Silvaire wrote:
What can be seen clearly though is that Mode S provided full-time mandatory tracking by tail number, and Mode C doesn’t, and UAT doesn’t.
Well, I guess that if all you have is a hammer then everything looks like a nail.
Silvaire wrote:
The whole rational for mode S was issues with mode A/C which reduced the usability of secondary radar for ATC.I think rationale in this instance means excuse, because there is no evidence this was a real world limitation, one that actually affected ATC operations. What can be seen clearly though is that Mode S provided full-time mandatory tracking by tail number, and Mode C doesn’t, and UAT doesn’t.
@Silvaire, we don’t know how much more expensive the Eurocontrol system would have been if the A/C was not implemented.
In short – ATC wants a MAC address for every aircraft, and Mode-A/C can’t provide it. :)
Well, I guess that if all you have is a hammer then everything looks like a nail.
In this instance I apparently share my lack of naïveté with the US aviation community that successfully defeated mandatory Mode S, and thereby mandatory tracking.
Yes exactly. There is no scientific/engineering evidence that the solution which Mode S offers was actually needed. Exactly the same with 8.33.
Another “it may work in practice but will never work in theory” purist approach, so common in Europe.
And people who don’t want to be tracked just go incognito, and then everybody loses. TCAS stops working, which is a serious safety issue since airliner TCAS uses (for GA detection purposes) only Mode A/C. Airliners use Mode S for TCAS 2 i.e. mutually negotiated resolution advisories.
And we all pay for this, with 4 digit installations. Well, the one positive thing is that Mode S drove a large scale transfer of old junk transponders
into a dumpster. Same with 8.33 
Can anyone spot a pattern here?
Silvaire wrote:
Well, I guess that if all you have is a hammer then everything looks like a nail.In this instance I apparently share my lack of naïveté with the US aviation community that successfully defeated mandatory Mode S, and thereby mandatory tracking.
It is not a question of “naïveté”, but of a budget – US aviation budget is big, and the customer does not pay.
Yes, fairly obviously while tracking was the motivation for implementing Mode S, the main motivation for mandatory tracking is the opportunity it offers to tax without difficulty. If you don’t recognize that, I’d continue to consider it naive.
Peter wrote:
Another “it may work in practice but will never work in theory” purist approach, so common in Europe.
I’ve wrote it above, but it seems I have to do it again. The issues with mode A/C are real and it was the FAA that contracted the development of mode S! I again suggest you read the relevant sections of the Wikipedia article on secondary radar.
OK let me rewrite it 
From wiki:
A number of problems are described in an ICAO publication of 1983
So, yeah, somebody identified a tech issue in 1983 but nowhere does it say that this turned out to be a real problem.
I don’t doubt it was a real theoretical problem
The human universe is full of issues which were identified forty years ago and which haven’t happened.
Silvaire wrote:
Yes, fairly obviously while tracking was the motivation for implementing Mode S, the main motivation for mandatory tracking is the opportunity it offers to tax without difficulty. If you don’t recognize that, I’d continue to consider it naive.
That is not my understanding of the justification for Mode S. It was more capacity based, two way communication, along with increasing the data available. Tracking for the purposes of user fees is a perversion that it may have enabled, but was not the justification. I have attached a hostory of the development of mode S, it is an interesting read. Mode A/C as well as Mode S are used for ATC tracking targets. ADS-B with or without anonymity are used for the same purpose. UAT has an anonymous mode that offers some level of privacy, but allows target tracking. In the US, the FAA has a PIA program that issues N number assignments and their associated Mode S code that are intended to provide some privacy because the N number is found in the FAA registry with no information on what the aircraft true N number is. Pilots using the PIA load the pseudo N number or mode S code into their transponder along with a third party call sign and file flight plans using the third party call sign, like FFL028 for ForeFlight zero two eight to use in telephony.
That is not my understanding of the justification for Mode S. It was more capacity based, two way communication, along with increasing the data available.
I think political motivation, which is what creates law, and technical motivation are two different things that can both exist simultaneously. The political motivation is obvious in this case and in the US it is equally obvious that this would not be discussed by FAA, which does not pass law and is not responsible for providing its own funding.
A long term strategy for a new tax requiring technology change does not get discussed by lawmakers at each step, it gets created piece by piece until all the pieces are in place and a relatively simple change in law creates the tax itself. That process can occur even when the technical motivation is not compelling otherwise.
Neither would AOPA discuss the issue completely openly for fear of alienating their congressional contacts but one can see why UAT includes autonomy, and it wasn’t because FAA had motivation in that regard. It was a negotiated political compromise that resulted in an ADS-B mandate being successful in significant US airspace where a Mode S mandate had never been similarly successful.
