CFII Debate - GPS in lieu of DME

First.. DPE's don't teach.
They do, indirectly, because their enforce standards and you can often find out what these standards by requesting clarification before your scheduled exam.

if it’s published, it’s mandatory....
The only "mandatory" thing about them per my reading is that you are not supposed to commence descent before you reach such VDP, all provided you have equipment aboard to identify a VDP.
 
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Both.
Let me chime in since I know under what circumstances the original question arose (Keith happens to be my CFII).
We fly G1000 equipped SR20. I never saw any VDPs displayed in G1000, regardless if published or not. I have no idea why G1000 doesn't display published VDPs but this happens to be the case. So the way I happen to identify published VDPs is to watch the GPS distance to RWY XX map because this is the distance you always get from G1000 - and this is the distance you always get on approach chart (for example 2.2 nm at airport O69, RNAV approach). So for example in case of this LNAV approach the only way for me to identify VDP is to wait until RWY29 map becomes active waypoint and wait for the distance to count down to 2.2.

But at KLVK, LOC RWY 25R since the published VDP is identified explicitly through the localizer distance 2.9 nm and our SR20 is not DME equipped and doesn't give you this distance - I again resorted to using the published VDP to threshold (gps) distance (2 nm) that some very senior CFII in the club considered unacceptable.
Does the very senior CFII consider your RNAV approach acceptable? If so, is he saying you could identify the VDP on the localizer with a GPS distance from ILVK?

For what it's worth, the FMSs that I've used didn't have HINIX or ZABGO in the database's LOC procedure...they had to be identified by DME or GPS distance.

Edit: The AIM states
(12) If a visual descent point (VDP) is published, it will not be included in the sequence of waypoints. Pilots are expected to use normal piloting techniques for beginning the visual descent, such as ATD.
 
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First.. DPE's don't teach.

Second... the GPS as DME is commonplace. The question is what you tune the GPS to. Are you putting the airport or the navaid the DME distance is measured from? [the second answer is correct]

If you're flying, per chance, the LOC/DME RWY 24 http://155.178.201.160/d-tpp/1801/05136LD24.PDF

You'd have the GPS tuned to IFUL for distance information only and the nav set to 108.9 with approach course 243 on the CDI.

Fly the needles and reference the GPS only for distance information. Kinda like having a DME for distance information.

Hmm.. why does this question keep coming up?

First, I know several DPE's that are CFIIs, and I was addressing all of them smartass.
Second, duh.
Third, this question comes up because I have 2 conflicting views (CFIIs and DPEs) on this in my FSDO and I was looking for some intelligent dialogue, not a ego based reply. Some of us here have knowledge and experience that I'd like to hear.
 
The use of GPS in lieu of ADF or DME was originally approved for the TSO C129 (non-WAAS) receivers such as the KLN90, 89b, 94, Garmin 155, original 430/530, etc. Under those rules, when using GPS in lieu of DME (or ADF) the active waypoint on the GPS was required to be the location of the DME transmitter. If you were flying an LOC/DME approach, then you would tune the Localizer in your NAV radio and the DME source in the GPS. In the plan view for the LOC/DME RWY 5 at KHRJ, you would Tune the Localizer 108.35 on NAV 1 and set the GPS Waypoint IHRJ on the GPS. On the moving map models, you would then select OBS mode and set the inbound course 048 for situational awareness. In this configuration, the miles to the DME station would be virtually the same as using DME. On newer units such as the 430/530W, 650/750, when selecting non-GPS approaches, the unit "overlays" a GPS depiction of the approach and the provides "countdown" distances to each waypoint, which will differ from the chart, but are pretty intuitive to figure out.

