Does FLARM meet TABS requirement?

[Mark Palmer]

Hey all,

I'm in the process of writing my response to the FAA's ANPRM on transponders in gliders. One of the items covered in the document is TABS (Traffic Awareness Beacon System) under TSO-C199. Does FLARM come under this TSO?

I hadn't heard of TABS before reading the ANPRM, and while it talks of low cost avoidance systems it doesn't give any examples.

Thanks.

Mark Palmer
Greenwood Village, CO

[Steve Leonard[_2_]]

On Monday, August 3, 2015 at 10:50:41 AM UTC-5, Mark Palmer wrote:
> Hey all,
>
> I'm in the process of writing my response to the FAA's ANPRM on transponders in gliders. One of the items covered in the document is TABS (Traffic Awareness Beacon System) under TSO-C199. Does FLARM come under this TSO?
>
> I hadn't heard of TABS before reading the ANPRM, and while it talks of low cost avoidance systems it doesn't give any examples.
>
> Thanks.
>
> Mark Palmer
> Greenwood Village, CO

Hi Mark,
Unfortunately, no. FLARM would not be an approved TABS device. And I hadn't heard anything of TABS before this ANPRM, either.
Steve Leonard

[Mark Palmer]

Thanks, Steve. That's what I thought but wanted to be sure.

Mark

[Mark Palmer]

Out of curiosity, is there any equipment currently on the market that meets the TABS requirement?

Mark

[Steve Leonard[_2_]]

On Monday, August 3, 2015 at 11:06:16 AM UTC-5, Mark Palmer wrote:
> Out of curiosity, is there any equipment currently on the market that meets the TABS requirement?
>
> Mark

Nothing that I am aware of. Requirements were just finalized in October of last year. I would need to dig back through some discussions I have have with others, but think of TABS as pretty much a Mode S transponder with the GPS input for "extended squitter" or 1090ES out. There are some other differences, but that is probably the closest description you will find of "TABS in 100 words or less".

Steve

[Darryl Ramm]

On Monday, August 3, 2015 at 11:00:01 AM UTC-7, Steve Leonard wrote:
> On Monday, August 3, 2015 at 11:06:16 AM UTC-5, Mark Palmer wrote:
> > Out of curiosity, is there any equipment currently on the market that meets the TABS requirement?
> >
> > Mark
>
> Nothing that I am aware of. Requirements were just finalized in October of last year. I would need to dig back through some discussions I have have with others, but think of TABS as pretty much a Mode S transponder with the GPS input for "extended squitter" or 1090ES out. There are some other differences, but that is probably the closest description you will find of "TABS in 100 words or less".
>
> Steve

There are two parts of the TABS specification, Class A devices which is a slightly stripped down Mode-S transponder with 1090ES Out and Class B devices which are a GPS Source to provide the input to Class A TABS devices. Full Mode S/1090ES Out transponders can also meet the requirement of TABS devices, and so opens up the possibility of using a TABS Class B GPS to drive those for TABS use.... but for example that (currently at least) will not be usable to meet any of the 2020 ADS-B Out carriage mandate for (powered aircraft). And since TABS only exists as a TSO for devices, there are TABS installation, carriage or use regulations *at all*... so anything beyond what the boxes technical specs are is totally unclear, and what the SSA should be workign on, what ends up happening with TABS could be useful or could be horrifically bad for gliding and other aviation segments.

I expect/hope that being able to eventually meet FAA 2020 ADS-B Out carriage mandates for GA aircraft using (hopefully) lower-cost TABS Class B GPS sources is something that AOPA and EAA really want to see happen.

There seems to be widespread confusion about TABS Class B GPS sources, while technical aspects of the TSO was written to make it possible to use some consumer GPS chipsets, that GPS product still needs to be manufactured by a TABS TSO holder, and has to meet specific complex tests (using a constellation simulator as described in the TSO spec). And in order to actually ship a "TSO'ed product" that manufacturer has to be licensed and working within the the regulated avionics manufacturing process in their country/regulatory area. So at least based on interpreting the current TSO, and understanding some of the concerns the FAA has about GPS technology, folks won't be connecting any old consumer GPS source to a TABS box or a Mode S Transponder.

PowerFLARM does not transmit 1090ES Out (it does receive 1090ES In) so is not a candidate to be a TABS Class A device (but again it will "see" aircraft equipped with TABS Class A devices, which is great). And neither is it a TABS Class B device... it's easy to tell, it does not have a TSO-C199 sticker on the box :-) Doing the work to produce a TSO-C199 compatible version of PowerFLARM is something FLARM would have to talk to, but as things currently sit it is not a suitable GPS source for a TABS Class A device.

