revisiting DME vs. GPS slant range
Mike Weller
I did the unthinkable on a newsgroup like this. Remembering some
"opinions" a week or so ago about altitude and GPS, I decided to
actually fly a test.
I flew over a VORTAC at 11,500 feet. Twice. Once with a Garmin 430.
The second time with a Garmin 195. On both, the distance to station
ran down to zero as I crossed it. I was looking at the witch's hat as
I flew over.
So to all of you who believe that GPS somehow gives slant range like a
DME, well, if your's does, then give the model number and location. I
don't believe you! Further, if they can't show an accurate distance
to waypoint, what good are they?
This one was done at the Rocket VORTAC (RQZ), 112.2 at about 11,500
feet, or about two miles above the VORTAC.
I can't see anything about the -430 that requires an altitude input
for IFR approaches. It is one sweet little machine.
Mike Weller
Oh, the GPS altitude agreed within 200 feet of the barometric altitude
on both receivers (sorry about the fluttering heart that will cause
some here who are contributors, but not pilots).
Tarver Engineering
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
news:3d78221c....@news-east.onlynews.com...
GPS tends to be withing 300 feet of sea level, but that is a function of the
Earth's actual shape compared to the WGS-84 model. (see RTCA DO-208 change
2)
John
Nick
> for IFR approaches. It is one sweet little machine.
That's why they call it the blind altitude encoder <grin>. It's hooked to
both your Garmin and the transponder and is required for RAIM. It's also
used for the VNAV page.
> Oh, the GPS altitude agreed within 200 feet of the barometric altitude
> on both receivers (sorry about the fluttering heart that will cause
> some here who are contributors, but not pilots).
>
It's a lot better since SA has been turned off.
BH
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
news:3d78221c....@news-east.onlynews.com...
>
I was wrong on this.
I also flew a test last week and concur with Mike - GPS does not give the
slant range. When you think about it, the GPS is calculating the great
circel distance between two lat/longs. Duh.
Regards,
Newps
approach chart is the same as what's seen on the GPS.
Roy Smith
> So to all of you who believe that GPS somehow gives slant range like a
> DME, well, if your's does, then give the model number and location. I
> don't believe you! Further, if they can't show an accurate distance
> to waypoint, what good are they?
I don't believe them either.
To calculate slant range, you need to know the elevation of the fix
you're navigating to. While it's certainly reasonable to have
elevations of navaids and airports in the database, it's less likely
to have elevations of intersections and virtually impossible that it's
got the full terrain map it would need to compute the elevation of any
arbitrary lat/long fix.
Besides, slant range is a problem with DME which couldn't be worked
around given the technology of the time. Why would anybody go to the
effort to simulate it when we can do better now? Perhaps if you've
got a strikefinder tied into your moving-map GPS, it should use
information about detected lightning strikes to "fine-tune" the
displayed bearing to NDB stations? Perhaps autopilots should
introduce random heading changes to simulate the familiar hand-flown
wavering of the CDI as we track a localizer?
Ron Natalie
"Tarver Engineering" <jta...@sti.net> wrote in message news:3d78...@news.sierratel.com...
> GPS tends to be withing 300 feet of sea level, but that is a function of the
> Earth's actual shape compared to the WGS-84 model. (see RTCA DO-208 change
> 2)
That and the accuracy of the GPS for the current satellite gemoetry. Vertical accuracy
goes to hell alot faster than horizontal.
C J Campbell
enough to believe that GPS gives slant range.
It is very easily demonstrated on any plane equipped with both DME and GPS.
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
news:3d78221c....@news-east.onlynews.com...
|
Mike Weller
>Now go to charted points on an approach and see if the DME on the
>approach chart is the same as what's seen on the GPS.
>
Danged if I can tell. At 2.5 nm DME (i.e. slant range) and at an
altitude of 2000 feet above the VORTAC, the difference between the DME
and the ground distance from the station is 133 feet or 0.022 nm.
This assumes a normal step down at 2.5 DME, what I would call a
representative approach number. At distances closer than this, you'll
be using station passage as the fix, not distance. So if I use the GPS
number instead of the slant range, I'll start my descent 133 feet too
late. The farther from the station I get, the less the difference.
At 5 DME it is less than 100 feet.
At a 90 kt approach speed, I'm traveling at 150 feet per second. So
the difference really works out to less than a one second response
time.
I would love to have you give me an example of any approach where the
distiction you seem to be making is even measurable from what you see
on your radar scope, or in an aircraft, using GPS instead of DME slant
range.
