Greg Esres wrote:

If you can retrieve it from a current database with an IFR
approach-approved GPS, it is legal to use. You will note the warning
message Garmin provides when you pull up and ILS approach.

I checked with the AIM again, and what it says seems on point:

-------Snip------
Do not attempt to fly an approach unless the procedure is...identified
as "GPS" on the approach chart...The navigation database may contain
information about nonoverlay approach procedures that is intended to
be used to enhance position orientation, generally by providing a map,
while flying these approaches using conventional NAVAIDs.
-------Snip-----

Garmin's position, as you know, is that you aren't "established" on
the approach until you're on final. Are you aware of any
justification for this position at all?

I think I have covered it, but let me try again: for purposes of TERPS
and regulatory requirements to be established, an IAP can begin as early
as a feeder fix (before an IAF, where there is a feeder fix).

For purposes of the specifications for IFR GPS avionics, the "approach" is
*only* the final approach segment. The other segments are terminal
routes, and use terminal CDI scaling/sensitivity/RAIM. Only the approach
mode uses approach scaling/sensitivity/RAIM.

You won't find a regulation that says this, nor will you find an FAA
document that proclaims this to pilots. Nonetheless, all TSO-C129
avionics and all higher-end LNAV/FMS platform treat the final approach
segment as the "approach," per se.