LOC-DME-HRJ.png
 
What is the rationale of the ones who don't allow it?
I went through this with a CFII on an IPC. He was wrapped up in the LOCDME being down yonder at the far end of the runway. He thought that because of that you could not use GPS to identify the DME fixes on the approach. For instance there's a fix on the LOC-D Approach to KSEE, DEBEY. It's the 4.0 DME fix from ISEE. It's 3.1 miles to the next fix which is the Missed Approach Point at the runway. I could not convince him that when the GPS said we are over DEBEY, we are over DEBEY and it is an authorized substitute for DME. He just couldn't get past it saying 3.1 (to the next fix) when the DME fix was 4.0 to the DME antenna. This all came up when the DME in the plane took a dump. I said we can load and activate the Approach in the 430 and do it (the localizer of course being monitered with VLOC.) The only thing I can think of that would dispute that would be some directive that talks about 'slant range' but I've never seen that.
 
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and set the GPS Waypoint IHRJ on the GPS
I don't think it is possible, at least not in G1000, I tried with the localizer at KLVK (I am now checking it on my G1000 PC Trainer)- ILVK and G1000 can't find such a thing.
 
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GPS uses lateral distance while DME gives slant distance - consider the case of being overhead of a beacon. However, it is allowed in the rules, so legally can be used unless otherwise stated.

True. But at 5 miles and 1,000' HAT, the difference is about 19', or 2/3rds the length of a typical GA airplane, and a fraction of a second in timing.
 
What is the regulatory function of a VDP on an approach?

The VDP is a recommended point at which you should execute the missed approach procedure on a non-precision approach. The VDP is a distance from the threshold and it's distance from the threshold is calculated by taking the MDA height above the touch-down zone and dividing it by 300. In the example Profile view below, the MDA is 600' (Cat A) and the TZDE is 195'. 405/300 = VDP of 1.35 NM from the threshold. The VDP position allows a reasonable rate of descent from the VDP to the runway (the 300 represents 300' per NM). If you're past the VDP, then your descent rate would have to be higher and that could make a safe descent to landing more dicey. That's why it's a recommended point to execute your missed approach.
 
I don't think it is possible, at least not in G1000, I tried with the localizer at KLVK (I am now checking it on my G1000 PC Trainer)- ILVK and G1000 can't find such a thing.
Strange, I can enter ILVK at Livermore as a waypoint on my Garmin Pilot Software. I'll check it out on my 430W tomorrow.
 
Strange, I can enter ILVK at Livermore as a waypoint on my Garmin Pilot Software. I'll check it out on my 430W tomorrow.
Strange indeed!
I finally actually succeeded, I was "flying" west of KLVK and then it refused to load but as soon as I positioned myself east of the airport (sort of ready to fly the LOC) - it did load!!
Hmmm.. not sure why it is so fussy.
 
The VDP is a recommended point at which you should execute the missed approach procedure on a non-precision approach.

...snip...

That's why it's a recommended point to execute your missed approach.
No it isn't. I hope that's not what you're teaching.

The missed approach point is the mandatory point at which you should execute the missed approach if you're not in position to land (AIM 5-4-21). In fact, I would say that it may be dangerous to execute the missed approach procedure prior to the MAP because terrain clearance isn't guaranteed in the case of an early turn.

So, what I was taught was if you don't have the field in sight at the VDP, realize that you are more than likely going to have to go missed, and if in fact you decide to go missed at that point, you could start the go-around (climb) portion immediately, but you must follow the final approach guidance to the MAP before you start the missed approach procedure's lateral guidance.
 
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We have discussed this before.
It has always been my belief that if it’s published, it’s mandatory.... But one should always calculate one as good practice.
Mandatory for what? With a reference, please.
 
Because the FAA has made it very clear that:

operators may use a suitable RNAV system in the following ways.

(4) Fly an arc based upon DME.​

It's interesting that you quoted AIM-1-2-3(c), but stopped short of the exceptions to it. While the text says you can do it, notes 2-5 contains the few exceptions when you cannot.

2. These operations do not include lateral navigation on localizer-based courses (including localizer back-course guidance) without reference to raw localizer data.

3. Unless otherwise specified, a suitable RNAV system cannot be used for navigation on procedures that are identified as not authorized (“NA”) without exception by a NOTAM. For example, an operator may not use a RNAV system to navigate on a procedure affected by an expired or unsatisfactory flight inspection, or a procedure that is based upon a recently decommissioned NAVAID.

