On Thursday, November 21, 2019 at 5:55:45 AM UTC-8, b4soaring wrote:
On Wednesday, 20 November 2019 17:12:46 UTC, Darryl Ramm wrote:

Oh dear God I went and read CAA CAP 1391, that UK standard this uAvionix box implements. Now I want to stick a sharpened spoon up my nose and remove any memory of this insanity from my brain.

Yep none of the FAA TSO-C199/TABS TCAS-compatibility features seem to be in that spec. (remember TSO-C199 was largely driven by that Minden midair.... where getting compatibility with TCAS II in the Hawker 800 was a likely requirement). So an airliner with TCAS II... looks like it'll fly right into a GA aircraft fitted with a CAP 1391 device with no TCAS RA. How does the UK CAA expect this to work? That ATC alone will keep traffic separated? In the UK where they mix up jet airliners flying into regional airports? This all seems a bad technology choice to me (spend more money and do TSO-C199/TABS and get TCAS compatibility, allow volume worldwide to lower prices--instead now we have very different fractured standards).

And as intended by DO-260B (1090ES standard) these CAP 1391 devices transmit "1090ES Out" but transmit it as DF=18 (downlink format) messages (not that standard DF=17 messages) intended to be used by devices which are not Mode-S transponders... DF=17 is used in the USA by ADS-R and TIS-B messages (those ground towers doing the ADS-R and TIS-B transmitting are not transponders). Now I'm curious if PowerFLARM in the UK will see those DF-18 targets from these devices...

You are mistaken. The vast majority of UK jet traffic is in Class D or A, most VFR GA is in Class G. Any GA in Class D will almost certainly be transponder equipped.


Ah damn I was almost finished up with the spoon thing.

I am mistaken about what? The UK does have airliners flying in class G airspace. It's hopefully infrequent but it happens. There has certainly been concern about that in the past in the UK aviation community. And you have Class G airspace abutting Class D airspace. What happens when an airliner accidentally wanders into Class G or a GA aircraft wanders into Class D? (yes SIL=1 visibility to ATC is a help, if there is ATC ADS-B coverage there, incompatibility with TCAS is just scary).

Few airliners are likely to have 1090ES In (if you have the right gear look at which are broadcasting 1090ES In capability code, it appears depressingly low in the USA). The skyEcho won't show up at all on a pure (non-1090ES In equipped) TCAS, TCAS certainly won't issue a TA against the skyEcho even if it has 1090ES In. The great benefit of TCAS is it's a last resort collision avoidance tool when all else goes wrong, and this CAP 1391 approach removes that last link. Unfortunately uAvionix marketing says that the skyVector is compatible with TCAS. It's not. I've asked them to remove that claim, and hopefully they will soon.

And whats the highest risk type of mid-air in UK class G? It's not GA with an airliner, but that is a high-consequence, low-probability scenario and near busy airliner traffic sure seems worth worrying about. And I'll add in fast business jets (hopefully TCAS equipped, but many still wont' have 1090ES In.. and won't see these devices) and military traffic... (both tactical with IFF or non-tactical (potentially with TCAS)) is unlikely to see these systems--but hopefully folks can check compatibility if near busy military traffic areas.

In an effort to reduce price these systems end up with significant limitations. It's one thing if the users understand those limitations, it's another if they don't, and especially if the vendor is not correctly stating them.

[I expect you understand the limitations but I'll state some here for folks playing along at home]

We've already seen confusion in this thread about the FLARM support in the skyVector. It's FLARM In only, hopefully that's well understood by folks operating skyVecor near FLARM equipped gliders and visa versa. And can those gliders if equipped with a FARM compatible device with ADS-B In see the skyEcho? I would check that actually works.

And if the GA aircraft have a transponder even without 1090ES Out you have to disable the 1090ES Out part of a skyVector... so then other skyVectors don't see it at all (and PowerFLARM with ADS-B option would only see the target via PCAS).

All a somewhat strange beast, with limitations that I hope users understand.. The potential for confusion with the dual-link system in the USA was likely worse than this, so the UK probably does not win the "most stupid" prize here. The European approach to end of life of Mode-S and sticking with 1090ES sure seemed a better/simpler long term approach to me. But now the UK has throw out some of that clean elegant interoperability and complicated things with CAP 1391. And unfortunately it looks like the EU will not mandate a conspicuity device standard so there will be lots of them in existence across the EU. Sigh, the great thing about standards is there is enough of them for everybody to have their own.

It's great that this device includes FLARM In, FLARM bidirectional would have been better, but OK yes raised prices. And one great thing the UK does with SIL=1 sources like this that the USA does not, at least currently, is display that traffic for ATC (if you are within NATS ADS-B In coverage--I've lost track of where that deployment is at)

The lack of TABS/TSO-C199 like transponder interoperability in CAP 1391 comes from building down to a low price. Now with the direction looking like there will be multiple standards worldwide reduces the ability to drive down costs by standardization and improved competition. I really wish there had been standardization around something more like TSO-C199, maybe that was just impossible with the FAA trying to get the TSO spec done fast under pressure... not enough time for international involvement. Who knows.

CAP 1391 is designed to encourage cheap ADS-B in & out (with SIL 1) for VFR GA in Class G. Most glider pilots use Flarm. SkyEcho is popular with power pilots as a GPS & traffic awareness source for navigation software.

Popular? Do you have sales numbers info for these units? Know how many are just used for their GPS and ADS-B In capabilities? (my guess is it might be a lot as they are a nice receiver for folks with GA aircraft, many of which may have transponders already).

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Anyhow since r.a.s. is largely a USA focused forum, the bottom line answer to the question originally asked is these devices are very unlikely to appear in the USA.