Can I shoot a VOR / DME-A approach without a VOR?

[midlifeflyer]

That statement is supported for VOR, TACAN, or NDB final-approach segments by the AIM passage that Mark quoted in post #30. Is there a passage somewhere that extends it to DME-arc finals?

I suspect no one really cares about the answer for the two anomalous approaches where it's a factor but just for fun, let's try this on. First, let's quote the AIM passage from before, with emphasis.

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.

Next let's quote a definition from the FAR:

"DME" means distance measuring equipment compatible with TACAN.

 

[midlifeflyer]

Half right. Not enough for ILS, but enough for LOC

I read that one a little differently than you do but I can see both interpretations.

 

[midlifeflyer]

So, for LOC/ILS, you *would* have to actually USE the NAV radio for the final approach segment?


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Definitely for ILS. There is nothing permitting substitution of a GPS-generated glidepath to substitute for an ILD electronic glideslope.
@N1120A and I would disagree on the LOC-alone. I would say you have to fly the localizer; he would say you do not.

 

[WDD]

A GPS does NOT replace the glideslope on an ILS.

Can’t the GPS give you the glide slope ?

 

[RussR]

I suspect no one really cares about the answer for the two anomalous approaches where it's a factor but just for fun, let's try this on. First, let's quote the AIM passage from before, with emphasis.

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.

Next let's quote a definition from the FAR:

"DME" means distance measuring equipment compatible with TACAN.

This case is interesting, of course, because doesn't it mean that to fly these two approaches with GPS as your primary, you would HAVE to have an real, no-kidding actual DME receiver onboard to monitor?

 

[smv]

Can’t the GPS give you the glide slope ?

Only if you have a GPS that includes a NAV radio capable of receiving the ground-based signal from the glideslope transmitter (like a 430/530). The calculated glide path that a GPS generates internally is not an ILS glideslope and cannot be used in lieu of an actual transmitted glideslope.

 

[midlifeflyer]

Can’t the GPS give you the glide slope ?

A GPS gives you "a" glidepath.

Don't confuse two things. To use a Garmin 430 as an example, it is a NAV/COM unit with three separate functions and the appropriate hardware for each.. It's a communication radio. It is a GPS navigator. It is a VLOC navigator. When you push that CDI button and switch to VLOC to fly that ILS, you are getting localizer and glideslope signals, not a glidepath created by GPS.

 

[WDD]

Yes. But the Garmin 430 can guide you a glide slope if you fly an LPV approach????

 

[midlifeflyer]

Yes. But the Garmin 430 can guide you a glide slope if you fly an LPV approach????

If it is a WAAS GPS, it can provide a glidepath for an LPV or LNAN/VNAV approach (technically it's not a glideslope).

 

[crash7]

Yes. But the Garmin 430 can guide you a glide slope if you fly an LPV approach????

Yes, but that’s not an ILS. It’s a whole ‘nother approach.


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[smv]

Yes. But the Garmin 430 can guide you a glide slope if you fly an LPV approach????

No. It gives you a calculated glide PATH. A glide slope is associated with the ILS precision approach and is transmitted from ground-based equipment installed on the field and monitored for accuracy. An LPV, although similar in structure, does NOT meet the definition of a precision approach (unless you happen to be taking a checkride and need to be able to demonstrate the ability to follow vertical guidance and you cannot find/use an ILS).

 

[David Megginson]

So back to the OP's question about equipment requirements for flying a VOR/DME approach without a GPS overlay:

• Yes, you may use GPS instead of DME to identify a fix on the approach, so you can fly the approach without operational DME equipment.
  
• No, you may not use GPS instead of VOR for lateral guidance inside the FAF, so you cannot fly the approach without an operational VOR receiver.

I know the OP already figured this out, but I wanted to put it succinctly in one place.

 

[WDD]

So “Slope” is for ILS, and “Path” is LPV.

Slope is not a Path. Although both show you how to descend.

LPV is close - but not as precise as ILS?

 

[smv]

So “Slope” is for ILS, and “Path” is LPV.

Slope is not a Path. Although both show you how to descend.

LPV is close - but not as precise as ILS?

https://www.boldmethod.com/learn-to...nce-between-lpv-and-lnav-vnav-gps-approaches/

 

[midlifeflyer]

So “Slope” is for ILS, and “Path” is LPV.

Slope is not a Path. Although both show you how to descend.