4. Pilots may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment. This restriction does not refer to instrument approach procedures with “or GPS” in the title when using GPS or WAAS. These allowances do not apply to procedures that are identified as not authorized (NA) without exception by a NOTAM, as other conditions may still exist and result in a procedure not being available. For example, these allowances do not apply to a procedure associated with an expired or unsatisfactory flight inspection, or is based upon a recently decommissioned NAVAID.

5. For the purpose of paragraph c, “VOR” includes VOR, VOR/DME, and VORTAC facilities and “compass locator” includes locator outer marker and locator middle marker.

The specific example that I've seen before for this is the DME approach to KMTN.

It's a picky exception, so I assume there must be a really good reason for it.
 
It's interesting that you quoted AIM-1-2-3(c), but stopped short of the exceptions to it. While the text says you can do it, notes 2-5 contains the few exceptions when you cannot.



The specific example that I've seen before for this is the DME approach to KMTN.

It's a picky exception, so I assume there must be a really good reason for it.
I didn't do the exceptions because none of them apply to the discussion so far.

Actually, I wasn't quoting AIM 1-2-3. I was quoting AC 90-108

And you are quoting an 2-year old copy of the the AIM. Your #5 is now #6. #5 now reads:
Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN or NDB signal, is allowable. The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment.​
 
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There are only two approaches in the country you can't use the GPS substitution:
KMTN VOR/DME OR TACAN Z RWY 15
KWAL VOR/DME OR TACAN RWY 10
Both use the DME for the final approach course. Both have a bunch of other approaches.
How were you able to find that those are the only two? I've tried to do searches like that about a particular feature of Approaches but couldn't find a way to do it.
 
The VDP is a recommended point at which you should execute the missed approach procedure on a non-precision approach.

No it isn't. I hope that's not what you're teaching.
...
In fact, I would say that it may be dangerous to execute the missed approach procedure prior to the MAP because terrain clearance isn't guaranteed in the case of an early turn.

I also would like to see @SbestCFII 's reference for that. I have never seen anything indicating the VDP is a recommended point to begin the missed approach, and in fact, as @Sluggo63 points out, it may be dangerous.

Doing so is contrary to the design standards for missed approaches. For ground-based approach (VOR, LOC, etc.), a turning missed approach is only evaluated and protected for an early turn starting 1 nm prior to the MAP. It is sometimes more, but 1 nm is the normal value. For a non-WAAS GPS approach (LNAV), that value is only 0.3 nm. And for an LP approach, it is just 40m prior to the MAP. So, if on any of these you start a turning missed approach at 1.35 nm prior to the MAP, you are in actual danger of running into something.

(Ref: 8260.3C, para 2-8-6 and 8260.58A, para 3-7-3 along with others)

Now, if you want to start a climb only at the VDP, nothing wrong with that. But understand that a VDP is most often based on a 3.0 degree glidepath. Especially Cat A and B aircraft are capable of descending steeper than that safely. In fact, the FAA specifies that a Cat A-only procedure could have up to a 5.70 degree glidepath. Cat B is up to 4.20 degrees. (8260.3C, table 2-6-1) Since the main requirement on when to leave MDA is that it permits a descent to the runway using a "normal" descent (91.175c(1)), I would argue that anything up to a 5.70 degree descent angle is "normal" for Cat A, and 4.20 for Cat B. I've always considered that to be the pilot's call as to whether the descent can be made "normally". But for Cat A and B at least, 3.0 degrees is actually a pretty shallow descent.

Of course, if company rules/OPSPECS/other requirements restrict this, that's different. I'm talking about small aircraft and Part 91 operations here.
 
I don't think it is possible, at least not in G1000, I tried with the localizer at KLVK (I am now checking it on my G1000 PC Trainer)- ILVK and G1000 can't find such a thing.
Every Garmin database has the localizers that have DME. The database does not have localizers that do not have DME. Thus, no ILVK
 
First, I know several DPE's that are CFIIs, and I was addressing all of them smartass.

If the person is both a CFII and a DPE, they only TEACH as a CFII. DPE's may or may not keep their CFI current. Reference: https://www.faa.gov/other_visit/aviation_industry/designees_delegations/individual_designees/dpe/

Second, duh.

