The real concern with mode s in the USA giving away the aircraft ID is that third parties who wish to charge for use of their airspace can use the ID or claim that a particular aircraft set off the noise monitors, etc. . The privacy issue is also important for tracking movements for financial gain, for example a business is looking to acquire a company, they don't want it known that their corporate aircraft just landed at an airport where a for sale company is based. Celebrities don't want their movements tracked and so on.
There isn't a mandate for mode S transponders in US airspace by private operators until 2020 when a mode S transponder will be required above 18,000 MSL for ADSB. Below 18,000, a UAT ADSB unit may be used and it can be anonymous as long as you are not receiving ATC services and you don't have a mode S transponder installed. The UAT supports something call anonymous mode where it makes up a random ID when the aircraft is VFR and not receiving ATC services (for example squawking 1200). It doesn't support the feature when a mode S transponder is installed because the mode S transponder must use its 24 bit ID in all cases and if the UAT doesn't use the same ID, the ATC would see the aircraft as two targets with different ID's.
In US airspace below 10,000 feet and outside of class B and C airspace, a transponder is not required. That is most of the airspace below 10,000 MSL. However, more than 90% of aircraft have a transponder.
We set up our Trig Mode S entering code and registration. It would be just as easy to land at a strip, and change both (e.g. to Peter's?) before a low level illegal flight. Then back again to our lawful data. (I miss the smileys on this forum)
And if you know the aircraft tail number can't you just see it on flightaware? Or does flight aware use mode s?
I think the Federal Government point is a very US one. Personally I don't get why it is such big deal.
I have no national ID card and no registered address. If I want to disappear I might quite legally get in my airplane, fly to another state without telling state number one I'm leaving or filing a flight plan, and then I'm gone :-) Having arrived I can quite legally tell no one. Harder to tax people who can do that.
The US system of government is based on the idea of national government as a necessary evil. Making it logistically difficult for national government to track and control people was therefore a fundamental goal.
Like I said, an odd US thing.
As is $6.00/gallon avgas, no 20% VAT, no state sales tax on labor, and no EASA-style aviation regulation. There's a reason for that, and reigning in the Feds is it.
NCYankee, thanks for the additional info on UAT implementation - its very interesting and I'll be happy not to broadcast my N-number when the time comes. BTW, you do need a Mode C transponder outside of Class B or C but within a Mode C veil, assuming the aircraft has an engine driven electrical system. I have one of each.
The 'real' reason stated by FAA for no Mode S probably wouldn't have included include their admitting that massive lawsuits against them were sure to have followed. The biggest potential recipient from tracking aircraft is them. You can bet that the point was clearly made to them.
Not sure they are related.... Shall we start listing almost no gun crime?
I fail to see how federal tracking of aviation relates to the price of avgas.
I would bet a pound to a penny that nearly all of the aircraft flying only with mode A actually have a transponder which is mode C capable, and are only missing an altitude encoder. In some cases it may be impossible to fit an encoder, but it's about the cheapest bit of avionics kit both to buy and fit; some people are just stingy.
I'd say it's more likely to be faulty than missing altogether, or possibly the transponder inadvertently switched to mode A. When flying over Germany, I heard on at least two occasions the ATC requesting some other aircraft to check the transponder because they weren't getting an altitude readout on the radar.
I installed a Mode S (it was 'mandated' at the time) when refitting my a/c and have yet to see any benefit over mode C. No real concerns over privacy, but major concerns over what seem to be random and ill thought out CAA directives. I've not even been able to test it in the air - where in the UK is a ground station can both see a mode s return and talk to me over VHF about it?
A very interesting and valid angle on privacy from NCYankee.
Presumably, the more aggressive journalists are already using the boxes mentioned to track well known people.
Presumably the way to get around that is to fly in a plane which is not connected to you (Netjets will do me fine 
) But it does put a damper on the use of corporate aircraft in sensitive situations.
AFAIK the reg identification works only with Mode S targets. There is no way to identify a Mode C target because it doesn't emit anything useful apart from the pressure altitude. But, in the EU, everything above (from memory) 250kt TAS, or some other things, has to carry Enhanced Mode S, which means radiating loads of extra parameters every time you are pinged by radar. No need for ADS-B to give the stuff away.....
Conversely, aircraft below those thresholds are required to NOT have Enhanced Mode S (they have to use Elementary Mode S) which prohibits radiating the extra parameters. This is of course a stupid Eurocontrol invention because the people who make transponders are mostly American and they have never heard of this, so a GTX330 will radiate everything connected to it, and usually GPS lat/long will be included so de facto (in a radar-rich environment) the result is the same as ADS-B. I recall Garmin later did a "specially for the EU" software fix which enabled e.g. the use of GPS ground speed to switch it AIR/GND without it radiating the "prohibited" GS value, but any plane from outside the EU will be radiating the lot because that's the logical way to wire it all up... One UK avionics shop went public saying they have to rewire hundreds of Mode S installations because of that ruling, but I suppose they will just do a firmware upgrade now. But, anyway, even if a Mode S target doesn't radiate lat/long, it is trackable because every return from it carries the ID (and probably the reg also) so there is no need to track it continuously.
change both (e.g. to Peter's?) before a low level illegal flight. Then back again to our lawful data. (I miss the smileys on this forum)
Just type in those characters as shown.
have yet to see any benefit over mode C.
There is no benefit to GA, over Mode C, and probably never will be.
In the USA, the "carrot" was the upload of traffic data over the Mode S data channel. In Europe, this could have been done also but the ATC providers decided to not spend money on supporting it.