Mike Weller
Tarver Engineering
"Ron Natalie" <r...@sensor.com> wrote in message
news:d%2e9.35446$%M3.2...@atlpnn01.usenetserver.com...> > GPS tends to be within 300 feet of sea level, but that is a function of
the
> > Earth's actual shape compared to the WGS-84 model. (see RTCA DO-208
change
> > 2)
>
> That and the accuracy of the GPS for the current satellite gemoetry.
Vertical accuracy
> goes to hell alot faster than horizontal.
The offset from real Earth is an important reason why WAAS is hosed.
John
I Lee Hetherington
> This assumes a normal step down at 2.5 DME, what I would call a
> representative approach number. At distances closer than this, you'll
> be using station passage as the fix, not distance. So if I use the GPS
> number instead of the slant range, I'll start my descent 133 feet too
> late.
You'll start your descent too early because the GPS distance will be less
than the DME slant range.
--Lee
Ron Natalie
"Tarver Engineering" <jta...@sti.net> wrote in message news:3d78dff1$1...@news.sierratel.com...
> The offset from real Earth is an important reason why WAAS is hosed.
>
C'mon, WAAS is hosed long before you get to geometrical issues :-)
Ron Natalie
"I Lee Hetherington" <i...@sls.lcs.mit.edu> wrote in message news:3D78EE82...@sls.lcs.mit.edu...
Well, it depends whether you're going to or from the DME.
Tarver Engineering
OK, you got me there, but even if all the rest had worked, the geometry
would have still prevented sole means. Congress is still dumping money down
this rathole, with FAA knowing full well WAAS can never work; with L5 having
an identical flaw. For what has been spent already we could have CAT III
LAAS everywhere.
John
Mike Weller
wrote:
First off, I like reading this newsgroup. There's a lot of good stuff
here. I like to review the basics. However, some things that just
didn't seem to pass the common sense truth test were written (is that
an understatement about usenet in general?). I really didn't know
"FOR SURE" what the GPS would read when tracking to a DME station. So
I didn't write anything. A veritable plethora of others did. And in
all honesty, I don't really mind that, in the context of informal
chat. What does piss me off is when someone asserts that something is
a fact, just because they say so. I like clear, complete
explainations, preferably concise and verifiable.
I was thinking about a normal approach where you stepped down after
VOR/DME passage. So, since the Hypotenuse (slant range) is longer
than the outbound ground distance (I know, I'm assuming a flat earth,
give me a break) when your GPS reads 2.5 nm, you're 133 feet past the
2.5 nm point that you read from the DME.
Further, the only approaches where you step down within 2.5 nm INBOUND
to the DME (at least that I've seen, or can rationalize) the DME is
located on the field (pretty common) so at that distance you would
already be much lower on the approach and the difference between slant
range and GPS would be even smaller. Regardless, if you're going to
step down 2000 feet in 2.5 nm at 90 kts. you're going to be descending
at 1333 feet per minute. At 150 kts, it's a cool 2000 fpm. Aspen,
Colorado on an mls approach maybe? I don't know.
Mike Weller
I Lee Hetherington
station was ahead of you. Never mind.
--Lee
Mike Weller
Lee,
I know that I used that phrase, but it was not directed at you. Your
contribution was correct, in that I hadn't really specified a
direction.
Rather, my comment was directed at some who cannot resist responding
to questions, even though they don't have a clear understanding of the
problem. This seems to be particularly abundant in questions
involving FARs.
Mike Weller
James Cummiskey
approach requiring DME to figure out where the fixes are? I'm assuming that
all DME distances on IAPs are based on slant range, correct?
Regards, Jim
"C J Campbell" <christoph...@NOSPAMhotmail.com> wrote in message
news:unhh6an...@corp.supernews.com...
ArtP
<jccu...@yahoo.com> wrote:
>So, the question is now: Can I legally use GPS as a "pseudo-DME" on an
>approach requiring DME to figure out where the fixes are? I'm assuming that
>all DME distances on IAPs are based on slant range, correct?
If the GPS is IFR certified, the database is current, and the DME
navid is in the database the answer is yes. You can also use the GPS
even if the DME navid is not in the database as long as another fix
(such as the IAF) is in the database and the chart shows the distance
from that fix to the fix you are looking for.
Mike Weller
<christoph...@NOSPAMhotmail.com> wrote:
>It is very easily demonstrated on any plane equipped with both DME and GPS.
>
Not on a published approach. Please cite an example.
Mike Weller
Defly
>approach requiring DME to figure out where the fixes are? I'm assuming that
>all DME distances on IAPs are based on slant range, correct?
