Silvaire wrote:
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.
Pray, tell: how do you do this? I’m not aware of any Class B that doesn’t have the Mode C 30 Nm veil. Curious…..
Peter wrote:
That is an ATC-butt-clenching assumption if you see a Mode A target flying here, and merging with an airliner
You need mode S with altitude for the two locations on Stansted approach path as it is a TMZ
a 24-bit integer which is the “hex ID”, and the aircraft reg
It ends up being the a/c registration for most light GA. But the real name is Flight ID and needs to match what is in your flight plan and your callsign.
So you can’t cross validate ICAO address (hex id) and flight id
ATC can’t normally see the Mode S pressure altitude (they can see only the Mode C pressure altitude)
It will of course depends for each ATC unit. But the whole point of mode S is to be able to selectively interrogate specific transponders. So you interrogate more often a/c going fast or changing level. So I wouldn’t think they just bin the data.
(what is, I believe, true is that some of the additional information are not necessarly presented or easy to access depending the ATS unit)
Silvaire wrote:
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.
172driver wrote:
Pray, tell: how do you do this? I’m not aware of any Class B that doesn’t have the Mode C 30 Nm veil. Curious….
We’ve covered this before. In the US, aircraft with no engine driven electrical system can and do operate in Mode C veils, including any Class D airspace areas, without any transponder. They cannot operate without prior permission within Class C or B airspace, or overfly Class C or B airspace. 14 CFR 91.215
Peter wrote:
In a Mode S box you separately configure two things: a 24-bit integer which is the “hex ID”, and the aircraft reg.Actually, you configure the 24 bit ID and the call sign. Of course for private ops the call sign will essentially always be the same as the aircraft reg, but there are flight schools that fly even SEPs with company call signs.
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.
The point of switching off ALT is to prevent an erroneous altitude from being transmitted. The altitude info in mode S is also disabled. (E.g. for the Trig TT31, the manual states that “altitude information is suppressed”.)
Silvaire wrote:
That way if radar shows the aircraft, it’s known to be under the floor of the Class B not above it.
Around the class B areas in the US is a 30 NM area that requires mode C from the surface. Also New York class B tops out at 7000 MSL.
Note: replied in sequence to reading. Although aircraft originally certified without an electrical system may operate inside the 30 NM Mode C area and below the B, they will only show as primary targets to radar, so won’t be mode A or C or … and won’t show on TAS, TCAS, or ADS-B.
NCYankee wrote:
Around the class B areas in the US is a 30 NM area that requires mode C from the surface.
Again, quoting 91.215:
(3) Notwithstanding paragraph (b)(2) of this section, any aircraft which was not originally certificated with an engine-driven electrical system or which has not subsequently been certified with such a system installed, balloon or glider may conduct operations in the airspace within 30 nautical miles of an airport listed in appendix D, section 1 of this part provided such operations are conducted -
(i) Outside any Class A, Class B, or Class C airspace area; and
(ii) Below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport or 10,000 feet MSL, whichever is lower
NCYankee wrote:
Although aircraft originally certified without an electrical system may operate inside the 30 NM Mode C area and below the B, they will only show as primary targets to radar, so won’t be mode A or C or … and won’t show on TAS, TCAS, or ADS-B.
Obviously true. In my area, Class D ATC within a Mode C Veil is very helpful in terms of identifying the aircraft using primary radar (they seem to enjoy it) and if talking to them it is useful to provide altitude info that I wouldn’t normally say when flying my Mode C equipped aircraft.
It all comes down to clear understanding of rules and reasonable, cooperative behavior. ATC’s job is to convey traffic within the rules, not to make them up and FAA controllers are IME very careful to appear cooperative and inclusive. Occasionally you run into a trainee FAA controller who doesn’t understand the rules (they are often ex-military), which is understandable given the small number of aircraft without an engine driven electrical system, but in that case I’ve found the word “waivered” works without a lot of back-and-forth.
Silvaire wrote:
We’ve covered this before. In the US, aircraft with no engine driven electrical system can and do operate in Mode C veils, including any Class D airspace areas, without any transponder. They cannot operate without prior permission within Class C or B airspace, or overfly Class C or B airspace. 14 CFR 91.215
Interesting, learned something again today! I suspect there aren’t many like this in the L.A. area, I certainly never had a traffic call that would indicate that ATC had the target on primary radar only.
A self-sustaining reservoir of electrons does have certain advantages for aircraft operation, so there aren’t many aircraft without one 
Mainly its antiques, often those with 65 HP engines and that’s a very small group. Since there aren’t a lot of them and since pilots flying that kind of plane typically have greater than average competence, it all seems to work out without excluding anybody. If there is ever a collision between a non-electrical aircraft and an airliner within a Mode C veil, you can bet the rules will change, but I think the chances of that are slim to none.
Returning to Mode S on Flight Tracking sites, the only time I appeared was when within range of Glasgow Radar, squawking 7000 and talking to nobody. Weird track as I was flying around peaks, and it frequently lost the signal. Class G, below 4000’.
A co-owner is a site volunteer, based SW of Inverness at that time.