NexNav have announced their Micro-i TABS Class B GPS source. I have no idea on pricing or availability. I suspect it is likely that Nexnav may only want to pursue the embedded/OEM market for products like this. Given the complexity of dealing with a TSO like the TABS TSO, it is quite possible that only existing GPS Avionics manufactures would produce TABS GPS sources... even if they actually use COTS GPS chipsets, so sorry to be a downer on all those "consumer GPS" hopes.

Trig Avionics (who make *great* products) is using their TT-20 TABS device in trials in the UK, I don't think there is public information available on the TT-20 or any info on possible commercial availability of the TT-20. But clearly it is likely just a feature stripped TT-21. I suspect the TT-20 has an integral (OEMed) GPS source, if so then as a combined box would be both a Class A and B device.

[Darryl Ramm]

On Monday, August 3, 2015 at 12:39:51 PM UTC-7, Darryl Ramm wrote:
> On Monday, August 3, 2015 at 11:00:01 AM UTC-7, Steve Leonard wrote:
> > On Monday, August 3, 2015 at 11:06:16 AM UTC-5, Mark Palmer wrote:
> > > Out of curiosity, is there any equipment currently on the market that meets the TABS requirement?
> > >
> > > Mark
> >
> > Nothing that I am aware of. Requirements were just finalized in October of last year. I would need to dig back through some discussions I have have with others, but think of TABS as pretty much a Mode S transponder with the GPS input for "extended squitter" or 1090ES out. There are some other differences, but that is probably the closest description you will find of "TABS in 100 words or less".
> >
> > Steve
>
> There are two parts of the TABS specification, Class A devices which is a slightly stripped down Mode-S transponder with 1090ES Out and Class B devices which are a GPS Source to provide the input to Class A TABS devices. Full Mode S/1090ES Out transponders can also meet the requirement of TABS devices, and so opens up the possibility of using a TABS Class B GPS to drive those for TABS use.... but for example that (currently at least) will not be usable to meet any of the 2020 ADS-B Out carriage mandate for (powered aircraft). And since TABS only exists as a TSO for devices, there are TABS installation, carriage or use regulations *at all*... so anything beyond what the boxes technical specs are is totally unclear, and what the SSA should be workign on, what ends up happening with TABS could be useful or could be horrifically bad for gliding and other aviation segments.
>
> I expect/hope that being able to eventually meet FAA 2020 ADS-B Out carriage mandates for GA aircraft using (hopefully) lower-cost TABS Class B GPS sources is something that AOPA and EAA really want to see happen.
>
> There seems to be widespread confusion about TABS Class B GPS sources, while technical aspects of the TSO was written to make it possible to use some consumer GPS chipsets, that GPS product still needs to be manufactured by a TABS TSO holder, and has to meet specific complex tests (using a constellation simulator as described in the TSO spec). And in order to actually ship a "TSO'ed product" that manufacturer has to be licensed and working within the the regulated avionics manufacturing process in their country/regulatory area. So at least based on interpreting the current TSO, and understanding some of the concerns the FAA has about GPS technology, folks won't be connecting any old consumer GPS source to a TABS box or a Mode S Transponder.

[Darryl Ramm]