2 questions here - can you use GPS as a pseudo DME? I think you probably
could. I'm a salesman not a mathematician, but my thought is that at the low
AGL altitudes we're likely talking about here the slant range component of the
DME distance isn't appreciable enough to make a big difference. Legally? I
don't even want to enter the den of flamers on that issue. Interesting thread
- I'm just thinking out loud here.
Cheers
Drew
Tarver Engineering
"Defly" <de...@aol.com> wrote in message
news:20020908114902...@mb-bg.aol.com...
> >So, the question is now: Can I legally use GPS as a "pseudo-DME" on an
> >approach requiring DME to figure out where the fixes are? I'm assuming
that
> >all DME distances on IAPs are based on slant range, correct?
>
> 2 questions here - can you use GPS as a pseudo DME?
Yes.
GPS is certified as Long Range Nav and not DME; so any slant range comming
out of a GPS is a violation of the basis for certification.
John
Larry Fransson
de...@aol.com (Defly) wrote:
> can you use GPS as a pseudo DME?
Yes. The FAA said so some time ago.
--
Larry Fransson
Seattle, WA
Dan Thompson
IOW, when it reports 27.2 mi. from ABC vor, is that GPS-derived or does it
have DME?
Tarver Engineering
"Dan Thompson" <dt...@NOSPAMswbell.net> wrote in message
news:rPKe9.9236$4_1.199...@newssvr30.news.prodigy.com...
> Just out of curiosity, does a GPS-NAV like a Garmin 430/530 have DME in
it?
No, a GPS is certified as Long Range Nav, not DME.
> IOW, when it reports 27.2 mi. from ABC vor, is that GPS-derived or does it
> have DME?
No DME in GPS; and any indication of DME like behavior is grounds for an AD.
John
Roy Smith
It's purely a calculated distance based on the GPS signal.
That's not to say that you couldn't build a GPS-based nav system with
integrated DME, but to the best of my knowledge, none of the
commercially available systems (certainly not those being sold to the GA
market) do that.
Robert Moore
> an AD.
AIM 1-1-21. Global Positioning System (GPS)
5. Subject to the restrictions below, operators in the U.S. NAS
are authorized to use GPS equipment certified for IFR operations
in place of ADF and/or DME equipment for en route and terminal
operations. For some operations there is no requirement for the
aircraft to be equipped with an ADF or DME receiver, see
subparagraphs f6(g) and (h) below. The ground-based NDB or DME
facility may be temporarily out of service during these operations.
Charting will not change to support these operations.
(a) Determining the aircraft position over a DME fix. GPS satisfies
the 14 CFR Section 91.205(e) requirement for DME at and above 24,000
feet mean sea level (MSL) (FL 240).
(b) Flying a DME arc.
And so-on....................................
Bob Moore
Mike Weller
That's pretty funny. The first DME I ever used had a needle on the
miles indicator that looked like a speedometer in a car. The needle
was about 1 inch tall and had an arc of about 120 degrees that read
from zero to one hundred ( I forget the top end, it might have been
more or less). The difference between 27.2 nm and 27.1 nm DME would
have been less than the width of a short hair.
To answer your question, no, the 430 does not have a DME receiver. It
also doesn't have an ADF. What it does have is a fully functional
VOR/LOC/Glideslope receiver. It's the pilot's choice of whether to
use the reciever data, or the GPS, or both. That is a bug, in my
mind, because it does make you think a little bit more. However, it
will do everthing but physically slap you on the wrist pleading with
you to select, and adhere to the best navigational guidance source.
I've never flown a 530, but I would imagine that it is similar.
The difference between a KNS-89, et. al. and the newer stuff is night
and day. There are other, older, IFR GPSs that I've flown with, and
they all suffer from the same problem, lack of an intuitive user
interface. The one thing that they all do the best is give you an
immediate go-to for your next waypoint, and with that a range and time
to it. What would DME add to that?
It's no wonder we aren't sure of whether or not the GPS is giving
slant range. First of all, it doesn't matter. Secondly, the workload
to get a GPS set up for an approach is pretty high, compared to the
classic VOR/LOC/DME/ILS/NDB that we're used to flying. The airlines
have struggled with that for years, getting their FMS systems to work
"easily". The American Cali tragedy was a result of mismanagement of
the FMS. So, for a third reason, I still feel comfortable getting
"raw data" by triangulation and tracking and manual timing using the
old skills.
Sorry for rambling, but I've learned a lot of practical things from
this thread.
Mike Weller
Sydney D. Hoeltzli
> So, the question is now: Can I legally use GPS as a "pseudo-DME" on an
> approach requiring DME to figure out where the fixes are? I'm assuming that
> all DME distances on IAPs are based on slant range, correct?
