TT21/TN72 power consumption

On Friday, May 25, 2018 at 6:56:15 PM UTC-7, wrote:
I used the settings Richard just provided in my experimental glider and the ADSB report showed no errors. You do need both the core and the display of the TT22 to be updated to the latest versions to see the options listed.. Also really nice is the GPS based squat switch option that is now available.

Thud. Sound of me beating my head against the wall.

Be careful, those settings Richard/Craggy Aero provided (and I helped write up) never say to set the squat switch to AUTO (to use GPS airspeed based air/ground determination). It may not be clear but the only intent there was you either use NONE (for TABS/SIL=1) or use a real physical pitot switch for SIL=3/2020 compliant installs (in which case you pick the option for a physical "swat" switch). Maybe a warning not to use AUTO needs to be there.

There is not really anything nice about the GPS squat switch and I don't know how many times I need to warn about that. I wish Trig would throw that crap out and provide pitot pressure switches with all their TN72 units sold for gliders. The AUTO (GPS groundspeed) mode in the Trig transponders is very easily fooled by low groundspeed seen in wave flights. Transmitting ADS-B ground messages while airborne is potentially a safety issue, certainly in violation of regulations, and will eventually get the FAA's attention, it will get flagged to FSDO staff who watch aircraft ADS-B issues. They have enough stuff to deal with with other aircraft transmitting bad ADS-B messages that the glider community does not need to add to it.

For SIL=1/TABS you do not need to broadcast ADS-B ground messages so set the squat switch in the menu to NONE (or not connected or whatever it's called). There is just no reason to ever use AUTO for SIL=1/TABS, there is no practical benefit at all for gliders and only bad things might come from that.

For SIL=3/2020 compliant installs, all aircraft are required to broadcast ADS-B ground messages when on the ground. Even though it's of likely no benefit to gliders in any practical scenario, and kinda silly, ... but since 14 CFR 91.227 (indirectly) requires ground messages to be broadcast we can't just disable it like we can do with TABS. I would not trust AUTO (i.e. use GPS groundspeed) at all, even in a glider that might really never be used for serious wave flights. As I've posted here multiple times before... for a SIL=3 install with the TN72 (which can only be done in experimental gliders and only with a TT22) I would use the pitot pressure switch that is provided in the TN70/TN72 STC kit (no you are not using the STC, you are just getting a known correct type of pneumatic switch and some tubing connectors in a kit).

I've worked with the main Trig glider dealers in the USA so they should be aware of this and know about ordering that STC kit (it's ~$150) and pretty trivial to install between the pitot and static lines behind the panel. Trig glider dealers selling pre-made cables to connect the TN72 to the TT22 also tell me they are including the extra wiring in their wiring harnesses for that pitot switch (but even without that it's simple to add, the SPST pneumatic switch shorts one TT22 pin to ground). I really hope that when customers buy a TN72 their dealers are talking with them about this and if they should buy that pitot switch kit or not.