LPV is close - but not as precise as ILS?

Might be as precise as an ILS but the equipment requirements are different.

 

[crash7]

Yeah, but can I log PIC while doing it...?
<insert sarcasm symbol here>


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[N1120A]

Definitely for ILS. There is nothing permitting substitution of a GPS-generated glidepath to substitute for an ILD electronic glideslope.
@N1120A and I would disagree on the LOC-alone. I would say you have to fly the localizer; he would say you do not.

The AIM and IFH disagree with you.

AIM 1-2-3 says you must have a reference to Localizer Raw data, which means monitoring the raw data from the localizer and still being able to fly using GPS as your primary LNAV.

 

[midlifeflyer]

The AIM and IFH disagree with you.

AIM 1-2-3 says you must have a reference to Localizer Raw data, which means monitoring the raw data from the localizer and still being able to fly using GPS as your primary LNAV.

No, you disagree with me.

Like I said, I read it differently than you. I don't see LOC listed with the rest of the navaids in the "you can on the FAS" notes section to begin with. And "use" raw data can mean something different than explicit "monitor" raw data,

OTOH, I know there are those, whose opinions I respect, who say the permissive language about VOR, NDB, and TACAN wasn't needed to begin with. So I'm just saying my read is different, not necessarily that I'm right and you are wrong,

 

[Velocity173]

Why is this thread in the ATC sub forum? A controller will clear you for the approach regardless of your equipment.

 

[MauleSkinner]

The AIM and IFH disagree with you.

AIM 1-2-3 says you must have a reference to Localizer Raw data, which means monitoring the raw data from the localizer and still being able to fly using GPS as your primary LNAV.

The AIM is not the controlling document. Your AFM/Supplement will specify which approaches can or cannot be accomplished using GPS. I know of no system that allows the final segment of localizer-based approaches to be flown using GPS.

 

[MauleSkinner]

What to do if they disagree is one of the mysteries of life.

No mystery...initiate the missed approach, get the airplane safe, and figure out for which one you screwed up the programming/setting.

 

[John Collins]

Where is it written that you can't use GPS as primary LNAV on a DME Arc on the final approach course on the exactly two approaches that exists on?

It is written the the AIM in section 1-2-3, sub paragraph c. Uses of Suitable RNAV Systems., notes 4 and 6. I have quoted the two notes below along with the suitable use number 4. :

4. Fly an arc based upon DME.

Note 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.
...
Note 6. 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.

So note 4 restricts the pilot from substituting for an NAVAID providing lateral guidance for the final approach segment, and includes in parenthesis "(for example, a VOR or NDB)". The example in parenthesis is not an exhaustive list describing all the means of providing for lateral navigation for the final approach segment, as DME is another means as is TACAN. Removing the example in parenthesis does not change the meaning of the sentence. Also, note 6 explicitly states that VOR includes VOR/DME. The KMTN VOR or TACAN RWY 15 approach and the KWAL VOR/DME or TACAN Rwy 10 approach both use DME for the lateral guidance on the final approach segment. So if you have a real DME in the aircraft and are monitoring it, you can use the GPS as well for the DME, but you won't be able to use the GPS to couple to your autopilot using GPSS for LNAV because you won't find either of these approaches in the database as they don't comply with ARINC coding standards, so both the DME and the GPS will only provide a distance number for lateral guidance. The VOR and the DME must both be operational or you won't be able to determine the MAP as it is not a named fix on either of these procedures.

 

[SbestCFII]

https://flightaware.com/resources/airport/ISM/IAP/VOR_DME-A/pdf

So, I got into an argument with someone over this and I have no idea who's right.

I say, the approach plate says "VOR / DME" that means both are required equipment.

He says, you can substitute GPS for DME right?

I say, yeah

He says, then why not for the VOR? It's more accurate than VOR.

I'm so confused.

GPS may be used as a legal substitute for DME and an NDB (fix). GPS is not approved as a substitute for VOR (even if is may be more accurate, but this is debatable). The only case where GPS may be used as the primary means of navigation on a non-GPS approach, is where there is a published GPS overlay.
Example: VOR/DME OR GPS RWY 27 Approach at Tarboro-Edgecombe Airport (KETC)

 

[flyingron]

Yep, and the overlays were a stopgap. Most of them have been replaced with separate RNAV (GPS) approaches. A few do still exist.

