On Monday, June 4, 2018 at 7:38:18 AM UTC-7, Charles Longley wrote:
I don’t know if I agree with you. If an ADSB out can be installed in any type certified aircraft without a 337 why do the manufacturers bother with a STC? I’ve installed a Stratus transponder in a Pawnee using the policy you quoted. I didn’t consider it an informational 337 when I did it. The FAA gets information on which airplanes have ADSB when they’re flown in the national airspace system.

Experimental aircraft are a whole different subject.

This has been flogged to death on r.a.s. in the recent past, and the person who was then confused about it went to his FSDO, which confirmed what I was saying. But I'll spare your the pain of wading though that tangled ball.

I did try to addressed exactly the reason an STC is usually needed in the post before. The STC is needed (as the easiest way) to establish a valid pairing between a ADS-B Out tranmitter (e.g. transponder) and a GPS source. You are expected (by that FAA policy) to follow that STC for the configuration related to that device pairing (or if a single box, presumably the setup in that box related to the GPS source). This stuff is in pretty clear English (especially section (6)) of the FAA policy doc I gave you the link to.

You are not required to treat the install as a major alteration and to use that STC for an approval basis just because this is an ADS-B install (if you think you are please explain exactly what establishes that). If you otherwise determine the install is a major alteration then an STC specific to the install in that aircraft is going to provide the basis for a field approval, and you would file a 337 with the FSDO. If it's not a major alteration then you just need an STC that establishes the pairing of those devices, and it does not need to be specific to that aircraft.

Manufactures here clearly need STCs for the pairing basis. Manufacturers also need some STCs for installs as a major alteration approval basis because well those installs are really major alterations, manufactures also like to have STCs to cover stuff where they may not really raise to the level of major alterations but some A&Ps (and FSDO staff) might be nervous about doing stuff without an STC. Many of the existing install STCs were also developed in the past where the installs process was more complex.

The FAA cannot get information they want from the equipment installed in aircraft from direct monitoring of the ADS-B Out signal. There is no data transmitted over ADS-B Out that describes the transmitter or GPS source manufacturer or model (I wish there was), and no way to collect from that the magic info of which A&P signed off on the install. Which given how many ADS-B Out install fail from basic setup/software configurations I suspect they want to know and track down those responsible--to help avoid more, the FAA seems to be being very supportive/helpful with installs but there are so many problems with installs for them to track down. Since an ADS-B Out install is not necessarily a major alteration a 337s would not necessarily be filed with the FSDO so the FAA is seeking a way here to collect all this information and using a 337 form in an unusual way to do that. They would never have bothered with creating that extra process if all installs were major modifications with 337s going to the FSDOs.

I hope you did followed the process the FAA expects for the ADS-B Out equipment you installed in the Pawnee. If you also decided that install required a major alteration approval for other reasons then that that was your decision. I hope you submitted the "notification only" 337 to Oklahoma, if not you may want to go ahead and do that. Not doing that might eventually get the club a "please explain" letter.