On Monday, August 3, 2015 at 12:47:32 PM UTC-7, Darryl Ramm wrote:
> On Monday, August 3, 2015 at 12:39:51 PM UTC-7, Darryl Ramm wrote:
> > On Monday, August 3, 2015 at 11:00:01 AM UTC-7, Steve Leonard wrote:
> > > On Monday, August 3, 2015 at 11:06:16 AM UTC-5, Mark Palmer wrote:
> > > > Out of curiosity, is there any equipment currently on the market that meets the TABS requirement?
> > > >
> > > > Mark
> > >
> > > Nothing that I am aware of. Requirements were just finalized in October of last year. I would need to dig back through some discussions I have have with others, but think of TABS as pretty much a Mode S transponder with the GPS input for "extended squitter" or 1090ES out. There are some other differences, but that is probably the closest description you will find of "TABS in 100 words or less".
> > >
> > > Steve
> >
> > There are two parts of the TABS specification, Class A devices which is a slightly stripped down Mode-S transponder with 1090ES Out and Class B devices which are a GPS Source to provide the input to Class A TABS devices. Full Mode S/1090ES Out transponders can also meet the requirement of TABS devices, and so opens up the possibility of using a TABS Class B GPS to drive those for TABS use.... but for example that (currently at least) will not be usable to meet any of the 2020 ADS-B Out carriage mandate for (powered aircraft). And since TABS only exists as a TSO for devices, there are TABS installation, carriage or use regulations *at all*... so anything beyond what the boxes technical specs are is totally unclear, and what the SSA should be workign on, what ends up happening with TABS could be useful or could be horrifically bad for gliding and other aviation segments.
> >
> > I expect/hope that being able to eventually meet FAA 2020 ADS-B Out carriage mandates for GA aircraft using (hopefully) lower-cost TABS Class B GPS sources is something that AOPA and EAA really want to see happen.
> >
> > There seems to be widespread confusion about TABS Class B GPS sources, while technical aspects of the TSO was written to make it possible to use some consumer GPS chipsets, that GPS product still needs to be manufactured by a TABS TSO holder, and has to meet specific complex tests (using a constellation simulator as described in the TSO spec). And in order to actually ship a "TSO'ed product" that manufacturer has to be licensed and working within the the regulated avionics manufacturing process in their country/regulatory area. So at least based on interpreting the current TSO, and understanding some of the concerns the FAA has about GPS technology, folks won't be connecting any old consumer GPS source to a TABS box or a Mode S Transponder.
> >
> > PowerFLARM does not transmit 1090ES Out (it does receive 1090ES In) so is not a candidate to be a TABS Class A device (but again it will "see" aircraft equipped with TABS Class A devices, which is great). And neither is it a TABS Class B device... it's easy to tell, it does not have a TSO-C199 sticker on the box :-) Doing the work to produce a TSO-C199 compatible version of PowerFLARM is something FLARM would have to talk to, but as things currently sit it is not a suitable GPS source for a TABS Class A device.
> >
> > NexNav have announced their Micro-i TABS Class B GPS source. I have no idea on pricing or availability. I suspect it is likely that Nexnav may only want to pursue the embedded/OEM market for products like this. Given the complexity of dealing with a TSO like the TABS TSO, it is quite possible that only existing GPS Avionics manufactures would produce TABS GPS sources.... even if they actually use COTS GPS chipsets, so sorry to be a downer on all those "consumer GPS" hopes.
> >
> > Trig Avionics (who make *great* products) is using their TT-20 TABS device in trials in the UK, I don't think there is public information available on the TT-20 or any info on possible commercial availability of the TT-20.. But clearly it is likely just a feature stripped TT-21. I suspect the TT-20 has an integral (OEMed) GPS source, if so then as a combined box would be both a Class A and B device.
>
> Sigh, I meant to say ..."there are currently *NO* TABS installation, carriage or use regulations *at all*..."

And I'll also add that if things work as usual then and FAA TABS carriage/installation regulations will likely be written with "meets performance requirements of... blah blah TSO". Which would at least allow say folks with experimental aircraft to instal a TABS GPS source that meets the requirement of the TSO even if its manufacture is not formally TSO approved... however, again to be a downer, that does *not* mean folks will be connecting random consumer GPS sources. I expect the best that would happen there is that that TABS Class B GPS device manufacturers, and maybe others, will produce even lower cost "non-TSO" TABS GPS sources.

[Dave Nadler]

On Monday, August 3, 2015 at 3:53:38 PM UTC-4, Darryl Ramm wrote:
> ... I expect the best that would happen there is that
> TABS Class B GPS device manufacturers, and maybe others,
> will produce even lower cost "non-TSO" TABS GPS sources.

For example, probably:
http://newsroom.garmin.com/press-release/aviation/garmin-team-x-introduces-three-new-products-and-adds-new-capabilities

.... The GPS 20A, GA 35 WAAS antenna and install kit is available for $1,225*
.... anticipated to become available Q3 2015.
.... For additional information, visit: www.garmin.com/experimental.

[Darryl Ramm]

On Monday, August 3, 2015 at 2:42:30 PM UTC-7, Dave Nadler wrote:
> On Monday, August 3, 2015 at 3:53:38 PM UTC-4, Darryl Ramm wrote:
> > ... I expect the best that would happen there is that
> > TABS Class B GPS device manufacturers, and maybe others,
> > will produce even lower cost "non-TSO" TABS GPS sources.
>
> For example, probably:
> http://newsroom.garmin.com/press-release/aviation/garmin-team-x-introduces-three-new-products-and-adds-new-capabilities
>
> ... The GPS 20A, GA 35 WAAS antenna and install kit is available for $1,225*
> ... anticipated to become available Q3 2015.
> ... For additional information, visit: www.garmin.com/experimental.