 

[Ryan F.]

GPS may be used as a legal substitute for DME and an NDB (fix).

GPS is not approved as a substitute for VOR (even if is may be more accurate, but this is debatable).

The only case where GPS may be used as the primary means of navigation on a non-GPS approach, is where there is a published GPS overlay.
Example: VOR/DME OR GPS RWY 27 Approach at Tarboro-Edgecombe Airport (KETC)

Okay, that's not a correct reply. This is a confusing topic for pilots of all skill levels including CFIIs.

I started replying to SbestCFII and ended up designing an entire graphic and Q&A (and killed my Sunday morning) to try to clear up all of these points. I think in this entire thread, a verbose and completely correct reply has yet to be provided. As such this is a reply to all, not just SbestCFII.



Now, I've been very specific with my terminology above, but I'll be conversational now. Don't nitpick -- if I'm talking about an IFR GPS, you know what I'm talking about for this purpose, an IFR certified GPS which is approved for approaches. The assumption here for the Q&A is that the aircraft is equipped with one.

Q&A​

Q: May I fly a localizer approach using GPS as my navigation reference?
A: No. "The operations do not include lateral navigation on localizer-based courses (including localizer back-course guidance) without reference to raw localizer data." (Note 2)

Q: May I fly a VOR approach using GPS as my navigation reference?
A: Yes, including the final segment, so long as the approach is not NOTAMed NA, the "underlying navaid is operational and the navaid... is... monitored for final segment course alignment." (Note 5) As has been discussed previously here at POA, we know that a bearing pointer on an EHSI would be sufficient, or a backup CDI tuned to the VOR and set in such a way it can monitored for "course alignment."

Q: Well, that sounds like almost the same thing... what's the difference in those two situations?
A: The word "reference" in the former vs. "monitor" in the latter.

Q: I don't think you're right about this, Ryan. Note 4 says I "may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment." That means I need to use my VOR receiver on a VOR approach.
A: I feel your pain, but the notes can't be read in isolation. This entry is like a short story; establishing the basics and then providing the exceptions. From Note 4 the reader must move along to Note 5 to get all the info.

Q: May I fly a DME-arc based approach using GPS as my navigation reference?
A: There are only two approaches in the United States to which this applies, and though they're basically just a curiosity bordering on headache-inducing distraction, yes. You may. The famous "DME arc" approach into MTN is in fact a "VOR or TACAN" approach with a note stating that DME is required.



Therefore there's nothing special about this approach from an equipment perspective. If your aircraft is equipped with an IFR GPS as described above, and you have an operational VOR receiver in the aircraft, the approach is not NOTAMed NA, the "underlying navaid is operational and the navaid... is... monitored for final segment course alignment," you're good to go.

Q: I think you're wrong about that too. Pilots "may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment," according to the AIM! And DME is the lateral guidance.
A: There's no such thing as a DME approach in the United States. Per the title, this is a VOR approach in which DME is required. An IFR GPS may be used in lieu of DME or ADF per Table 1-1-6 in AIM 1-1-17.


Q: I dunno about that... I still disagree...
A: Write your congressman. This approach will likely vanish at some point in the near future and all we'll have are the memories.

Q: May I "monitor" the localizer on a localizer approach and fly it with GPS instead?
A: No. You must reference the localizer. You may use GPS to enhance your situational awareness, which is always allowed.

Q: Can the plane be IFR legal with a GTN 650 but no ADF, VOR, or ILS?
A: A GTN 650 includes navigational radio capability for VOR, LOC, and ILS so if I'm reading between the lines correctly for what you're after, I think the question might better be asked assuming an IFR GPS only, such as a King KLN-94 or even a Garmin GPS 400 (which is a Garmin 430 without the nav/com radios.) If that's the case, yes, subject to the availability of GPS approaches and enroute navigation appropriate to the equipment, weather vis-a-vis alternate airport requirements, the capability of the unit itself (i.e. TSO-C129 vs. TSO-145/146) IFR operations can be conducted legally under certain circumstances with only this equipment.


Phew. I'm done for now.

​

 

[RussR]

Q: I dunno about that... I still disagree...
A: Write your congressman. This approach will likely vanish at some point in the near future and all we'll have are the memories.


​

Good writeup Ryan. But I still disagree with your conclusion about the two DME arc approaches. And I'm not sure what my congressman could do about it.

