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Getting registration # out of a Mode S return

How can this be done?

There must be at least 2 ways.

One is decoding the 24-but number. I recall reading (in the distant days of Usenet) that there is a simple algorithm for mapping an N-reg reg to the 24-bit number. Other countries e.g. UK use a mapping which needs a database lookup.

Another is that the aircraft reg is configured directly in a transponder such as my GTX330 and is thus probably transmitted. Is it?

I once flew in an N-reg Cessna 400 with the Avidyne kit (described here) and we could see aircraft registrations, but only the N-reg ones. I have since found out that that capability of the Avidyne 60x TCAS kit works only via RS232 (not ARINC429) and thus worked only with the older (Avidyne) displays, not say a G500/G1000 etc.

Administrator
Shoreham EGKA, United Kingdom

Another is that the aircraft reg is configured directly in a transponder such as my GTX330 and is thus probably transmitted. Is it?

Any Mode S Transponder must downlink the Aircraft Identification, which must correspond to item 7 of the flight plan. For GA flights, this is usually the registration, for scheduled flights the flight number.

LSZK, Switzerland

I just lookup the number at airframes.org. Yours is A0375B...

So a Mode S transponder, correctly configured (they aren't always) will transmit the aircraft reg in two different ways: directly, and via the 24 bit code?

Administrator
Shoreham EGKA, United Kingdom

Message format with ES The registration is not in the list of fields, only the aircraft call sign.

EGBE - Coventry, United Kingdom

So a Mode S transponder, correctly configured (they aren't always) will transmit the aircraft reg in two different ways: directly, and via the 24 bit code?

For GA flights, yes.

LSZK, Switzerland

But only in the US, the 24-bit code is derived from the registration. In Europe it is assigned by the CAA. The same functionality could be provided by including a lookup database in your avionics (e.g. airframes.org). I guess this will become available in the new future, in PowerFlarm et al.

Just yesterday, I was looking at ADS-B returns from aircraft around Prague using a $14 USB DVB-T receiver stick and a piece of free software called ADSBscope. All aircraft do indeed report the call sign and altitude, and some (but not all) of the big ones also report coordinates, heading and speed. The only light aircraft with an extended report was N10DK, a PA46.

LKBU (near Prague), Czech Republic

Hmm, surely for situational awareness you would really want to call signs (aka Flight IDs) rather than registrations? These are available from all Mode S transponders in current production, and use a common format, so should be easy to decode everyone's callsign.

This article is a good overview of the different types of data available from Mode S in its different modes. Looks like you would need to send a UF20 (alt) or UF21 (Squawk) interrogation in order to receive the Flight ID from an elementary surveillance transponder.

Final Edit more googling suggests the specs say that that UF20 and UF21 interrogations are only sent by ground stations, not by ACAS stations. No idea why this is...

EGEO

The N-reg to 24-bit mapping seems to have been worked out by a simple inspection of the FAA aircraft reg database and the corresponding 24-bit codes. It was published in Usenet in 2008.

What I find puzzling is why the TCAS in that Cessna 400 was showing only N-reg tail numbers, when G-reg tail numbers have to be emitted on Mode S also.

Presumably Avidyne have implemented the FAA 24 bit to tail number decode, which is simple enough, but have not implemented the database lookup for the rest of the world. And they are not using the tail number which is emitted literally.

Those ADS-B boxes (example) which exist are pretty clever. I am extremely reliably informed that my plane is visible from many miles away, despite being "elementary" mode-s only i.e. radiating only the 24 bit code, the tail number, and I believe a flag indicating whether I am capable of more or less than 150kt. These boxes are connected to the internet and they compare their reception of the extended squitter packets (which are clearly time-stamped by each receiver) and they then use triangulation to position you (same as the sferics sites position the discharges). This is much more than a radar controller will see, unless you have a discreet squawk etc. But no ATCO is allowed to have such a box on his desk...

With an "enhanced" mode-s emitter (anything above 250kt TAS, etc) the plane emits GPS lat/long as well, so positioning becomes trivial. And airliners emit lat/long continuously on ADS-B anyway.

I see that the Kinetic box can also receive ACARS and that can carry lat/long too - as it did usefully with AF447.

Administrator
Shoreham EGKA, United Kingdom
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