Pointing out that it is a common practice and how to do it referencing an approach plate gets a "duh"? Great, you already knew it. Leading swiftly to 3: Why did you ask?

Third, this question comes up because I have 2 conflicting views (CFIIs and DPEs) on this in my FSDO and I was looking for some intelligent dialogue, not a ego based reply. Some of us here have knowledge and experience that I'd like to hear.

I'm sorry your initial inquiry of "some of us here" is a topic that is as common as High wing vs Low wing.
 
Every Garmin database has the localizers that have DME. The database does not have localizers that do not have DME. Thus, no ILVK
Like I said - it ultimately worked, ILVK was in the database.
 
I also would like to see @SbestCFII 's reference for that. I have never seen anything indicating the VDP is a recommended point to begin the missed approach, and in fact, as @Sluggo63 points out, it may be dangerous.
I'm guessing he means "forget about landing and follow the missed approach procedure (which begins at the MAP) treat it as a missed approach" rather than, "turn right now into that mountain."
 
How were you able to find that those are the only two? I've tried to do searches like that about a particular feature of Approaches but couldn't find a way to do it.
I hear voices.
 
I said “it has always been my belief”. If I had a reference for you I would have stated it as fact.

Does it not bother you that you've got this "belief" about a regulatory issue that you can't support with a regulatory reference?
 
Does it not bother you that you've got this "belief" about a regulatory issue that you can't support with a regulatory reference?
No. If it’s not regulatory it still errs on the side of safety. Plus I would calculate, and use a VDP regardless if one is not published. So it’s a win-win the way I see it.
 
If the person is both a CFII and a DPE, they only TEACH as a CFII. DPE's may or may not keep their CFI current. Reference: https://www.faa.gov/other_visit/aviation_industry/designees_delegations/individual_designees/dpe/

Personally, I teach as myself, and sign paperwork as a CFI. :)

DPEs can teach, just not during evaluations. They may or may not be able to sign stuff saying they taught.

;)

(I’m just having fun with you, nitpicking here... haha. But honestly I’ve met pilots with no CFI who could teach people things... and honestly I’m sure there will be at least one person somewhere sometime who will say I couldn’t teach them ****, CFI certificate or not. Hahaha. Yay, humans... haha.)

Context counts. FAA says certain people can teach AND sign logbooks.

In reality, I can’t think of a single checkride that I didn’t learn something. Or any flight, really. :) Sometimes it’s just, “I never realized water pooled there in this particular tie-down spot... good to know if the temp is going to be below freezing.

I learned one night how to unfreeze chocks stuck in ice around a tire with hot water from the FBO coffee pot. :) :) :) There’s no signature from anyone in my Logbook about it, but it’s a useful skill for an aviator. Hahaha. :)
 
I didn't do the exceptions because none of them apply to the discussion so far.

Actually, I wasn't quoting AIM 1-2-3. I was quoting AC 90-108

And you are quoting an 2-year old copy of the the AIM. Your #5 is now #6. #5 now reads:
Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN or NDB signal, is allowable. The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment.​

Yeah, I quoted the older AIM the last time this topic came around too. Maybe one day I'll get it right.

The wording is a little different, but AC 90-108 contains the same restrictions on lateral guidance as the AIM. Or vice versa if you prefer.

I think the point to the larger discussion is that while GPS can generally be used for DME, there are exceptions. Both sides have something right and something wrong.
 
Indeed it is. They didn't used to do that with for ILS that didn't have collocated DME.

Probably related to their new “Visual” feature in the newer units that builds an unofficial 3 degree glide path to a great many runways.

I’ve been playing with it on the GTN, it’s pretty nifty. With understandable limitations of course. They warn you on the screen about those and you have to accept it right after you pick the runway you want.
 
Yeah, I quoted the older AIM the last time this topic came around too. Maybe one day I'll get it right.

The wording is a little different, but AC 90-108 contains the same restrictions on lateral guidance as the AIM. Or vice versa if you prefer.