The answer to your question is: yes, you can legally use an IFR
enroute and terminal certified (or better) GPS to substitute for
DME *providing* the navaid from which the DME distance is derived,
is part of your GPS database. IFR GPS can also be used as a
substitute for ADF in an approach annotated "ADF required" (but
not an NDB approach w/out GPS overlay AFAIK), again provided
the NDB is part of your GPS database.
ie VOR/DME approach, VOR can be found in your IFR GPS database =
good to go Loc/BC annotated "ADF required" to identify MAHP =
good to go.
ILS/DME approach, localizer is NOT found in your IFR GPS database,
DME is based on loc, NOT ok, you can't just enter the loc coordinates
and go for it (legally).
The regulatory basis for this is a NOTAM published July 16th 1998
and annotated 6/25/98(ATA-100) at the bottom; I apologize if this
is not sufficient to allow you to find it, but my copy was FAXed to
me by the local FSDO and I'm sure AOPA or your FSDO can help you
out.
If you have a VFR GPS, you can not legally use it to substitute
for installed DME or ADF on IAPs. Practically of course....
Parenthetically, I note that the regulatory basis authorizing our
GPS for use in approaches is the FAA approved flight manual supplement,
which for our mfr (Apollo) requires that "the approach data" rather
than the approach database, be current. IOW if the current approach
plate indicates that the approach was last revised 2 years ago
and my database is more recent than that, I'm good to go. Wahoo.
In contrast, the above notam requires that the approach *database*
be current.
Therefore, legally speaking, I can go out and shoot a GPS approach
which has been in existance for 1 yr with a 6 month old database,
but I can't (legally) fly an ILS approach on which I'll use the ADF
(which has been there since I was a gleam in mommy's eye) only to
identify the MAHP in the (unlikely) event that 1) I go missed AND
2) I havent been issued different MA instructions by ATC.
Go figgur.
Cheers,
Sydney
Sydney D. Hoeltzli
> If the GPS is IFR certified, the database is current, and the DME
> navid is in the database the answer is yes. You can also use the GPS
> even if the DME navid is not in the database as long as another fix
> (such as the IAF) is in the database and the chart shows the distance
> from that fix to the fix you are looking for.
Art,
Interesting. Can you provide the regulatory basis for this latter?
It was not in the original NOTAM which allowed DME/ADF
Perhaps there is something more recent and we were snoozing :)
Sydney
ArtP
If you mean specifically the distance from a fix (1-21-1 (f) (7))
Tarver Engineering
"Robert Moore" <rmoo...@tampabay.rr.com> wrote in message
news:Xns928387B18F8B3rm...@65.32.1.6...
Slant range reported from a GPS is an automatic Airworthyness Directive and
possible cancellation of all the Manufacturer's 21.303 Authority. Although
GPS may be substituted for DME, it is certified as LRN and has no basis of
certification as DME.
John
>
> (b) Flying a DME arc.
>
> And so-on....................................
>
> Bob Moore
Geeze, I should have known it was Bob plumbing this dog shit.
Sydney D. Hoeltzli
> If you mean specifically the distance from a fix (1-21-1 (f) (7))
I mean specifically the distance from a fix, and specifically
the *regulatory basis*.
The AIM is not regulatory. The regulatory basis for most
IFR GPS operations is the "approved flight manual supplement"
incorporated into the plane's flight manual by the form 337
approving the installation. (as I understand it)
The regulatory basis for using GPS as a DME or ADF substitute
is the '98 NOTAM I mentioned in another post. If there is another
regulatory basis, I'd like to know about it!
This NOTAM does not specify that one can use GPS to determine the
DME distance from a navaid not in the database if its distance
from a different navaid (in the database) is charted.
This would seem to allow use of GPS to, for example, fly an ILS/DME
approach *if* the DME distances from another navaid (the LOM for
example) are charted.
However, I'd like to know the regulatory basis since the AIM is
not regulatory. I know the regulatory basis for the rest of the
GPS stuff in the AIM.
Cheers,
Sydney
ArtP
<hoel...@swbell.net> wrote:
>The AIM is not regulatory.
The following quote from the AIM is enough for me to feel that
following the guidelines in the AIM will insure that I am in
compliance with FAA rules. You might argue that I don't have to do
what it says but you will have a hard time making a case that if I do
what it says I am in violation of FAA regulations.
d. This publication, while not regulatory, provides information which
reflects examples of operating techniques and procedures which may be
requirements in other federal publications or regulations. It is made
available solely to assist pilots in executing their responsibilities
required by other publications.
