On Thursday, May 16, 2019 at 12:11:07 PM UTC-7, Jj wrote:
I agree completely, thats why I dont understand the use of a 337.

I gave you the FAA document that directs A&P on what to do, **you need to read it**. It tell you exactly what you are asking, and even includes instruction on how to complete the 337. Dan's A&P did exactly that after I pointed them at this policy.

The practical use of the 337 here where it's not a major alteration is so the FAA can track ADS-B Out installations. The ADS-B Out hardware does not transmit information about what it is, or what GPS is attached to it, and I expect the FAA wants to know.. especially to look for what hardware installs have problems or what A&P installers are creating problems.

The FAA has evolved ADS-B out installs significantly, initially they all required approval in type certified aircraft, now it's just a 337 notice to record the install unless it otherwise requires approval. The other thing that was found/obvious was the tight dependency between GPS source, ADS-B Out hardware and the ability to only pair some devices, and the need to follow precise instructions for that pairing. That is why the FAA requires use of STC to justify that pairing (and provide the installer with relevant setup instructions). That STC is not otherwise required.. which is how it can be used here if the aircraft is not in the AML.

With an experimental install there is no need to follow this policy, so don't provide the 337 to the FAA. And the "meets blah blah..." wording in 14 CFR 91.227 allows use of a lower cost TN72 instead of an actual TSO-C145c TN70. But I hope the FAA is able to capture lots of similar information about installed hardware in the public ADS-B performance report request form.