On Saturday, September 23, 2017 at 7:33:27 PM UTC-7, Dave White wrote:
If I read the Trig website correctly the tt21 is approved for adsb-out just about everywhere on the planet except the USA. So if someone brings their certified glider from their home country are they legal to fly in the USA or must they comply with USA requirements?

Is there light at the end of this rat hole? But the answer is going to be comply with US regulations. The more detailed answer of course is you are going to discuss this with an FAA representative.

And there is no such thing as just a TT-21 install for ADS-B out.What is the GPS source? I expect many gliders flying outside the USA who have ADS-B Out have a COTS GPS source, and that likely a worse issue, who knows what they set SIL etc. to. Not only will that not be valid in a certified equivalent aircraft in the USA but it may well get you noticed by the feds.