Hi Paul,

Here is a post from a Garmin engineer about compatibility of the 20A with the Trig TT22.
http://www.vansairforce.com/communit...60&postcount=5

Here is the list of certified GPS WAAS sources on Trig's web page currently:
http://www.trig-avionics.com/support...b-stc-program/

Putting the two together, it seems likely the 20A is compatible with the Trig. However you would need Trig to say that is so.

The link to the FAA page in the Van's forum post explains what the FAA expects for experimental non-TSO'd GPS WAAS sources.

None of this applies to non-Experimental gliders. The 20A is not permitted, a TSO'd GPS source is required. Since gliders don't ever seem to make it onto "approved model lists" in transponder/ADS-B STCs, a field approval would be required.

That's my understanding at least. Any traffic in the area that knows better, please advise.

Sarah Anderson

On Tuesday, December 15, 2015 at 11:25:30 PM UTC-6, Paul Remde wrote:
Hi,

I'm gaining knowledge in ADS-B over the years. But I can't say I'm an
expert. I could use some feedback from some of the extremely knowledgeable
people that monitor this group.

I sell Trig TT22 transponders - which are FAA approved for ADS-B when used
with an approved GPS source. But currently approved GPS units are $3500+.
I have been hoping that a much lower cost GPS unit "designed to meet the
requirements..." would become available in the future - making it possible
to have FAA approved ADS-B out that meets the requirements for 2020.

This week a customer pointed out a solution - I think. It is the Garmin GPS
20A. It sells for $845. That is still a lot of money for a WAAS GPS, but
it is a lot better than $3500. I believe the antenna is extra.
https://buy.garmin.com/en-US/US/in-t...rod525504.html

The web site says that it is approved for ADS-B out in LSAs. It is not
clear to me whether it would be legal to use it with a TT22 in an
experimental, or non-experimental sailplane.

I believe that ADS-B will make our flying much more safe. I am angry that
the FAA requires $3500+ GPS units at this time. They are reducing safety.

I'm not trying to push ADS-B down the throats of anyone. I am just trying
to fill a need. Many gliders already have TT22 units and might consider
adding an $845 GPS, but not a $3500+ GPS unit.

Also, it is my understanding that "field approvals" are required when
installing ADS-B out systems in certificated aircraft. Would there be a lot
of expensive paperwork necessary to get FAA approval for a system that
includes a TT22 and Garmin GPS 20A?

Any thoughts?

Best Regards,

Paul Remde
Cumulus Soaring, Inc.