On Monday, May 21, 2018 at 9:50:09 AM UTC-7, Paul Agnew wrote:
Fuel for the fire. I found this letter from the FAA Milwaukee FSDO in response to an inordinate number of Form 337s being filed for radio installations. It may be old, but I don't know of any change in policy since the date of the letter regarding 337s.

https://groups.google.com/forum/#!to...lt/qodHhczVS1Y



U.S. Department of Transportation
Federal Aviation Administration
Flight Standards District Office
4915 South Howell Avenue
Milwaukee, WI 53207

DATE: June 5, 1995

SUBJECT: Major Alterations

TO: Certified Repair Stations and Inspection
Authorization (IA's)

This office is frequently confronted with questions regarding
what constitutes a major alteration, especially when
installation or removal of avionics and other similar
equipment is involved. The following information is provided
to help mechanics and repair stations understand this
sometimes complicated matter. The regulatory definitions of
major alterations are found in Federal Aviation Regulations
(FAR) 1 and 43, Appendix A (a). These regulations are often
interpreted too conservatively resulting in minor alterations
being treated as major alterations.

Simple alterations that do not affect the structural
integrity of the aircraft, alterations that are made by the
same method as the aircraft manufacturer has used or
installation of equipment listed by the aircraft manufacturer
as "Optional Equipment" may be considered minor alterations.
A simple equipment installation that is made in an aircraft
with units mounted on factory provided racks may be
considered as minor alterations. The certificated person
installing the equipment is responsible to use the
information provided by the equipment manufacturer, and that
information in Advisory Circular (AC) 43.13-1 and 43.13-2
regarding wire size, circuit protection, wire support,
antenna installation, etc. They are also responsible to
record the alteration in the aircraft records in accordance
with FAR 43.9 (logbook entry) and update the weight and
balance and equipment list.

We do not wish to imply that field approvals of equipment
installation is never required. Examples of installations
that would require field approval a

* Alterations that involve the construction of a radio rack
or shelf.

* An installation made in an instrument panel that is a
structural part of the aircraft and requiring an opening
to be cut in areas other than that specified by the
aircraft manufacturer.

* Special FAA policy sometimes requires field approval on
installation of new types of equipment such as the current
requirement for GPS.

If you have any questions regarding this memo, or are in
doubt as to whether a 337 is required, please do no
hesitate to contact this office.


Sincerely,

Thomas L. Lind
Supervisor, Airworthiness
Certificate Management Unit

The FAA has done a reasonably good job of outlining what's required, but they have thrown in a few head scratchers.

It's referenced in their 2016 Memorandum regarding Installation Approval for ADS-B Out Systems. The memo's available from this FAA webpage https://www..faa.gov/nextgen/equipadsb/installation/ Click on the link to AFS-360_2016-03-02.pdf

Reader's digest version:

- Pairings of transmitters / GPS source must be approved. Pairings are not specific to any particular aircraft. "Once the performance of the initial pairing has been established, the FAA considers follow-on installations of the same pairing to be approved". This means in any aircraft. Gliders are aircraft and nothing glider specific is required or desired.

- This is a minor alteration unless installation of antennas penetrating pressure vessels is required, etc. There's a good flow-chart outlining this on the last page of the PDF.

The FAA asks that ADS-B Out installations on CERTIFIED aircraft be documented with an advisory 337 submitted directly to OK City (NOT the local FSDO). This confuses folks since the 337 title says "Major Repair and Alteration", but we're not doing a major alteration. Cognitive dissonance anyone.. Anyways, just go with it. The FAA had to figure out a way to track who's installing ADS-B and that's what they chose. It's NOT a major alteration for any glider that I can think of. The feds even give you the specific language to enter on the 337. Again, just go with it.

Let's stay with the specific guidance the FAA has provided regarding ADS-B Out installations and not get wrapped around the axle of what we believe are conflicting regs. As with any bureaucracy there will be lack of clarity at times and cases where regs conflict. Let's not make it worse by running it through the RAS mill.

Cheers,
Craig