>The regulatory basis for most
>IFR GPS operations is the "approved flight manual supplement"
>incorporated into the plane's flight manual by the form 337
>approving the installation. (as I understand it)
If you are looking for justification based on a piece of hardware then
study the GNS430 stored procedures and the GNS430 POH (which according
to my POH governs the use of the GNS430 and must readily accessible to
the pilot in flight). You will find that some step down fixes are not
present and must be measured from the following fix (distance provided
by the approach procedure) since DME distances are not available while
executing the procedure.
Rich Hare
saw the signature in time and realized I didn't really have to, considering who
wrote it.
Don't tell John about my post. I'm sure I'm in his killfile.
Rich
H Pylori
"Rich Ahrens" <r...@visi.com> wrote in message
news:3D7CC5FE...@visi.com...
> More coddling from rec.aviation.ifr...
>
> Rich Hare wrote:
> > I was really struggling to understand what was written below
Rich joins the club. We all have our sea stories of trying to decipher the
incoherent ramblings of Tarver.
In the end, we discover that Tarver probably deliberately obfuscates and
talks in circles because he loves the attention he gets. By carefully
rearranging the truth details, he can then work weeks of churn by asserting
that if *you* knew more, you'd have *understood* in the first place. This
is the Tarver way. A rather highly developed troll, actually, and certainly
effective. The sad little man has made himself the center of attention in
several newsgroups with this scheme. You have to tip your hat to the guy.
Defly
>
>> Slant range reported from a GPS is an automatic Airworthyness Directive and
>> possible cancellation of all the Manufacturer's 21.303 Authority. Although
>> GPS may be substituted for DME, it is certified as LRN and has no basis of
>> certification as DME.
>>
>> John
How exactly would one EVER see "slant range reported from a GPS..." ? Slant
range distance is the length of the side of a triangle where the other two
sides are (a) the horizontal distance over the ground from the DME station to a
point directly under the aircraft and (b) the altitude of the aircraft above
the DME station. Since GPS gives position solely as a calculated position on
the ground I fail to see how slant range could ever be shown by a GPS. Now
remember - I'm a salesman and not a mathematician or an engineer (I am certain
John is an engineer because his spelling is so atrocious) I'm just trying to
understand the concept he is purporting as truth. Or is this just another
example of misinformation being worse than no information at all?
Cheers
Drew
Ron Natalie
"Defly" <de...@aol.com> wrote in message news:20020909135443...@mb-fp.aol.com...
>
> How exactly would one EVER see "slant range reported from a GPS..." ? Slant
> range distance is the length of the side of a triangle where the other two
> sides are (a) the horizontal distance over the ground from the DME station to a
> point directly under the aircraft and (b) the altitude of the aircraft above
> the DME station.
Well actually, it's the straight line distance between the airplane and the station.
> Since GPS gives position solely as a calculated position on
> the ground I fail to see how slant range could ever be shown by a GPS.
Well, the above statement is false. GPS generates a position in space. The only
thing missing is the position of the DME in space. Now the problem most likely
is that currently the only thing the GPS's database has is the 2D (i.e. referenced
to the elipsoid) location of the DME. However, if it knew it's elevation, it could
compute slant range (if that were at all useful).
Of course, you would somehow indicate to the GPS that you really wanted slant
range rather than the horizontal distance to the station.
Defly
horizontal distance
Tarver Engineering
> >
> >> Slant range reported from a GPS is an automatic Airworthyness Directive
and
> >> possible cancellation of all the Manufacturer's 21.303 Authority.
Although
> >> GPS may be substituted for DME, it is certified as LRN and has no basis
of
> >> certification as DME.
> How exactly would one EVER see "slant range reported from a GPS..." ?
Some posters to this thread seem to believe slant range is derived from the
c-85 altitude intput to their GPS. Did you read the title of this thread?
> Slant
> range distance is the length of the side of a triangle where the other two
> sides are (a) the horizontal distance over the ground from the DME station
to a
> point directly under the aircraft and (b) the altitude of the aircraft
above
> the DME station. Since GPS gives position solely as a calculated position
on
> the ground I fail to see how slant range could ever be shown by a GPS.
I agree.
> Now
> remember - I'm a salesman and not a mathematician or an engineer (I am
certain
> John is an engineer because his spelling is so atrocious) I'm just trying
to
> understand the concept he is purporting as truth. Or is this just another
> example of misinformation being worse than no information at all?
I am writing that the title of this thread, and those promoting the notion
of GPS slant range, are probably wrong. If on the other hand, their
certified GPS is reporting slant range, then the FAA must remove the
certification. There is no certification basis upon which GPS slant range
can exist, as GPS is certified as a LRN.