I think the point to the larger discussion is that while GPS can generally be used for DME, there are exceptions. Both sides have something right and something wrong.
You are right, of course.

This copy of the AIM is always up to date
 
No. If it’s not regulatory it still errs on the side of safety. Plus I would calculate, and use a VDP regardless if one is not published. So it’s a win-win the way I see it.
There is one, btw. It's in Part 121 for the airline guys (121.651). It says they can't start the descent from the MDA until reaching the charted VDP (the supposed point for a normal approach and landing) unless they can't make a normal approach or landing if they wait until they reach it. Aside from the apparent practical contradiction, notice, there's nothing one way or the other about waiting until after reaching it.

I don't disagree with any practical point you made. I also use the VDP when available or roll my own. Very, very useful. My only point is, the idea that a VDP is an exception to the use of GPS in lieu of DME doesn't pass the "silly" test.
 
Probably related to their new “Visual” feature in the newer units that builds an unofficial 3 degree glide path to a great many runways.

I’ve been playing with it on the GTN, it’s pretty nifty. With understandable limitations of course. They warn you on the screen about those and you have to accept it right after you pick the runway you want.
Then again, it could be a mistake. I checked ICNO and IECC. They are not in the current database. Where a collected ILSDME is in the database the location is the DME, not the LOC antenna. There is a small difference.
 
Indeed it is. They didn't used to do that with for ILS that didn't have collocated DME.

Well, it's good that I-LVK has a colocated DME then. At least as I recall my instrument training that's what the Channel number in the Localizer frequency box means and the I-LVK with DME distances along the profile view.

http://www.chartbundle.com/qc/klvk-loc
 
Well, it's good that I-LVK has a colocated DME then. At least as I recall my instrument training that's what the Channel number in the Localizer frequency box means and the I-LVK with DME distances along the profile view.

http://www.chartbundle.com/qc/klvk-loc
Correct. The Jeppesen chart is in error, because it doesn't show ILS DME, which is their way of portraying instead of the DME channel. I should have looked closer because the Jepp profile does shoe ILVK DME fixes. So, back to the original thesis. Only ILS-DME localizers are in the Garmin nav database. Off to report it to Captain Jepp.
 
No it isn't. I hope that's not what you're teaching.

The missed approach point is the mandatory point at which you should execute the missed approach if you're not in position to land (AIM 5-4-21). In fact, I would say that it may be dangerous to execute the missed approach procedure prior to the MAP because terrain clearance isn't guaranteed in the case of an early turn.

So, what I was taught was if you don't have the field in sight at the VDP, realize that you are more than likely going to have to go missed, and if in fact you decide to go missed at that point, you could start the go-around (climb) portion immediately, but you must follow the final approach guidance to the MAP before you start the missed approach procedure's lateral guidance.
I am pretty sure that was what he meant. No instructor would teach executing the MAP at the VDP.
 
I'm guessing he means "forget about landing and follow the missed approach procedure (which begins at the MAP) treat it as a missed approach" rather than, "turn right now into that mountain."
I am pretty sure that was what he meant. No instructor would teach executing the MAP at the VDP.
What he meant doesn't matter. What he says (typed) matters, especially when instructing. Words have meanings and they matter.

This is what he said:
The VDP is a recommended point at which you should execute the missed approach procedure on a non-precision approach.

If I was a brand-new instrument student and @SbestCFII told me that the VDP is the "recommended point at which you should execute the missed approach procedure on a non-precision approach." That would sound pretty unambiguous to me. I should execute the missed approach procedure at the VDP on a non-precision approach. Except that is wrong. And dangerous.

What he should say is that if you reach the VDP and you are not in a safe position to land you could (not mandatory to do so) begin your climb to the missed approach altitude, but you must follow the final approach guidance to the Missed Approach Point before executing the missed approach procedure.

When instructing, there should be no "what I think my instructor means is..." or "I'm guessing he meant..."
 
Even if you have the field in sight, you should not be descending below MDA until,past the VDP. Please don’t teach anyone this is the point at which you go missed approach, especially on average the VDP is around 1NM from the runway.

