ADSB out in tow planes

What’s an informational 337? Never heard of one until now.

Charlie
A&P/IA

On Sunday, June 3, 2018 at 7:21:37 PM UTC-7, Charles Longley wrote:
What’s an informational 337? Never heard of one until now.

Charlie
A&P/IA

Don't worry, you are not alone, this has caused a reasonable amount of confusion and not just with gliders. Have a read of FAA 8900.362 - Policy for Installation of ADS-B OUT Systems. https://www.faa.gov/regulations_poli...mentID/1029526 (no that policy really has not expired).

An "information only" 337 is what the FAA wants you to complete and send to FAA HQ in Oklahoma for an ADS-B out install. It's so they can track what is being installed. It's not the normal use of an 337 sent to the FSFDO for field approval for a major alteration. This has been discussed here in detail before in the thread linked in previous posts. There are multiple other FAA reference docs giving the same guidance listed in that other thread. The FAA may not formally refer to these as "information only" 377 but thats a term used by others, and by FAA folks when you talk to them.

The misconception that an ADS-B out install is by necessity a major alteration and requires a 337 (to the FSDO) has seemed to cause some glider owners unnecessary pain. Folks get confused and send the 337 to the FSDO and then the FSDO assumes they are seeking field approval for a major alteration, and you end up with folks trying to jump through hoops and find STC etc. and other items for install in a glider that are likely not required in the first place. And the pain starts with: there are no STCs for any transponder install in any glider. None, nada, zilch. And if you read the above policy, you'll see the STC mentioned, but it explains that is also a special case for an ADS-B Out install--the STC there is only required to establish the pairing of a particular transponder and GPS source, not the basis for a design approval for a major modification.

Since this confusion has created issues for some owners my effort to explain it here was is to avoid others suffering. Of course if an A&P IA has good reason to determine if any install actually is a major modification then that's a different discussion. Most installs of avionics in gliders are not considered major modifications, and the FAA has been supportive of that position, and there is no regulation that makes ADS-B Out installs special cases where they are automatically major alterations. The other thing I've suggested people do is let their A&P IA seek any clarifications about these from the FAA instead of trying to contact FSDO staff themselves.

There is no FAA notification required for ADS-B Out installs in experimental aircraft and none required for TABS/TSO-C199 (read that TSO for more info) install in any aircraft since 14 CFR 91.225/91.227 (the only thing that policy above applies to) don't apply to TABS... that's another whole point of potential confusion with owners or A&P contacting the FSDO and asking about "ADS-B Out" installs where they mean TABS and the FSDO will likely assume 2020 Complaint systems not TABS, and staff there may just not know what TABS is at all. And now we have at least one glider owners who has got an ADS-B Out non-compliance letter from the FAA for their TABS systems because the FAA ADS-B Out compliance reporting does not understand TABS. I'm helping respond to that letters (and can provide a draft of the response letter to anybody who wants one) and I hope this is a great opportunity to help educate more FAA folks on TABS and gliders in general.

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.

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.

Did you not read my post? I said I sent a 337 in per the FAA’s guidance. I disagree with you that it was a “notification� 337. But everyone is entitled to their opinion.

On Monday, June 4, 2018 at 7:07:57 PM UTC-7, Charles Longley wrote:
Did you not read my post? I said I sent a 337 in per the FAA’s guidance. I disagree with you that it was a “notification� 337. But everyone is entitled to their opinion.

I read your post, very carefully, and its not clear what you have done. Did you send a 337 to Oklahoma or the FSDO? Did you treat the installation was a major modification, and if so would you mind explaining why? Did you get the FSDO to approve Block 3 before sending it to Oklahoma? Did Oklahoma send you back the 337 with Block 3 approved? I appreciate your help here explaining exactly what you did, I suspect we may be talking at crossed purposes.

I again want to reiterate that ADS-B Out installations in gliders (I know you did a towplane) should normally be minor modifications, and therefore do not need major modification approval, but do require a "notification only" 337 filed with FAA HQ.

I followed FAA guidance and installed a Stratus transponder with its associated GPS antenna in accordance with the STC. The STC only has a few models in it not including the Pawnee. I filled out the 337 per FAA guidance and sent it off to OK City. It wasn’t a field approval but was a Major Alteration so no need to send it to the local FSDO. Again per FAA guidance. I don’t expect to get the 337 back. I expect it to just be filed with the aircrafts records as usual.

To reiterate there is no such thing as a “notification� 337..

I haven’t been asked to or researched putting an ADS-B out transponder into a glider so I can’t really speak to that. When I install the PowerFLARM brick into my glider in the fall I’ll get the ADSB out option and do the appropriate research/ paperwork.