IFR GPS in an experimental aircraft

There has been discussion about what is required to equip an experimental aircraft for IFR flight. On the topic of transponder and altimeter checks, the question has been answered pretty well in these threads:
http://www.vansairforce.com/community/showthread.php?t=36016
http://www.vansairforce.com/community/showthread.php?t=34369

However, I haven't yet seen an authoritative answer on what is required for an IFR GPS installation. I'm facing this question now in our RV-6 and I would like to know what are current best practices in the experimental community on this topic.

Here's what I think I have figured out so far, in the context of our Apollo GX60 IFR GPS/COMM, followed by questions I would really like to find the answer to!

1. The 2008 AIM 1-1-19-d says that conducting any GPS operation under IFR requires:

... that the equipment meet TSO-C129,
... the installation be done in accordance with Advisory Circular AC 20-138,
... "The GPS operation must be conducted in accordance with the FAA-approved aircraft flight manual or flight manual supplement."

2. The GX60 is a TSO-C129a, class A1 GPS, so the TSO requirement is met. (We also have all the remote CDI, annunciators, etc. that are required.)

3. Advisory Circular AC 20-138A (linked here), supersedes 20-138. One change in the new version is that a GPS installation can now be considered a minor alteration, if manufacturer's instructions are followed (used to require a STC, for aircraft that have a TC). (See paragraph 8.)

4. AC 20-138A also, in paragraphs 22 and 23, lists ground and flight tests. These seem like the sort of thing you would actually want to have done before launching into the clouds.

5. The GX60 installation manual says: "This article may be installed only if further evaluation by the applicant documents an acceptable installation and is approved by the Administrator. Source: FAA TSO-C129a, GSO-C37d, TSO-C38d, and TSO-C128."

6. Apollo (aka II Morrow aka UPS aka Garmin) provide an editable sample AFM supplement (in their "STC kit", linked here) to customize to your GX60 installation. The front page has blanks for FAA signature (name, title, office).

So here are my questions:

A. Since STC's and 337's don't apply to experimental aircraft, a lot of AC 20-138A is not directly applicable. Is this a correct assumption?

B. However the ground and flight tests at least seem like a good idea. Are these typically documented in an experimental IFR GPS installation, and if so what form does the documentation take?

C. Offhand I don't see a way that experimentals are exempt from the requirement of an AFM supplement. Am I missing something? It would be pretty easy to create one for our GX60 installation, starting with the sample, but I don't know about the feasibility of getting an FAA signature on it. Anybody actually done that, or can give me a black-and-white argument for why it's not required?

Thanks in advance for the help!

--Paul
RV-6 N976DP

To followup on my own post here...

I emailed [email protected] with my questions and received the following response (excerpted with permission):

"Your outline is pretty much spot-on. You have met the requirements in
accordance with the AIM and AC 20-138A. The sample flight manual that
comes with the unit should be used, modified as necessary to meet the
specifics of your installation. Since there is no FAA approved manual
of any kind for an amateur-built aircraft, the one that is supplied by
the GPS manufacturer is the best you can do. The FAA will not offer any
further approval."

I hope this is of some help to others who may be concerned about similar issues.

--Paul

Great job

Thanks for taking the time to research and post this!

Flight/Ground Tests

Paul,

I went through this process with my -8 a few years ago. The Washington FSDO claimed I needed both the flight and ground tests. That wasn't a big deal but they also said an IA would need to perform the flight test. After a bit of discussion, together we contacted the FAA HQs in DC. They advised that yes, the two tests are required for an experimental but that it was acceptable for me to perform the tests. As a result I have the two test documents that I'd be happy to share. They're for a GNS-430 but I suspect can be easily modified. By the way, I got the draft copy of the tests from the shop where I purchased the unit.

Rick, Yes I'd be interested in seeing those docs. The installation manual for the GX60 has a checklist that they say satisfies AC 20-138 (not 20-138A, which came later). But it includes only ground tests. I was going to make up my own checklist for ground and flight tests based on paras 22 and 23 of 20-138A and go with that. But I'd like to see what the GNS-430 uses.

--Paul

IFR 430 in Rv 8

I would like to get these documents. I have a 430 in my RV 8

Looks like good information

Jmwld

Paul,

I sent the documents to your work e-mail. Let me know if you'd like me to send them elsewhere.

If anyone else is interested please send an e-mail to [email protected] and I'll be happy to oblige.