John
Tarver Engineering
> My mistake - it's not the horizontal distance over the ground it's just
the
> horizontal distance
Now go explain that to Rich Hare.
John
Pooh Bear
Bizarrely enough, I think I got the meaning on the second reading. Does this
mean I have mastered 'Tarverese' ?
Should I see a doctor ?
Graham
--
remove the obvious to email
H Pylori
"Pooh Bear" <rabbitsfriend...@notsohotmail.com> wrote in message
news:3D7CEB96...@notsohotmail.com...
Exorcist.
C J Campbell
"Dan Thompson" <dt...@NOSPAMswbell.net> wrote in message
news:rPKe9.9236$4_1.199...@newssvr30.news.prodigy.com...
The Garmin units do not have DME; they use GPS to derive distance. They
receive VORs normally. They do not include an ADF in the package. However,
since you can use GPS in place of DME and ADF all you really need are the
VORs anyway.
These are great units, BTW, but they require adequate training to use. I
have seen people bust Instrument check rides because they did not know how
to dial in a localizer on the unit.
C J Campbell
does not give slant range. However, at the distance and altitude that DME
arcs are flown the difference is very small - smaller than most pilots can
fly.
GPS can be used as a substitute for DME and/or ADF, but it does not become a
DME or ADF when you do that.
"H Pylori" <ppgo...@rocketmail.com> wrote in message
news:alii4c$pc7$0...@pita.alt.net...
C J Campbell
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
news:3d7aa116....@news-east.onlynews.com...
| On Fri, 6 Sep 2002 08:06:55 -0700, "C J Campbell"
| <christoph...@NOSPAMhotmail.com> wrote:
|
| >It is very easily demonstrated on any plane equipped with both DME and
GPS.
| >
|
| Not on a published approach. Please cite an example.
|
| Mike Weller
|
|
I am not sure I understand what you want. However, if you compare a GPS
distance with a DME range you will find a slight difference that will become
greater as you get nearer the fix. There is nothing magical about published
approaches that changes the laws of physics.
Tarver Engineering
"C J Campbell" <christoph...@NOSPAMhotmail.com> wrote in message
news:unqm26n...@corp.supernews.com...
> What Tarver is trying to say is that GPS is not the same as DME and that
GPS
> does not give slant range. However, at the distance and altitude that DME
> arcs are flown the difference is very small - smaller than most pilots can
> fly.
You really ought to ignore the cross posts from the Poultry Club.
John
H Pylori
"Tarver Engineering" <jta...@sti.net> wrote in message
news:3d7d...@news.sierratel.com...
Sure, John. Campbell posted a coherent thought, whereas this jumble of
words
was attributed to you. If this was not written by you then some asshole is
posting under your name:
Mike Weller
<christoph...@NOSPAMhotmail.com> wrote:
>I am not sure I understand what you want.
O.K. What I want you (or anyone else for that matter) is to show me
an example of a published fix, using DME, where it would be measurably
different from using GPS for the same fix. My point is that they are,
within reason, the same.
You also wrote:
>However, if you compare a GPS
>distance with a DME range you will find a slight difference that will become
>greater as you get nearer the fix. There is nothing magical about published
>approaches that changes the laws of physics.
>
Cute. Very cute. It still doesn't seem to make your point, whatever
that is.
By the way, what is your point? That DME slant range is not the same
as GPS ground distance. Well, you're a little late stepping up the
plate on that one, sport.
Is it that somehow, a pilot needs to be extra observant when using GPS
range instead of an honest to goodness DME while on a DME approach?
If so, show an example of an approach were it would make a measurable
difference.
Mike Weller
Limey Dave
Scott Aron Bloom
distance to waypoint
on approach is EASY to find.
Try the loc 17 approach in to UAO (sorry I use AOPA for my NOAA charts)
http://download.aopa.org/iap/20020808/nw1of1/uao_loc_rwy_17.pdf
The GPS waypoint for the missed is the RW17 which is 1 mile from the DME
transmitter.
Hence, when you are doing this LOC approach with the GPS as a DME, your GPS
will go
down to 0, yet a DME will say 1.0.
When ever I fly an approach using my GPS as a DME, I will write in the GPS
value before I fly
the approach for all DME waypoints.
Scott
CFI-I
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
news:3d7d6a5a...@news-east.onlynews.com...
Craig Prouse
> An example of where DME distance is significantly different from GPS
> distance to waypoint
> on approach is EASY to find.
