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You can't squawk 1200 with a 1090 ES transponder

digidocs

digidocs

Well Known Member
Hey VAF,

Up until recently I had been planning to install a 1090 ES transponder to achieve ADS-B OUT compliance. However, I recently discovered that doing so makes it impossible to be anonymous to ATC.

No matter what you put on the dials, a 1090 ES transponder will always be transmitting a unique 24 bit code that be directly associated with your N-number. It continuously transmits your speed, altitude, GPS position, and N-number--- can you say violate-o-matic?

The 978MHz UAT transmitters incorporate an anonymous mode that eliminates this problem, but I rarely see this issue highlighted. I really hope that we'll see more sub-$2K UAT options (for use with our existing IFR GPS). Garmin are you listening?

UAT is more expensive, requires extra antennas, and is only usable in the US below 18K, but it lets us keep the ability to "squawk 1200" in an increasingly regulated environment.

David
 
When I rob a bank and have to go on the lam for while till the heat drives down, I head for the woods. Flying an airplane never seemed to me to be a good way to lay low, with ATC, flight plans, curious pilots at every airport, etc. :)
 
My understanding is that the anonymous feature on UATs is only good until 2020. After 2020, you can't use that feature.
 
To the best of my knowledge the current rules will allow you to continue using the anonymous mode. Here's an excerpt from the final 2020 rule:

TSO?C154c includes a feature to temporarily and randomly assign a 24-
bit address for UAT-equipped aircraft. This rule does not prohibit the use of
this feature. UAT-equipped aircraft conducting VFR operations that have
not filed a flight plan and are not requesting ATC services may use this feature.

(http://www.gpo.gov/fdsys/pkg/FR-2010-05-28/pdf/2010-12645.pdf)

David
 
digidocs said:
Up until recently I had been planning to install a 1090 ES transponder to achieve ADS-B OUT compliance. However, I recently discovered that doing so makes it impossible to be anonymous to ATC.

No matter what you put on the dials, a 1090 ES transponder will always be transmitting a unique 24 bit code that be directly associated with your N-number. It continuously transmits your speed, altitude, GPS position, and N-number--- can you say violate-o-matic?
Click to expand...

This has been widely known for quite a long time now.

Actually mode-S extended squitter doesn't transmit your N-number at all, but it does transmit your aircraft's unique ICAO address code which can be directly used to look up your N-number in the FAA's registration database.
 
Actually it does transmit your N Number and the ICAO address. We display other planes N Numbers on our EFIS map screen. You can actually calculate the ICAO addres from the N Number, it is not a random number.

Rob Hickman
Advanced Flight Systems.
 
N401RH said:
Actually it does transmit your N Number and the ICAO address. We display other planes N Numbers on our EFIS map screen. You can actually calculate the ICAO addres from the N Number, it is not a random number.

Rob Hickman
Advanced Flight Systems.
Click to expand...

So, if you change your N-number, do you get a new ICAO address? If so, do you have to get your transponder re-programmed somehow? What if you buy a used transponder? Etc. :confused:
 
My transponder manual documents how to configure the ICAO 24 bit aircraft code. It is very straightforward.

In fact, it has always struck me as a rather weak mechanism as anyone with less than legal intentions could easily setup their transponder to pretend to be me!
 
digidocs said:
Hey VAF,


No matter what you put on the dials, a 1090 ES transponder will always be transmitting a unique 24 bit code that be directly associated with your N-number. It continuously transmits your speed, altitude, GPS position, and N-number--- can you say violate-o-matic?


David
Click to expand...

I suspect a more basic motive than just plain old enforcement. The design of this system complete with all your information will enable automatic computer generated user fees. The cost of administration of user fees has been a great deterrent to fees. That argument will be gone in 2020. I hope that doesn't happen, but let's face it - it makes it easy.
 
The FAA does record all flights and at OSH they had the system up where if you gave them your N-number, they would pull up all your flights.

The fear is, if you nick some controlled airspace, or fly VFR when their computers say it is IFR, you name it, they could come after you.

A friend mentioned to the FAA guy who was running the booth at OSH that pilots have the choice of either entering bogus data into their transponders accidently, of course, or just turning the thing off. Who hasn't made a flight and forget to turn their transponder back on? Not that I would EVER suggest any do anything in violation of the regulations, laws, or AIM.
 
Last edited:
N401RH said:
Actually it does transmit your N Number and the ICAO address. We display other planes N Numbers on our EFIS map screen. You can actually calculate the ICAO addres from the N Number, it is not a random number.

Rob Hickman
Advanced Flight Systems.
Click to expand...
Is this only for 1090ES? I was under the impression that, at least with a UAT, that only the 24 bit ICAO code was being transmitted for brevity of transmissions.
 
PCHunt said:
So, if you change your N-number, do you get a new ICAO address? If so, do you have to get your transponder re-programmed somehow? What if you buy a used transponder? Etc. :confused:
Click to expand...

I don't think so.

I don't have a Mode S on the Tiger, but the FAA registration on-line data shows the assigned ICAO number.

I changed the N number during a repaint, but the ICAO number stayed the same. I believe it's assigned to the aircraft, not the registration number.
 
Gil - the ICAO code is mathematically derived from the N number. Whether or not the FAA's registration computer accurately reflects that is a function of the FAA, not of ICAO. The correct answer remains that if you change your registration number (or registration letters in Canada) you should change the ICAO code programmed into your Mode S transponder. Don't forget that if you have a 406MHz ELT you likewise need to change the ICAO code programmed into it.
 
Technically, an ADS-B transmitter transmits both Flight ID and your tail number. However, if you aren't a scheduled flight, you don't really have a flight number, so the requirement is for your registration to be in the Flight ID. For guys with flight ID's, they actually have to enter this in the transponder each flight. ATC really only cares about your Flight ID. Most EFIS systems display the Flight ID because it's what you'll hear a plane called by ATC, so when you see that 767 it's easier to know it's UA768 than N123UA.

Both a UAT and a Mode-S transponder spontaneously emit the flight ID. A Mode-S transponder also has the registration number, independent of the Flight ID, but this is only emitted if it is queried by the ground radar. A UAT alternates between Flight ID and the registration number to save bandwidth.

In the USA, your registration and ICAO code are mathematically related, so if you get the ICAO code, you can figure out the tail number. This is just the way the USA assigns ICAO codes. Other countries do it differently.

A UAT is allowed to randomize the ICAO code, Flight ID, and Registration number when squawking 1200. A Mode-S transponder is not.

--Ian
Dynon Avionics
 
If a pilot had something to hide... it would be almost undetectable, if he simply gave another callsign on the radio.
Worrying about taxes, user fees and such is rather pointless.
Taxes and death. We are all eligible. Tin foil hats are cheap to make and kind of stylish, right?
ADS-B will be a good thing... with more SA for WX and traffic.
 
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