GPS Question

unless the navigational station is the primary for the approach (which
could be true for ADF, but not DME).

Except, of course, for the famous VOR/DME OR TACAN Z RWY 15 approach at
Martin State:

http://www.naco.faa.gov/d-tpp/0602/05222VDTZ15.PDF
Are you saying that you can't use the GPS in lieu of DME for that approach?
Why not?

Yes, because the DME is the "principal instrument approach navigation
source" - that approach is a DME arc to the runway.

"Barry" wrote in message
. ..
unless the navigational station is the primary for the approach (which
could be true for ADF, but not DME).

Except, of course, for the famous VOR/DME OR TACAN Z RWY 15 approach at
Martin State:

http://www.naco.faa.gov/d-tpp/0602/05222VDTZ15.PDF
Are you saying that you can't use the GPS in lieu of DME for that
approach?
Why not?

Yes, because the DME is the "principal instrument approach navigation
source" - that approach is a DME arc to the runway.



A subtle but important observation! Have you won any bets with that one?

On Fri, 10 Mar 2006 02:10:56 GMT, "Dan Wegman"
wrote:


"Barry" wrote in message
...
unless the navigational station is the primary for the approach (which
could be true for ADF, but not DME).

Except, of course, for the famous VOR/DME OR TACAN Z RWY 15 approach at
Martin State:

http://www.naco.faa.gov/d-tpp/0602/05222VDTZ15.PDF
Are you saying that you can't use the GPS in lieu of DME for that
approach?
Why not?

Yes, because the DME is the "principal instrument approach navigation
source" - that approach is a DME arc to the runway.



A subtle but important observation! Have you won any bets with that one?

Might I ask what makes that approach any different than the ILS/DME
RWY 2 approach APOA uses as the sample in their "Use of GPS in lieu"
piece (
http://www.aopa.org/whatsnew/air_tra...u.html#figurea )
where they say "DME arcs associated with instrument approaches may be
flown using GPS distance provided the DME transmitter, on which the
arc is based, is identified in the GPS database (see Figure A)." ?

Course if we're talking about determining an alternate while planning
than yea, no substitution - but if the station is in the database and
you're shooting the approach it seems to fit the substitution rules to
me?

This article refers to the LDA/DME RWY 23 approach at EKO in Figure B.
I tried "flying" that approach on the Garmin 430 simulator and blew it
the first time because I was watching the distance readout on the
Garmin primary nav page (1st Nav page). I forgot that the unit
indicates distance to the next waypoint. After crossing the FAF, the
distance field on the nav page indicates the GPS distance to the next
waypoint (missed approach point here) rather than distance from the FAF
or the DME reference point.

What probably threw me off was that the AOPA article cautions readers
that while DME units will count DOWN to the missed approach point
(because the path is towards the DME reference point), GPS units will
count UP from the FAF. In contrast, the 430 counts DOWN to the next
waypoint (the missed approach point here). To count up from the FAF,
I'd probably have to hit OBS when approaching the FAF (though didn't
try it).

What procedure would other users of Garmin 430/530 units use with this
approach? Ideally, I'd want to see either the primary nav page or the
map page with distance shown from the DME reference point (so that I
don't have to do math in my head during the approach to calculate
distance from the FAF).

On 03/09/06 18:06, Barry wrote:
unless the navigational station is the primary for the approach (which
could be true for ADF, but not DME).

Except, of course, for the famous VOR/DME OR TACAN Z RWY 15 approach at
Martin State:

http://www.naco.faa.gov/d-tpp/0602/05222VDTZ15.PDF
Are you saying that you can't use the GPS in lieu of DME for that approach?
Why not?

Yes, because the DME is the "principal instrument approach navigation
source" - that approach is a DME arc to the runway.

Oh, right! I've never seen that before. Very cool looking approach.

I knew I was going to learn something new today :-)

Thanks for pointing it out.

Best Regards,

--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA

Yes, because the DME is the "principal instrument approach
navigation source" - that approach is a DME arc to the runway.


Sounds like pure speculation to me. Can you support with any FAA
material?

Greg Esres wrote:


Sounds like pure speculation to me. Can you support with any FAA
material?

Doesn't seem speculative to me. The FAA material is the fact that the
final approach couse is a DME ARC printed on the approach chart in bold
type. A good understanding of approach chart symbology would make that
apparent.

Also, there are the TERPS:

523. FINAL APPROACH SEGMENT. TACAN and VOR/DME final approaches may be
based either on arcs or radials. The final approach begins at a FAF and
ends at the MAP. The MAP is always marked with a fix.
a. Radial Final Approach. Criteria for the radial final approach are
specified in paragraph 513.
b. Arc Final Approach. The final approach arc shall be a continuation of
the intermediate arc. It shall be specified in NM and tenths thereof.
Arcs closer than 7 miles (15 miles for high altitude procedures) and
farther than 30 miles from the facility shall NOT be used for final
approach. No turns are permitted over the FAF.
(1) Alignment. For straight-in approaches, the final approach arc shall
pass through the runway threshold when the angle of convergence of the
runway centerline and the tangent of the arc does not exceed 15 degrees.
When the angle exceeds 15 degrees the final approach arc shall be
aligned to pass through the center of the airport and only circling
minimums shall be authorized. See Figure