lights up to show traffic on my WingX app on my iPad. Jeff shows up 150 ft ahead and at the same altitude. It also shows another target a couple miles away. But something I've never seen before, Jeffs registration number comes up on his icon. And the registration number comes up on the other target. It looked just like what ATC might see an IFR clearance.

I thought our transponders were anonymous and the FAA couldn't track us by number. How did ADS-B tie Jeffs transponder signal to his registration?

Must be a mode S transponder.

The Mode S transmits the ICAO address, unique to each aircraft

http://en.wikipedia.org/wiki/Aviation_t ... tion_modes

142YX wrote:Must be a mode S transponder.

The Mode S transmits the ICAO address, unique to each aircraft

http://en.wikipedia.org/wiki/Aviation_t ... tion_modes

Correct, it's not the ADS-B logic, it's the mode S.
(At least in here in Australia) When you register your aircraft you get assigned a "flight id", a code which you need to program into your mode S transponder.
When a Mode S transponder gets interrogated it will respond with not only the squawk code (like the old mode A/C transponders) but also include this flight id in the reply. ATC can then tie that back to your aircraft registration regardless of what squawk code you've dialed in.
It is interesting your WingX app is able to find the corresponding registration for a given flight id as well, it must have access to a database containing the flight id / registration link.
Does anybody know if this information is published somewhere?

Yep, the database is available right here:
http://www.faa.gov/licenses_certificate ... _download/

It's small enough that I wouldn't be surprised if most devices contain the entire database.

Ryan Turner reverse engineered an algorithm that relates N numbers to ICAO address (worked for every address in the FAA registry in 2013):
http://www.pilotsofamerica.com/forum/sh ... stcount=61

I haven't been able to find an official public domain algorithm.