>
> Try the loc 17 approach in to UAO (sorry I use AOPA for my NOAA charts)
> http://download.aopa.org/iap/20020808/nw1of1/uao_loc_rwy_17.pdf
>
> The GPS waypoint for the missed is the RW17 which is 1 mile from the DME
> transmitter.
>
> Hence, when you are doing this LOC approach with the GPS as a DME, your GPS
> will go
> down to 0, yet a DME will say 1.0.
Advisory circular guidance on the substitution of GPS for DME recommends
that you configure your GPS to show distance to the I-UAO fix.
The missed approach point (RW17) is 1.0 miles from the I-UAO fix, which is
in your database. When you're at the missed approach point, your DME will
read 1.0 and your GPS should read 1.0 miles from I-UAO. The point is that
there is no discernable difference when your active waypoint is the DME
station of interest. If you choose to navigate relative to a different GPS
waypoint than the DME station in question, any discrepancy is one of your
own making, not an inconsistency between the two types of equipment.
Approaches like UAO LOC RWY 17 do not have an approved GPS overlay. Some
GPS manufacturers have created virtual overlays to facilitate approach
monitoring, but in the process they have introduced inconsistencies between
the representation on the approach plate and the representation in the
approach database. My GPS doesn't even contain this approach or the RW17
waypoint. Caveat emptor.
Dave Butler
>
> An example of where DME distance is significantly different from GPS
> distance to waypoint
> on approach is EASY to find.
>
> Try the loc 17 approach in to UAO (sorry I use AOPA for my NOAA charts)
> http://download.aopa.org/iap/20020808/nw1of1/uao_loc_rwy_17.pdf
>
> The GPS waypoint for the missed is the RW17 which is 1 mile from the DME
> transmitter.
>
> Hence, when you are doing this LOC approach with the GPS as a DME, your GPS
> will go
> down to 0, yet a DME will say 1.0.
I'm not following this. The localizer DME antenna is in your
GPS database and should be the active waypoint. When you are
1 mile from it, that's your missed approach point, whether
you are using DME or GPS.
Dave
Mike Weller
<sc...@sabgroup.com> wrote:
>An example of where DME distance is significantly different from GPS
>distance to waypoint
>on approach is EASY to find.
>
>Try the loc 17 approach in to UAO (sorry I use AOPA for my NOAA charts)
>http://download.aopa.org/iap/20020808/nw1of1/uao_loc_rwy_17.pdf
>
>The GPS waypoint for the missed is the RW17 which is 1 mile from the DME
>transmitter.
>
No it's not. The MAP is 1 nm (DME slant range) from I-UOC. Where
your DME reads 1.0000000 nm at 580 feet above the DME, your GPS will
read 0.995 nm ground range to the DME. So at the MAP, that's a
difference of 28 feet. How long is your airplane?
Take a look at the approach again. You have two ways to fly it. One
is to use timing from LUTZZ. The other is to use DME.
What is interesting to me is whether or not an ARINC derived database
(which they all are) will even show a localizer as a waypoint. I
don't think it will (and I'm leaving myself out on a limb here). You
can certainly enter it manually, just like you're doing with using the
runway end point, but it's not part of the published approach.
Thanks, I'll do a test tomorrow. I like stuff like this.
Mike Weller
Craig Prouse
> What is interesting to me is whether or not an ARINC derived database
> (which they all are) will even show a localizer as a waypoint. I
> don't think it will (and I'm leaving myself out on a limb here). You
> can certainly enter it manually, just like you're doing with using the
> runway end point, but it's not part of the published approach.
Localizers with DME are waypoints in the IFR GPS databases. This was a big
deal a couple of years ago when they were added because it allows one to
substitute GPS for DME properly on approaches just like UAO LOC RWY 17.
Obviously if the GPS is measuring the distance to some other point than the
DME station, the numbers aren't going to match the ones on the approach
plate. This has nothing to do with slant range.
C J Campbell
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
| On Mon, 9 Sep 2002 19:29:02 -0700, "C J Campbell"
| <christoph...@NOSPAMhotmail.com> wrote:
|
| >I am not sure I understand what you want.
|
| O.K. What I want you (or anyone else for that matter) is to show me
| an example of a published fix, using DME, where it would be measurably
| different from using GPS for the same fix. My point is that they are,
| within reason, the same.
|
| You also wrote:
|
| >However, if you compare a GPS
| >distance with a DME range you will find a slight difference that will
become
| >greater as you get nearer the fix. There is nothing magical about
published
| >approaches that changes the laws of physics.
| >
|
| Cute. Very cute. It still doesn't seem to make your point, whatever
| that is.
|
| By the way, what is your point?