Regardless of the name of the procedure, the NAVAID "providing lateral guidance for the final approach segment" is clearly NOT the VOR. It's the DME. I don't see how there can be any question about this. Lateral means "side to side", and the DME is what's telling you this. And since it's the DME, to fly this approach correctly with a GPS, by the letter of the regulation, you would have to have a "real" DME receiver to "monitor".

Now, I'd also have no problem flying it with solely GPS as my distance reference, because I think these procedures fall into a regulatory abyss that just hasn't been considered, and won't be because there are only two of these ridiculous approaches around. And it would be perfectly safe to do so. But by my strict reading, it wouldn't be allowed. Of course, strict reading also often results in silly conclusions, like in my thread about circling at BET, Bettles, AK.

As a side note that I believe I've mentioned before, these approaches are also technically misnamed. The one at Martin State should be the "DME OR TACAN RWY 15", with a note "VOR required". However, another aspect of the TERPS design standards is that aircraft are expected to have at least one VOR receiver, so "VOR required" is not necessary. Naming a procedure "DME RWY XX" was never anticipated by the regulations, however, and there is no mention of this being a valid name - and it wouldn't be worth the resulting confusion to change the name of just these two procedures.

As another side note, I see no near-term plan on the IFP Information Gateway to cancel either of these procedures.

 

[Ryan F.]

Good writeup Ryan. But I still disagree with your conclusion about the two DME arc approaches. And I'm not sure what my congressman could do about it.

Regardless of the name of the procedure, the NAVAID "providing lateral guidance for the final approach segment" is clearly NOT the VOR. It's the DME. I don't see how there can be any question about this. Lateral means "side to side", and the DME is what's telling you this. And since it's the DME, to fly this approach correctly with a GPS, by the letter of the regulation, you would have to have a "real" DME receiver to "monitor".

Now, I'd also have no problem flying it with solely GPS as my distance reference, because I think these procedures fall into a regulatory abyss that just hasn't been considered, and won't be because there are only two of these ridiculous approaches around. And it would be perfectly safe to do so. But by my strict reading, it wouldn't be allowed. Of course, strict reading also often results in silly conclusions, like in my thread about circling at BET, Bettles, AK.

As a side note that I believe I've mentioned before, these approaches are also technically misnamed. The one at Martin State should be the "DME OR TACAN RWY 15", with a note "VOR required". However, another aspect of the TERPS design standards is that aircraft are expected to have at least one VOR receiver, so "VOR required" is not necessary. Naming a procedure "DME RWY XX" was never anticipated by the regulations, however, and there is no mention of this being a valid name - and it wouldn't be worth the resulting confusion to change the name of just these two procedures.

Hi Russ, I appreciate it... I figured you'd reply on that topic. I accept your statement on this and you make very good points, and you are of course highly qualified to make them. If the approach were so named ("DME OR TACAN") I think it would be a very different discussion. Are there any approaches in the United States so named? I'm not aware of any.

But since it's not, I'm forced to go by what we have and the regulations which apply to it. This is still a VOR or TACAN approach for which DME is required. That's it, cut and dried.

We can agree to disagree about it from a technical perspective. We're both approaching it from a slightly different regulatory (and practical) perspective. From my vantage point there's no way to drop DME into the bucket of lateral guidance and from yours there's no way to keep it out. It's an approach I've discussed for years more times than I care to count, which is sort of amusing given I've never actually flown it (has anyone here?) Also more or less a one-off, or two-off to be precise, which is going to slide off the radar soon enough. It has been a fun ride as this approach is sort of the platypus of approaches... it doesn't fit cleanly into any category.

 

[John Collins]

I agree with RussR's analysis regarding the two DME arc approaches and not with Ryan F.'s analysis. "A rose by any other name would smell as sweet" does not change the meaning of what is providing lateral guidance on the final approach segment. The VOR is merely providing along track fixes.

Edit: These procedures only provide a number readout for the DME to use for the lateral navigation, but the cross radials are not all in the database as named fixes. The Jeppesen Navdata does not include ZOVAP or MAP or the R068 radial to fly on the MAP procedure. I guess one would have to select BAL on the GPS and use OBS mode to determine the radials without using a VOR or DME. You certainly won't find the procedure in the GPS Navdatabase. Best I could come up with would be entering the following into ForeFlight: SLOAF BAL350015 BAL005015 CUMBE GOVES BAL047015 BAL060015 BAL068015 BAL068011 BOAST.