VDP
The Visual Descent Point (VDP) is a defined point on a straight-in, non-precision approach from which you can descend below the MDA, as long as you have the required visual reference. If a VDP is available, it will be indicated by a "v" on the profile view portion of the instrument approach procedure chart. Do not descend below MDA before reaching the VDP.

https://www.faasafety.gov/gslac/alc/libview_normal.aspx?id=17273
 
Even if you have the field in sight, you should not be descending below MDA until,past the VDP. Please don’t teach anyone this is the point at which you go missed approach, especially on average the VDP is around 1NM from the runway.

VDP
The Visual Descent Point (VDP) is a defined point on a straight-in, non-precision approach from which you can descend below the MDA, as long as you have the required visual reference. If a VDP is available, it will be indicated by a "v" on the profile view portion of the instrument approach procedure chart. Do not descend below MDA before reaching the VDP.

https://www.faasafety.gov/gslac/alc/libview_normal.aspx?id=17273
I have heard people consider a VDP a missed approach point. Reason being is because if they are past it they cannot make a normal descent and land in the touchdown zone. Now, not sure how part 91 guys look at that, but it is an unofficial MAP for commercial ops. Let me rephrase... Not so much a MAP, but rather a decision point. if you don’t see it by this point you’re not landing.
 
Even if you have the field in sight, you should not be descending below MDA until,past the VDP.
This isn't quite true either (if you're talking about the published VDP). If there is more than one line of minima on an IAP, the VDP that is published is based on the lowest MDA. If there are minima lines for Cat's A-D and you're in a Cat D airplane, the published VDP is for the Cat A minima. Waiting until you're at the VDP may put you late descending. You'd have to start down before the published VDP to have a normal descent to the runway.
 
I'm a little late to the thread and I might have missed it in case someone else mentioned it, but the key point here might be specific to the wording in the OP's post about the MFD.

I taught the G1000 many moons ago so I don't remember (and I'm not going to dig through the G1000 manual either, sorry) but there may be limitations on which information can be used based on where it is portrayed in the aircraft.

The real world example I can provide is in one of my work aircraft, the Gulfstream 450. The avionics suite is the Planeview, a dressed-up version of the Primus Epic by Honeywell. We can configure our DUs (screens) to display all kinds of different information in different panels. One of these displays is a VSD, or Vertical Situation Display, which goes on one of the MFDs. We use this a lot on arrivals with speed and crossing restrictions... some SIDs too.

But the data on this screen is purely "advisory only" and we must reference the speeds and altitudes from the FMS as well as follow VNAV guidance on our ADI irrespective of the VSD's display. And there's a good reason for it. Sometimes the VSD is flat out wrong. (shrug) Blame Honeywell.

This may be true of the MFD in the G1000 as well; information displayed there may be advisory, and the data may need to be referenced on the GPS unit itself. Not saying that's what's happening, but there are precedents for that, and it wouldn't shock me.

Otherwise, of course GPS can be used in lieu of DME. There are no restrictions on that in the United States. VOR and NDB approaches need raw data 'monitoring' (usually in the form of a bearing pointer) on someone's HSI) but that's it.

I was a little surprised to see the discussion about the VDP in relationship to the MAP. You should never go missed at the VDP. That's the point at which you start realizing you're most likely going to be flying the missed approach so you can prepare for it. By the time you cross the MAP, you're ready to fly it.

And that's that.
 
Found this in the Cessna 172S G1000 limitations:

"Use of the NAVIGATION MAP page for pilotage navigation is prohibited. The Navigation Map is intended only to enhance situational awareness. Navigation is to be conducted using only current charts, data and authorized navigation facilities."

Was the OP referencing distances portrayed on the "NAVIGATION MAP" display, I wonder?

Even so it's a stretch given the specific terminology provided... after all, "pilotage navigation" doesn't sound like IFR to me. The whole thing is likely a tempest in a teapot, that is unless there is an actual limitation to using the MFD for referencing GPS distances or other navigation data beyond what is posted here (i.e. something from Garmin) -- ala the example I posted above.
 
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