GPS Question

Um, OK, I'm thick. I don't get what substitution rule I'm still
missing? With either approach you're using the VOR head for lateral
guidance and reading the distance from some fix in the GPS database
from the GPS head. Even the example approach used for how to do a DME
ARC in the KLN 94 GPS manual is an VOR/DME approach using an arc.

I guess the idea is that your position "on track" and "along track" need
differing amounts of, for lack of a better word, attention. You are
pointed along track and will cover all the along-track positions. You
want to remain on track, and not left or right of track.

For a regular VOR approach, it is the VOR that keeps you on track. DME
just reports your "along track" progress. For a DME arc it's the
reverse. You stay "on track" referring to the DME, and the VOR just
reports your "along track" progress.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

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 Fri, 10 Mar 2006 17:03:16 GMT, "Steven P. McNicoll"
wrote:


"Peter Clark" wrote in message
.. .

Um, OK, I'm thick. I don't get what substitution rule I'm still
missing? With either approach you're using the VOR head for lateral
guidance and reading the distance from some fix in the GPS database
from the GPS head. Even the example approach used for how to do a DME
ARC in the KLN 94 GPS manual is an VOR/DME approach using an arc.


But you're not using the VOR head for lateral guidance and reading the
distance from some fix in the GPS database from the GPS head with either
approach. The VOR/DME or TACAN Z RWY 15 at MTN would have you using DME
for lateral guidance and determining your position on the final approach
course from crossing VOR radials. If you substituted GPS for DME on that
approach you'd be substituting for DME where it was the principal instrument
approach navigation source.

OK, I'm not trying to be obtuse here, I'd really like to understand
what I'm doing wrong. I'm flying along using the GPS head to tell me
I'm on an arc (X) miles from (Y) transmitter, twisting the VOR head
every 10deg or so until I hit the leadin radial and then turn inbound
(or in the case of the DC approach see the runway or go missed). The
manual documents this scenario. The AOPA article seems to document
the same usage. Yet it's not allowed by the substitution rules?

"Peter Clark" wrote in message
...

OK, I'm not trying to be obtuse here, I'd really like to understand
what I'm doing wrong. I'm flying along using the GPS head to tell me
I'm on an arc (X) miles from (Y) transmitter, twisting the VOR head
every 10deg or so until I hit the leadin radial and then turn inbound
(or in the case of the DC approach see the runway or go missed). The
manual documents this scenario. The AOPA article seems to document
the same usage. Yet it's not allowed by the substitution rules?


AIM para 1-1-19.f.1.(b)(6):

"Charted requirements for ADF and/or DME can be met using the GPS system,
except for use as the principal instrument approach navigation source.

What serves as the principal instrument approach navigation source for the
ILS/DME RWY 2 at DRO? What serves as the principal instrument approach
navigation source for the VOR/DME RWY 15 at MTN?

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?

On Sat, 11 Mar 2006 04:12:16 GMT, "Steven P. McNicoll"
wrote:


"Peter Clark" wrote in message
.. .

OK, I'm not trying to be obtuse here, I'd really like to understand
what I'm doing wrong. I'm flying along using the GPS head to tell me
I'm on an arc (X) miles from (Y) transmitter, twisting the VOR head
every 10deg or so until I hit the leadin radial and then turn inbound
(or in the case of the DC approach see the runway or go missed). The
manual documents this scenario. The AOPA article seems to document
the same usage. Yet it's not allowed by the substitution rules?


AIM para 1-1-19.f.1.(b)(6):

"Charted requirements for ADF and/or DME can be met using the GPS system,
except for use as the principal instrument approach navigation source.

What serves as the principal instrument approach navigation source for the
ILS/DME RWY 2 at DRO? What serves as the principal instrument approach
navigation source for the VOR/DME RWY 15 at MTN?

OK, using that as a baseline then GPS wouldn't be a permissible
substitute for DME in any approach using a DME arc, so why would it be
documented in the manuals if it's not permissible?

"Peter Clark" wrote in message
...

AIM para 1-1-19.f.1.(b)(6):

"Charted requirements for ADF and/or DME can be met using the GPS system,
except for use as the principal instrument approach navigation source.

What serves as the principal instrument approach navigation source for the
ILS/DME RWY 2 at DRO? What serves as the principal instrument approach
navigation source for the VOR/DME RWY 15 at MTN?


OK, using that as a baseline then GPS wouldn't be a permissible
substitute for DME in any approach using a DME arc, so why would it be
documented in the manuals if it's not permissible?


You didn't answer the questions. We can proceed only after you answer the
questions.

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

On Sat, 11 Mar 2006 20:17:46 GMT, "Steven P. McNicoll"
wrote:


"Peter Clark" wrote in message
.. .

AIM para 1-1-19.f.1.(b)(6):

"Charted requirements for ADF and/or DME can be met using the GPS system,
except for use as the principal instrument approach navigation source.

What serves as the principal instrument approach navigation source for the
ILS/DME RWY 2 at DRO? What serves as the principal instrument approach
navigation source for the VOR/DME RWY 15 at MTN?


OK, using that as a baseline then GPS wouldn't be a permissible
substitute for DME in any approach using a DME arc, so why would it be
documented in the manuals if it's not permissible?


You didn't answer the questions. We can proceed only after you answer the
questions.

OK. I believe the answer is the GS/localizer and VOR respectively.

"Peter Clark" wrote in message
...

OK. I believe the answer is the GS/localizer and VOR respectively.


Why did you choose VOR for the VOR/DME RWY 15 at MTN? Do you see VOR
serving the same role there as the localizer does for the ILS/DME RWY 2 at
DRO?