On Thursday, January 3, 2019 at 6:54:47 PM UTC-8, wrote:
I attended the the AOPA Fly-in at Santa Fe this year and spoke to both the Trig representative and some knowledgeable FAA folks about the ADS-B options for certified gliders vs. those with Experimental classification. The interpretation that the Trig 22 with the TN-70 is the only legal 2020 Compliant option for certified gliders came into question. After the FAA rep closely read the requirements, I was advised that the much cheaper TN-72 might be a viable choice. His interpretation indicated that a certified aircraft that is not absolutely required to install ADS-B Out (read: Glider), and does NOT have a generator fed electrical system would be considered legal with the TN-72.

Since this is the only time I have received this answer, and all other documentation I have seen indicates that an installation in a certified glider requires the more expensive TN-70. I would appreciate other input. Darryl Ramm seems to be the "go to guy" for ADS-B information. Your thoughts?

Please ask the folks telling you this how you get that opinion in writing and in a way usable by say an A&P to know they are OK. This is not something that a local FSDO is likely to make with, they pretty much focus on following AFS-360_2016-03-02. Once well outside that this is stuff for others.

So the argument goes... As PIC I'm not required to comply with 14 CFR 91.225 so 14 CFR 91.227 does not apply to me and so I don't need to follow AFS-360_2016-03-02... so I'll just go ahead. and install a SIL=3 output TN72 in a glider. My A&P does not need to file the ADS-B Out install 337 because that's a AFS-360_2016-03-02 policy requirement. And they don't have to follow that policy.... well if you can find an A&P who agrees with that... go for it. I can see the placard now "The ADS-B Out install in this aircraft does not comply with 14 CFR 91.217..." The FAA ADS-B monitoring system will likely quickly catch that there was no '337 filed for that SIL=3 install in a type certified aircraft and they'll want to know where/who did the install. So may be the quickest way fo find out the FAA's interpretation of all this :-) OK maybe not the wisest thing to do.

I'm not necessarily a believer that legal interpretation is correct, and this has never got to a court or FAA Office of the Chief Counsel for an opinion. A request to the Office of Chief Counsel for an interpretation would be the next step for an organization that cared about this. Even if the FAA agreed, not everybody will want to waive full 91.225 flight privileges. Some glider owners do want flight privileges in Class A, close above Class C or lowered Class B ceilings (e.g. Seattle), etc.

What is clear today in a type certified glider is the TN70+TT22 install with full AFS-360_2016-03-02 compliance get you everything. For other uses the TN72 SIL=1/TABS install is doable, but with reduced functionality. Part of the simple (non-legal) justification of the legitimacy of a TABS install, e.g. when explaining to FSDO staff, is the argument that the FAA created the whole TABS TSO-C199 approval to exactly allow this, and it's all simply orthogonal to 91.225 and 91.227.