And that Garmin GPS 20A box is already meeting more than the TABS requirement... but because it meets the FAA ADS-B Out mandate requirement it should also be usable with TABS Class A devices. Exact device compatibility would need to be checked and is somethign potentially that TABS installation/use regulations may address (as regulations did by requiring only specific installs of confirmed compatible (via an earlier STC process) of ADS-B Out and GPS devices). Ultimately I expect if TABS takes off pure TABS boxes will mostly end up being integrated Class A and B devices... with some standard Mode S/1090ES out transponders used for TABS compatibility maybe with TABS specific GPS sources.

I think what strategically happens for TABS, for better or worse, is in the hands of large potential drone operators and manufacturers and their lobbyists.

[[email protected]]

On Monday, August 3, 2015 at 3:22:37 PM UTC-7, Darryl Ramm wrote:
> I think what strategically happens for TABS, for better or worse,
> is in the hands of large potential drone operators and manufacturers
> and their lobbyists.

So should be lobbying for a TABS solution for gliders, and at the same time push for being able to use it in class A airspace?

Sure would be nice to be able to get up to cloudbase in the Great Basin area. I'm guessing there's very little traffic near the bottom of this airspace out in this neck of the woods. And ATC could learn how to deal with us since we're pretty much stationary compared everyone else.

5Z

[Darryl Ramm]

On Monday, August 3, 2015 at 7:27:16 PM UTC-7, wrote:
> On Monday, August 3, 2015 at 3:22:37 PM UTC-7, Darryl Ramm wrote:
> > I think what strategically happens for TABS, for better or worse,
> > is in the hands of large potential drone operators and manufacturers
> > and their lobbyists.
>
> So should be lobbying for a TABS solution for gliders, and at the same time push for being able to use it in class A airspace?
>
> Sure would be nice to be able to get up to cloudbase in the Great Basin area. I'm guessing there's very little traffic near the bottom of this airspace out in this neck of the woods. And ATC could learn how to deal with us since we're pretty much stationary compared everyone else.
>
> 5Z

I think any lobbying should carefully lay out what would make TABS suitable for the glider community. And I would include Class A use of TABS in that.....and lots of things about easy installation regulations and more, work with EAA and AOPA on use of TABS Class B devices in towplanes (and all GA aircraft) say near Class C/B airspace instead of full 1090ES Out. But I would expect Class A stuff to apply to block IFR clearance for those Sierra Wave big dogs and use in wave windows where necessary, as transponders are today.. Hoping for a radical change to Class A use is probably a bit much.

[Mark Palmer]

Darryl,

Thanks for the information. That was a lot to think about. I submitted my response to the FAA online just a bit ago. Only 123 responses so far. Several were pro transponder - tended to come from airline and 121 operators.

Mark

[Andrew Ainslie]

https://buy.garmin.com/en-US/US/in-the-air/sport-aviation/gps-20a/prod525504.html

$900 is almost affordable to make my trig tt22 adsb compliant under the new experimental rules. Interesting to see if anyone comes out with anything even cheaper.

[Bob Gibbons[_2_]]

Just curious, what would be the advantage of this unit over using the
1090ES out capability of the GPS source in a PowerFlarm?

Both non-TSO'd, $790 for a PowerFlarm Core Pure.

Bob

On Thu, 6 Aug 2015 03:26:08 -0700 (PDT), Andrew Ainslie
> wrote:

>https://buy.garmin.com/en-US/US/in-the-air/sport-aviation/gps-20a/prod525504.html
>
>$900 is almost affordable to make my trig tt22 adsb compliant under the new
>experimental rules. Interesting to see if anyone comes out with anything even
>cheaper.

[Darryl Ramm]

On Thursday, August 6, 2015 at 8:02:41 PM UTC-7, Bob Gibbons wrote:
> Just curious, what would be the advantage of this unit over using the
> 1090ES out capability of the GPS source in a PowerFlarm?
>
/snip/

Let be clear on terminology. The PowerFLARM itself has no 1090ES Out capability. it has a NMEA GPS Output that can be connected to some ADS-B Out devices, including Mode S/1090 ES Out transponders like the Trig TT-21/22.