My point is that while GPS distance is different than slant range, it rarely
makes enough of a difference when flying a DME arc to be worth worrying
about.
If you are saying that they are the same for most practical purposes, I
would agree with you. If you are claiming that they are the same thing,
though, I would say that you are probably incorrect.
Mike Weller
<christoph...@NOSPAMhotmail.com> wrote:
>If you are saying that they are the same for most practical purposes, I
>would agree with you. If you are claiming that they are the same thing,
>though, I would say that you are probably incorrect.
>
Hello Chris,
Ok, I'm now saying, "They are the same for most practical purposes".
Further, although I never said that they were the same thing, I've
found that there are some big differences in the way they are used.
Scott Aron Bloom pointed out the LOC RWY 17 approach to the UAO
airport. At first glance, DME and the GPS overlay should coincide
within 28 feet at the MAP. So I took the time to set up the approach
on a Garmin-430. When the approach was input, I got the message "Not
approved for GPS" and "GPS is for monitoring only." "Danger Will
Robinson". Using DME, the MAP is 1.0 nm from the I-UAO localizer/DME.
Guess where the MAP is for the overlayed GPS approach. At the RW17
"waypoint" (the approach end of 17). As the DME counts down to 1.0,
the GPS counts down to 0.0 for the MAP. I would have thought that the
GPS would overlay exactly with the LOC RWY 17. In fact, the I-UAO/DME
"intersection" doen't even show up on the GPS overlay. You can
monitor the DME distance on the GPS by selecting go-to the I-UOC
localizer. In that case, your DME readout would be "practically" the
same.
As far as finding the I-UAO localizer/DME, on my -195 it doesn't show
up in the database (mine is current). Therefore I extrapolated that
the thing was not in the ARINC database. I was wrong. It does show
up on the -430. Further, as far as I can tell, there is no requirement
that the localizer transmitter and the associated DME transponder are
even at the same location. It's just a matter of frequency pairing
(i.e. the DME channel that is automatically selected when you tune the
localizer frequency).
So, thanks also to Craig Prouse for setting me straight on this.
Mike Weller
Scott Aron Bloom
distance
to the MAP (0.0 not 1.0) which is the RW17. if someone knows of a way
to have it read the other distance (distance to the DME) when in "Support of
an approach mode".
Ie, not a GPS approach, not an overlay approach, a LOC approach with
optional DME componenent,
where the GPS is only acting as a DME, please let me know.
Scott
"Craig Prouse" <cra...@apple.com> wrote in message
news:B9A4F764.65F15%cra...@apple.com...
Mike Weller
<sc...@sabgroup.com> wrote:
>I have flown this approach numerous times, and the 430, always reports
>distance
>to the MAP (0.0 not 1.0) which is the RW17. if someone knows of a way
>to have it read the other distance (distance to the DME) when in "Support of
>an approach mode".
>
>Ie, not a GPS approach, not an overlay approach, a LOC approach with
>optional DME componenent,
>where the GPS is only acting as a DME, please let me know.
>
>Scott
Scott, you are correct. For more details see my reply to C.J.
Campbell.
Mike Weller
Mike Weller
Weller) wrote:
> You can
>monitor the DME distance on the GPS by selecting go-to the I-UOC
>localizer. In that case, your DME readout would be "practically" the
>same.
>
Duh, the I-UAO localizer. I can't read my own notes.
Mike Weller
Roger Halstead
"Mike Weller" <mid...@NOSPAMmindspring.com> wrote in message
> On Wed, 11 Sep 2002 21:51:54 -0700, "C J Campbell"
> <christoph...@NOSPAMhotmail.com> wrote:
> As far as finding the I-UAO localizer/DME, on my -195 it doesn't show
> up in the database (mine is current).
Those fixes do show up on the 295 and probably the 196.
Mine is set up for WAAS as well. It has all the fixes for both VOR
approaches including the missed and holds. Both have "two" IAFs, depending
ont eh direction of entry.
> Therefore I extrapolated that
> the thing was not in the ARINC database. I was wrong. It does show
> up on the -430. Further, as far as I can tell, there is no requirement
> that the localizer transmitter and the associated DME transponder are
> even at the same location. It's just a matter of frequency pairing
> (i.e. the DME channel that is automatically selected when you tune the
> localizer frequency).
Not necessiarily. They may not even be related to each other.
When flying the ILS at MBS, (I have RNAV), I tune the VOR...read the DME,
select the <hold> button and then switch to the localizer/ILS. If I only
use the ILS there is no DME showing.
--
Roger Halstead (K8RI EN73)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)