Garmin 430 and ILS

The Garmin 430 documentation says that you can use the GPS for course
guidance on an ILS/LOC up until the final approach fix. Where exactly
does the approval for this come from? My inclination would have been
that in absence of an overlay, you could not use GPS anywhere after
the IAF.


Also, assuming this approval is legit, shouldn't this extend to a
non-overlay VOR approach?

Greg Esres wrote:

The Garmin 430 documentation says that you can use the GPS for course
guidance on an ILS/LOC up until the final approach fix. Where exactly
does the approval for this come from? My inclination would have been
that in absence of an overlay, you could not use GPS anywhere after
the IAF.


Garmin is correct. You don't need approach RAIM or approach sensitivity
until the beginning of a final approach segment for either a stand-alone
RNAV approach or an approved overlay.

So, you do not need localizer guidance until the P-FAF for an ILS approach
or the NPA FAF for a localizer approach. Because overlay is not approved
for a localizer, the localizer itself has to be used for the ILS or
localizer final approach segment.

The "flip-side" is also true, which is what Garmin states.


Also, assuming this approval is legit, shouldn't this extend to a
non-overlay VOR approach?

True, it could, but the vendors haven't seen that as a real-world issue.

Garmin is correct. You don't need approach RAIM or approach
sensitivity until the beginning of a final approach segment

I was sure they were, but I'm concerned about how to demonstrate this
correctness to others. The AIM says nothing about this.

I accept that flying the localizer outbound for the PT does not
require approach sensitivity and that the protected area is wide on
the initial segment, but I shouldn't have to know these things in
order to know what I can do with this box.

I'm mostly concerned with checkrides. Is there anything other than
Garmin documentation that can demonstrate this is a legal thing to do?

" non-overlay VOR approach?" True, it could, but the vendors
haven't seen that as a real-world issue.

I haven't done this in the real airplane, but on the simulator, the
box will advise changing to Vloc once established on the inbound
course of a VOR, but will not switch over. In fact, it goes down to
approach sensitivity, but doesn't indicate approach RAIM.

Would you argue that using the GPS for course guidance up to this
point is legal?


Thanks!

Greg Esres wrote:

Garmin is correct. You don't need approach RAIM or approach
sensitivity until the beginning of a final approach segment

I was sure they were, but I'm concerned about how to demonstrate this
correctness to others. The AIM says nothing about this.

I accept that flying the localizer outbound for the PT does not
require approach sensitivity and that the protected area is wide on
the initial segment, but I shouldn't have to know these things in
order to know what I can do with this box.

I'm mostly concerned with checkrides. Is there anything other than
Garmin documentation that can demonstrate this is a legal thing to do?

" non-overlay VOR approach?" True, it could, but the vendors
haven't seen that as a real-world issue.

I haven't done this in the real airplane, but on the simulator, the
box will advise changing to Vloc once established on the inbound
course of a VOR, but will not switch over. In fact, it goes down to
approach sensitivity, but doesn't indicate approach RAIM.

Would you argue that using the GPS for course guidance up to this
point is legal?

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.

You will note the warning message Garmin provides when you pull up
and ILS approach.

Yes, and I consider it to contradict what the manual says. The note
says for "monitoring" only, insinuating that approach guidance needs
to come from the underlying navaid at all times.

That's part of the reason I asked the question. I have difficulty
explaining away the inconsistency between the note and the
permissiveness of the manual.

On Sun, 13 Feb 2005 19:21:07 GMT, Greg Esres
wrote:

You will note the warning message Garmin provides when you pull up
and ILS approach.

Yes, and I consider it to contradict what the manual says. The note
says for "monitoring" only, insinuating that approach guidance needs
to come from the underlying navaid at all times.

That's part of the reason I asked the question. I have difficulty
explaining away the inconsistency between the note and the
permissiveness of the manual.

Same issues I'm attempting to work through in my thread "Yet more GPS
substitution questions", cept I was looking at a VOR/DME. I'll just
merge into this one - thanks.

Greg Esres wrote:

You will note the warning message Garmin provides when you pull up
and ILS approach.

Yes, and I consider it to contradict what the manual says. The note
says for "monitoring" only, insinuating that approach guidance needs
to come from the underlying navaid at all times.

That's part of the reason I asked the question. I have difficulty
explaining away the inconsistency between the note and the
permissiveness of the manual.

You should discuss that with Garmin. The restriction is meant to apply
to the final approach segment only. It doesn't bother me because I know
it's the same for FMS/LNAV in a 777 or a Garmin 430 in a Cessna 182.
You are using terminal mode except for the final approach segment.

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?

(Yes, I have asked Garmin the same thing, but haven't received an
answer yet.)

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.