You ultimately can't use the GPS source in the PowerFLARM to drive ADS-B Out and get all the ADS-B benefits. Doing that will not meet any 2020 Carriage Mandates (for power aircraft, or possibly glider corner cases like Class A airspace), and not if you want to receive ADS-B based ground services.

You certainty cannot install ADS-B Out in a certified aircraft, including glider, with anything like a PowerFLARM GPS source. And even if you do that in an experimental aircraft now you will likely start receiving letters from the FAA cautioning you about operating a non-compliant ADS-B Out system.

PowerFLARM does not even speak the a necessary serial GPS protocol to enable use for a ADS-B GPS data source (you need "Aviation format", not NMEA), let alone have all the RAIM support needed to meet TSO-C145c type requiremnts. (TABS class B GPS sources would reduce those requirements.. if TABS is adopted, and if it's installation/use regulations are sensible).

Nothing stops somebody today with an *experimental* glider connecting an NMEA GPS source to an ADS-B Out device as long as parameters like SIL are correctly set to indicate the degraded GPS source. And proper installation tests etc. are done. But you better know what you are doing, and be aware of the implications.

[Darryl Ramm]

On Thursday, August 6, 2015 at 8:02:41 PM UTC-7, Bob Gibbons wrote:
> Just curious, what would be the advantage of this unit over using the
> 1090ES out capability of the GPS source in a PowerFlarm?
>
> Both non-TSO'd, $790 for a PowerFlarm Core Pure.
>
> Bob
>
> On Thu, 6 Aug 2015 03:26:08 -0700 (PDT), Andrew Ainslie
> > wrote:
>
> >https://buy.garmin.com/en-US/US/in-the-air/sport-aviation/gps-20a/prod525504.html
> >
> >$900 is almost affordable to make my trig tt22 adsb compliant under the new
> >experimental rules. Interesting to see if anyone comes out with anything even
> >cheaper.

And saying "non-TSO'ed" is fairly confused/confusing.

Non-TSO'ed here used by avionics manufacturers really means it "meets performance requirements of" some TSO, but is not actually TSO'ed.

You have to look at the specs the device actually meets even though it is not built to a TSO. Garmin here are less than clear on this. They talk fuzzily about things like "meets the 2020 Carriage mandate requirements". Which in this case basically will mean TSO-C145c. In some cases a non-TSO product from vendors is identical to their other TSO products just without a TSO label and usually at a significantly lower price.

PowerFLARM does not meet the requirement of any TSO of any type. To say it is "non-TSO" is true in a way, but really a meaningless statement in the normal way it is used to describe avionics.

[Bob Gibbons[_2_]]

Darryl, thanks for the clarification.

Bob

On Thu, 6 Aug 2015 20:52:33 -0700 (PDT), Darryl Ramm
> wrote:

>On Thursday, August 6, 2015 at 8:02:41 PM UTC-7, Bob Gibbons wrote:
>> Just curious, what would be the advantage of this unit over using the
>> 1090ES out capability of the GPS source in a PowerFlarm?
>>
>> Both non-TSO'd, $790 for a PowerFlarm Core Pure.
>>
>> Bob
>>
>> On Thu, 6 Aug 2015 03:26:08 -0700 (PDT), Andrew Ainslie
>> > wrote:
>>
>> >https://buy.garmin.com/en-US/US/in-the-air/sport-aviation/gps-20a/prod525504.html
>> >
>> >$900 is almost affordable to make my trig tt22 adsb compliant under the new
>> >experimental rules. Interesting to see if anyone comes out with anything even
>> >cheaper.
>
>And saying "non-TSO'ed" is fairly confused/confusing.
>
>Non-TSO'ed here used by avionics manufacturers really means it "meets performance
>requirements of" some TSO, but is not actually TSO'ed.
>
>You have to look at the specs the device actually meets even though it is not built to
>a TSO. Garmin here are less than clear on this. They talk fuzzily about things like
>"meets the 2020 Carriage mandate requirements". Which in this case basically will
>mean TSO-C145c. In some cases a non-TSO product from vendors is identical to their
>other TSO products just without a TSO label and usually at a significantly lower price.
>
>PowerFLARM does not meet the requirement of any TSO of any type. To say it is
>"non-TSO" is true in a way, but really a meaningless statement in the normal way
>it is used to describe avionics.
>

[Darryl Ramm]

