I’m a little familiar with adsbexchange as I use it quite often, less with FR24, flightaware and others.
There is no “switch” to swich off visibility on FR24 but still radiate ADSB or Mode ACS. Anything you radiate can and will be picked up.
Most of these sites can and will receive both ADSB and Mode A/C/S. They depend however on a network of “volunteers” that have ADBS receivers at home.
Most networks will filter out “sensitive” aircraft : e.g. military aircraft are never shown. (although they are tracked). adsbexchange does not filter, but has a more limited network of volunteers. (i believe adsbexchange started essentially as a guy on his attic with some friends with receivers. I find it remarkable what he has accomplished.)
I have such a “ADSB” receiver at home (although it is not connected to any network). I can see any ADSB / Mode A/C/S close by.
Jujupilote wrote:
Our 172s (8 of them) where all equipped in 2017 and none of them still appear in the FR24 database.
The flight ID is filled with the registration AFAI can tell from the screen.
I’m puzzled …
Try squawking something else than 7000 and climb and let us know the results.
@Peter: side question: what is your TCAS solution?
Peter wrote:
On a Mode S transponder you can switch off Mode C (i.e. the altitude readout) but you cannot switch off the Mode S
I wasn’t aware of that, thanks for mentioning it. I checked the panel now, and indeed only has “ON” and “Altitude” setting. Althought in the technology the mode S is an add on to the A/C signal, apparently it is not supposed to be switched off.
ATC appears to care most about Mode “C” (altitude) → on a recent event with couple of hundred pilots, someone from ATC was presenting and was really asking everybody to switch on mode C . The reason is: if you fly in class G but below a control zone, without mode C ATC can see you, but can not see what altitude you fly, and they have to route commercial traffic around you, even if you fly at 1000 ft, and the airliners are at 10.000 ft. So you are not busting any zone, but still disrupting traffic.
Well my aircraft has no inbuilt GPS but then neither do my friends which appear on these sites.ATC are clearly seeing me and my details as per ModeS which has been checked so TCAS equipped aircraft will see me.The installation which included a new digital encoder was initially over reading by 200ft in flight on standard pressure altitude which was annoying as I spend a lot of time under altitude constrained airspace <1500 ft.It was checking satisfactorily on ground test.Engineers tracked it to leaky static feed to encoder which meant it was reading cabin static in flight rather than P1 altimeter static source hence the error.I have noticed similar errors In lots of the aircraft I fly which makes me wonder if a significant proportion of the minor vertical infringements triggering CAIT may not be infringements at all.My previous setup under read by an in tolerance 200 feet which seemed a much happier state of affairs !
sugarcube wrote:
ATC appears to care most about Mode “C” (altitude) → on a recent event with couple of hundred pilots, someone from ATC was presenting and was really asking everybody to switch on mode C . The reason is: if you fly in class G but below a control zone, without mode C ATC can see you, but can not see what altitude you fly, and they have to route commercial traffic around you, even if you fly at 1000 ft, and the airliners are at 10.000 ft. So you are not busting any zone, but still disrupting traffic.
Which is why non Mode-C aircraft (including non-transponder aircraft) in the US are limited to 10,000 ft, which is also the altitude to which terminal area Class B airspace typically extends. That way if radar shows the aircraft, it’s known to be under the floor of the Class B not above it.
The flight ID is filled with the registration AFAI can tell from the screen.
In a Mode S box you separately configure two things: a 24-bit integer which is the “hex ID”, and the aircraft reg. They have a direct relationship but the box doesn’t check that. For N-regs (and possibly others – see here and here) the relationship is algorithmic, for others it is a database lookup. So you could configure only one of these, or configure both and have them not matching, etc, and perhaps FR24 is checking this? If I was running a site, even a free one, I would take care to not present bogus data, so it would be logical for FR24 to be checking the consistency. I am fairly sure ATC uses just the aircraft reg, and doesn’t check the 24-bit ID for consistency; this was definitely true some years ago.
what is your TCAS solution?
This. Best ~12k I ever spent… until the full TKS. You do need a competent installer, however.
and indeed only has “ON” and “Altitude” setting
I am not sure about this, and we have past threads on it, but IIRC the Mode S data includes the Mode C pressure altitude, and it may include it even if you have switched off “Alt”. ATC can’t normally see the Mode S pressure altitude (they can see only the Mode C pressure altitude) but FR24 probably uses the Mode S value because it’s easier.
Well my aircraft has no inbuilt GPS but then neither do my friends which appear on these sites
GPS is not relevant to any of this, unless you are using a Mode S transponder to transmit ADS-B OUT (which very few people do, in GA).
I have noticed similar errors In lots of the aircraft I fly which makes me wonder if a significant proportion of the minor vertical infringements triggering CAIT may not be infringements at all
They are supposed to give you a 200ft margin, AFAIK. Then, AIUI, somebody makes a decision on whether to prosecute, and if not then they ask you to do the online tutorial route, etc.
That way if radar shows the aircraft, it’s known to be under the floor of the Class B not above it
That is an ATC-butt-clenching assumption if you see a Mode A target flying here, and merging with an airliner 
Most aircraft in/under US terminal areas are Mode C equipped anyway, so it’s not a big deal. But it so happens that I fly a bit in a plane that isn’t, around and under Class B, so I think about the issue.
Europe seems to be unduly focused (some might say obsessed 
) with GA traffic interfering with CAT passenger planes, with even the most remote possibilities and tiniest ‘cracks in the armour’ causing ‘butt-clenching” concern. I don’t know exactly why, but lack of ATC experience with GA must be a factor. People know where the airliners are likely to be in Class E airspace.
Outside of Mode C Veils, airliners descend as a regular practice though Class E airspace, below 18,000 feet, potentially (and in my area actually) filled with hang gliders and everything else. Since pilots, even hang glider pilots , don’t want to fly in higher risk zones where they might get an aluminum enema it doesn’t seem to be a practical problem.
“They are supposed to give you a 200ft margin, AFAIK. Then, AIUI, somebody makes a decision on whether to prosecute, and if not then they ask you to do the online tutorial route, etc.”
Peter a friend of mine who is a controller at Gatwick tells me that the 200ft txpdr tolerance is ONLY given to aircraft on a verified squawk.If you are on a conspicuity or 7000 squawk and your altitude read out puts you vertically in controlled airspace even by only 100ft which could easily mean you are actually legitimately entitled to be where you are the CAA/NATS process is initiated without mercy.There is now no flexibility on this.After 22000 infringement free hours I am very keen to ensure my txpdr does not falsely accuse me.NATS are target driven and not interested in the facts.At present I do not know anyone who has managed to pass the online tutorial and I know a lot of instructors and examiners who have had to take it.
sugarcube wrote:
The reason is: if you fly in class G but below a control zone, without mode C ATC can see you, but can not see what altitude you fly, and they have to route commercial traffic around you, even if you fly at 1000 ft, and the airliners are at 10.000 ft. So you are not busting any zone, but still disrupting traffic.
I think something is lost in translation or any TMA and airways with more than sporadic traffic would grind to an halt.
Just think the amount of traffic under the London TMA without transponders or ModeA only and the amount of traffic getting into Heathrow/Gatwick/Luton …
The UK way is that primary and mode A only a/c are deemed below (or above) the controlled airspace.
