Garmin GPS20-A with Trig TT-31

[RV7Grinner]

Question: Will the Garmin GPS 20-A provide a "Compliant" signal to a Trig TT-31 Extended Squitter Transponder?
I have spoken to Garmin twice and they don't seem to know. I just had a vigorous debate with a national avionics supplier as I tried to order the 20A and he believes that the 20A with the TT-31 will NOT be 2020 compliant (knowing that it is installed in an EAB airplane). I believe that the TT-31 speaks the proprietary Garmin RS232 plus language so what am I missing?
Thanks for any understanding you can provide.

[az_gila]

Originally Posted by RV7Grinner

Question: Will the Garmin GPS 20-A provide a "Compliant" signal to a Trig TT-31 Extended Squitter Transponder?
I have spoken to Garmin twice and they don't seem to know. I just had a vigorous debate with a national avionics supplier as I tried to order the 20A and he believes that the 20A with the TT-31 will NOT be 2020 compliant (knowing that it is installed in an EAB airplane). I believe that the TT-31 speaks the proprietary Garmin RS232 plus language so what am I missing?
Thanks for any understanding you can provide.

I think Garmin (or Trig) has to specifically tell you about the combination -

The FAA recommends a WAAS GPS that is compliant with TSO-C145 or TSO-C146. These units are readily available for general aviation and provide sufficient performance to meet the 14 CFR 91.227 requirements. Avionics vendors offer stand-alone GPS receivers and package them with ADS-B transmitters or with GPS Navigators. Mixing and matching GPS systems with ADS-B transmitters in the field is not permitted unless the equipment pairing was shown to be compatible via a previous certification effort with the FAA (for example, an STC). Be sure to contact your manufacturer if you are unsure which GPS systems are approved for your ADS-B transmitter.

- from here -

https://www.faa.gov/nextgen/equipadsb/installing/

[RV7Grinner]

Thanks Fred, I guess that makes sense. I am having trouble with Garmin's statement that their GPS 20A..."Meets WAAS/SBAS position source requirements for ADS-B ?Out? and is Compatible with a wide range of 1090 ES transponders." What 1099 ES transponders are they possibly referring to besides their own?
Again, I am not looking for a "certified" combination, only a 2020 compliant combination.

[BobTurner]

I think to cover all bases you need Garmin to say, "The ADSB+ output from this (GPS-20A) device is exactly the same as that from a Garmin 430W".
The 430W is on Trig's compatible list.

[g3xpert]

Originally Posted by RV7Grinner

Thanks Fred, I guess that makes sense. I am having trouble with Garmin's statement that their GPS 20A..."Meets WAAS/SBAS position source requirements for ADS-B ?Out? and is Compatible with a wide range of 1090 ES transponders." What 1099 ES transponders are they possibly referring to besides their own?

Hello Bruce,

Any 1090ES transponder that is currently compatible with the ADS-B+ RS-232 Output of a GTN 6XX/7XX or GNS 4XXW/5XXW will also be compatible with the same output from a GPS 20A.

The GPS 20A also meets all of the applicable TSO performance requirements for a 14 CFR 91.227 compliant position source (again, same as the certified GTN).

This FAA guidance for homebuilts is probably most useful. It provides this guidance:

For uncertified equipment, the owner should obtain a statement of compliance from the supplier, along with installation instructions, that identifies that the ADS-B equipment complies with section 3 requirements of the applicable TSO and that, when installed in accordance with the installation instructions, complies with the aircraft requirements of 14 CFR 91.227.

If a transponder manufacturer is presently able to provide a statement of compliance when connected to a GTN (installed per the GTN installation manual), then it seems reasonable that they may also provide a similar statement of compliance when using a GPS 20A installed per its installation manual.

Garmin has only tested the GPS 20A with Garmin transponders, but we know of no reason why other 1090ES transponders capable of using the ADS-B+ interface cannot achieve similar results.

Thanks,
Steve

[RV7Grinner]

Thank you Steve!
I will pursue a statement of compliance from Trig but it is great to hear that the output of the 20-A is identical to your certified GPS units. I appreciate the help

Bruce

[Feetwet]

Please keep us posted. I have a TT-31 installed in my RV4, and plan to use the 20A for the 2020 ADS-B out requirement as well.

[jantar]

Originally Posted by RV7Grinner

Thank you Steve!
I will pursue a statement of compliance from Trig but it is great to hear that the output of the 20-A is identical to your certified GPS units. I appreciate the help

Bruce

Any news on this subject. Did anyone got confirmation from Trig if Garmin 20A will interface in a compliant manner?
From Trig T22 installation manual "Garmin ADS-B protocol, including ADS-B plus" are supported protocols and you can select.

The Trig STC specifies GTN6XX and GTN7XX sources as well as GNS 4XX and 5XX sources.
I guess the question is does Garmin 20A sends exactly the same messages as GTN6XX allowing to select these sources in Trig software? Steve, is that certain?

Thank you.

[g3xpert]

Originally Posted by jantar

I guess the question is does Garmin 20A sends exactly the same messages as GTN6XX allowing to select these sources in Trig software? Steve, is that certain?

Hello,

Yes, as stated above "Any 1090ES transponder that is currently compatible with the ADS-B+ RS-232 Output of a GTN 6XX/7XX or GNS 4XXW/5XXW will also be compatible with the same output from a GPS 20A. ".

Thanks,
Steve

[jantar]

Originally Posted by g3xpert

Hello,

Yes, as stated above "Any 1090ES transponder that is currently compatible with the ADS-B+ RS-232 Output of a GTN 6XX/7XX or GNS 4XXW/5XXW will also be compatible with the same output from a GPS 20A. ".

Thanks,
Steve

Steve, could you point me to an install manual for Garmin 20A.

I just checked my Trig transponder's configuration options in the software and the only selection available is Garmin ADSB, which means there is not a different setting for different hardware. This is good as it means the instruments probably use exactly same protocol.