On Thursday, August 6, 2015 at 9:11:17 PM UTC-7, Bob Gibbons wrote:
> Darryl, thanks for the clarification.
>
> Bob
>
> On Thu, 6 Aug 2015 20:52:33 -0700 (PDT), Darryl Ramm
> > wrote:
>
> >On Thursday, August 6, 2015 at 8:02:41 PM UTC-7, Bob Gibbons wrote:
> >> Just curious, what would be the advantage of this unit over using the
> >> 1090ES out capability of the GPS source in a PowerFlarm?
> >>
> >> Both non-TSO'd, $790 for a PowerFlarm Core Pure.
> >>
> >> Bob
> >>
> >> On Thu, 6 Aug 2015 03:26:08 -0700 (PDT), Andrew Ainslie
> >> > wrote:
> >>
> >> >https://buy.garmin.com/en-US/US/in-the-air/sport-aviation/gps-20a/prod525504.html
> >> >
> >> >$900 is almost affordable to make my trig tt22 adsb compliant under the new
> >> >experimental rules. Interesting to see if anyone comes out with anything even
> >> >cheaper.
> >
> >And saying "non-TSO'ed" is fairly confused/confusing.
> >
> >Non-TSO'ed here used by avionics manufacturers really means it "meets performance
> >requirements of" some TSO, but is not actually TSO'ed.
> >
> >You have to look at the specs the device actually meets even though it is not built to
> >a TSO. Garmin here are less than clear on this. They talk fuzzily about things like
> >"meets the 2020 Carriage mandate requirements". Which in this case basically will
> >mean TSO-C145c. In some cases a non-TSO product from vendors is identical to their
> >other TSO products just without a TSO label and usually at a significantly lower price.
> >
> >PowerFLARM does not meet the requirement of any TSO of any type. To say it is
> >"non-TSO" is true in a way, but really a meaningless statement in the normal way
> >it is used to describe avionics.
> >

No problems, all the ADS-B stuff is an unfortunate frigging mess... much more than it could have been.

[[email protected]]

Darryl, I don't know how you can manage to keep on top of all this ADS-B stuff without your head exploding but thank you for doing so! Whenever I try to make sense of it all it makes me want to give up flying and take up Tiddlywinks or something.

Out of curiosity, what performance parameters in the PowerFLARM system make it a "degraded" GPS source unsuitable for ADS-B out? I assume the system must be accurate enough for airborne traffic awareness and collision warnings as it has proven satisfactory in FLARM to FLARM situations.

[Darryl Ramm]

On Saturday, August 8, 2015 at 11:44:09 PM UTC-7, wrote:
> Darryl, I don't know how you can manage to keep on top of all this ADS-B stuff without your head exploding but thank you for doing so! Whenever I try to make sense of it all it makes me want to give up flying and take up Tiddlywinks or something.
>
> Out of curiosity, what performance parameters in the PowerFLARM system make it a "degraded" GPS source unsuitable for ADS-B out? I assume the system must be accurate enough for airborne traffic awareness and collision warnings as it has proven satisfactory in FLARM to FLARM situations.

Everybody keeps thinking first about GPS accuracy, accuracy is just a small part of what makes a high-end aviation GPS like a TSO-C145c device. It's reliability, failure detection and predictability of that reliability that separate these from consumer devices.

A TSO'ed/IFR GPS source used to meet the FAA 2020 Mandate such as TSO-C145c has to support RAIM for reliability purposes. PowerFLARM's consumer chipset based GPS source cannot do that.... and RAIM and other goodies are not transmitted over NMEA. TABS/TSO-C199 Class B GPS sources do away with the RAIM requirement (it's actually one of the big good things in that TSO).


TABS/TSO-C199 Class A (the transponder/1090ES Out part) use HFOM (Horizontal Figure of Merit) and VFOM (Vertical Figure of Merit) for "GPS health", but NMEA does not send HFOM or VFOM data. That is why the TSO allows the Class A TABS device to calculate HFOM and VFOM from HDOP and VDOP which NMEA does provide (in $GPGSA). Or course a TSO-C199 Class B device might use NMEA, Aviation serial, NexNav serial binary, etc.

It's worth noting that the first GPS product announced that is targeted at TABS Class B GPS source use is the NexNav Micro-i, and few details are available so far, but I expect it will transmit GPS data on both NexNav serial binary and NMEA serial links as their similar products do, and it does include RAIM support (which would require use of the NexNav binary serial link.... which the Trig TT-21/22 already support) even though that is not required for TABS... NexNav have likely largely just repackaged another of their products at reduced price.