On Monday, November 25, 2019 at 8:39:51 PM UTC-8, wrote:
On Sunday, November 24, 2019 at 4:51:37 PM UTC-8, wrote:
On Sunday, November 24, 2019 at 10:56:03 AM UTC-5, Dave Nadler wrote:
On Friday, November 22, 2019 at 3:01:42 PM UTC-5, wrote:
I have heard gossip of ... leak issues.

Cure for squat leaks: https://tinyurl.com/ycvg3to4

Well, that depends.

Can someone point me to the regulation that requires an experimental glider to install a squat switch along with adsb?

There is no regulation that says that. Nobody here (including me) has ever claimed there is AFAIK.

The relevant bit is hidden in 14 CFR 91.227 (d)(1)

...Minimum Broadcast Message Element Set for ADS-B Out. Each aircraft must broadcast the following information, as defined in TSO-C166b or TSO-C154c......

(1) The length and width of the aircraft;

Length and Width of the aircraft are only transmitted in ground mode messages. So this regulation says for 2020 Compliance the system must be capable of switching to ground mode. But I (and others) interpret the intro wording "each aircraft must..." as a direction that this change must be automatic. It's not saying each aircraft must be capable of being put in air/ground mode by a pilot. It's saying the aircraft must... Now it's sure not very well worded but that requirement is how manufacturers including Trig are interpreting that clause.

How do you as an installer propose to meet 14 CFR § 91.227 (d)(1)?

This is something the FAA clearly cared about as RTCA DO-260 (that defines 1090ES Out) actually intended light aircraft 1090ES Out to be able to stay in airborne mode while on the ground. The FAA deliberately changed that in these regulation, likely with concern about integration with ADSE-X and ASSC ground management systems. Which uh is really unlikely to be an issue with gliders.

The worse thing to do is to use the GPS air/ground determination mode in gliders that may fly in wave, or even strong headwind. Flying around spewing ground mode messages will eventually get you a letter from the FAA. How different traffic/collision avoidance systems behave when they see an erroneous ground mode targets is too complex to guess, but likely not good.

Not ever transmitting a ground mode message might well have no practical impact in typical glider operations. Few gliders are landing and taxing around SFO or JFK. But gliders do operate at some busy airports at times and you want to be careful of possible interactions with a variety of traffic systems in other aircraft. Some airports also have ADS-B coverage down to ground level and in those cases the FAA might followup up with any SIL=3 ADS-B Out systems that is not switching to ground mode. But not being a likely practical issue and not meeting regulation requirements are two separate things.

So it's *my recommendation* that 2020 Compliant ADS-B Out installations in all glider use a pitot squat switch.

If the glider is type certificated your A&P IA should follow the instructions in the TT22/TN70 STC. Not all of that STC is directly relevant to glider installs, but it does call out a the pitot squat switch (luckily it does not mandate the GPS air/ground mode determination).

If would hope A&Ps installing ADS-B out systems in experimental gliders are discussing how this works with owners, whether they are installing a pitot/squat switch or not, checking the operation of this systems (e.g. confirming the TT22 automatically display flips from ON to ALT as the glider takes off). and making sure the owner understand how to use whatever they have installed. FAA ADS-B Performance Reports will flag ground mode when airborne errors and airborne mode when on ground errors (although in many cases the FAA receiver towers will will not see your aircraft on the ground). If you install any of this stuff and it routinely has problems, expect the FAA to eventually followup with you.

If you are doing this yourself.... how do you propose to meet 14 CFR § 91.227 (d)(1)? What will the the person who signs off the glider's annual condition inspection expect to see for 91.227 compliance?

Squat switches are really a subtler things here, so many ADS-B Out installations have other more fundamental problems because A&Ps or owners doing work are not being careful with basic software setup. That can include not working at all, working, but not well enough to be seen by ATC, etc. You have to test each install by pulling an FAA Public Performance Report. The TT22 just saying it has a position fix is not enough to know things are working OK. I hope A&Ps are requiring owners to do an ADS-B Out test flight of all experimental gliders they work on, even if not called out in FAA policy (like it is for type certified aircraft). The FAA ADS-B Out Public Performance Report has been updated to request the submitter asking for the report to note who did the installation. The FAA seem to be exceedingly helpful with ADS-B Out problems, but pay attention.

TABS/TSO-C199 specifically allows the aircraft to stay in airborne mode on the ground. So for a TABS install I would argue the best thing to do is can just leave the pitot switch set to "none" and let the pilot manually select ALT. TABS also broadcast at a lower SIL level and not visible to ATC and not intended to interact the same with things like ADSE-X and ASSC.