 

[Ryan F.]

I agree with RussR's analysis regarding the two DME arc approaches and not with Ryan F.'s analysis. "A rose by any other name would smell as sweet" does not change the meaning of what is providing lateral guidance on the final approach segment. The VOR is merely providing along track fixes.

I think we'd all be in agreement if the approach was named as RussR suggested it ought to be. In lieu of that, it's a "VOR or TACAN" approach with DME as "required equipment". The underlying navaid is the VOR and the DME requirement may be adhered to just as it might on any other approach, in terms of using other equipment (a suitable RNAV system) in-lieu.

That said, I think it's okay to disagree here. It really comes down to which note takes precedence in the mind of the user. You and RussR favor that the "lateral guidance for the final approach segment" must come specifically from the DME and therefore actual DME itself is required and a suitable RNAV system may not be used in lieu of that. I understand why it's tempting to go down that road, because looking at it in a very practical sense, that seems to be what the various notes are telling you. After all, left and right is lateral, and lateral in this case is DME... right? So therefore it can't be replaced by a "suitable RNAV system..." Right?

But I believe it's technically incorrect because DME (along with ADF) is equipment which is specifically designated as "in-lieu" in TBL 1-1-6. In other words, required equipment which can be substituted by a "suitable RNAV system." VOR does not appear on this list. It cannot be substituted by a suitable RNAV system. It is an underlying navaid which must be monitored if not used for reference. There are other pointers. Note 1 states "The allowances described in this section apply even when a facility is identified as required on a procedure (for example, “Note ADF required”)." And Note 6 states "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."

It really boils down to the fact that the underlying navaid you're using for this approach is VOR or TACAN. That is how the approach is named. The VOR-DME (BAL, 115.1) provides primary guidance for the approach. There is no provision I can find anywhere which would contradict the simple interpretation of the approach procedure itself, including the required equipment, along with the aforementioned AIM references.

It's a fun discussion almost devoid of any practical value other than extremely intricate parsing of guidance which wasn't designed for this "platypus."

Edit: These procedures only provide a number readout for the DME to use for the lateral navigation, but the cross radials are not all in the database as named fixes. The Jeppesen Navdata does not include ZOVAP or MAP or the R068 radial to fly on the MAP procedure. I guess one would have to select BAL on the GPS and use OBS mode to determine the radials without using a VOR or DME. You certainly won't find the procedure in the GPS Navdatabase. Best I could come up with would be entering the following into ForeFlight: SLOAF BAL350015 BAL005015 CUMBE GOVES BAL047015 BAL060015 BAL068015 BAL068011 BOAST.

Correct... the user would be expected to simply use the VOR as a waypoint in the GPS and reference GPS distance from the VOR to determine DME. If you wanted to "build" an approach in FF using user waypoints that's up to you... don't know if I'd go to that amount of trouble myself.

 

[John Collins]

I guess we will have to agree to disagree as the wording is quite clear to me. BTW this whole area is being re-written and a new AC and corresponding updates will eventually make it into the AIM.

 

[Ryan F.]

It's anything but clear, but the conclusion is inescapable - to me. Agreeing to disagree is fine, no rancor here, just stimulating conversation. It will be interesting to see what new guidance may be introduced.

 

[Palmpilot]

It seems to me that the question is answered by AIM 1-2-3(c), Note 4, as quoted above, which says, in part, "Pilots may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment." The use of the words "for example" tells us that "VOR or NDB" are examples, and thus cannot be assumed to be a COMPLETE list of navaids that this restriction applies to. Furthermore, I don't see how "VOR or TACAN" in the title of the MTN approach can negate the fact that the DME portion of the TACAN is what provides lateral guidance on the final approach segment.

If you tried to fly this approach with nothing but VOR receivers and no GPS, there would be no way to ensure that you stayed on course laterally. Therefore DME is the navaid "providing lateral guidance on the final approach segment," and thus by the wording of the note you are not allowed to substitute GPS for DME once you pass the final approach fix.

 

[Ryan F.]

It seems to me that the question is answered by AIM 1-2-3(c), Note 4, as quoted above, which says, in part

Yes, hence my light-hearted "write your congressman" remark... not the first time I've had this discussion...

Look, as stated above, I understand the appeal of this interpretation. In isolation, Note 4 appears to support your conclusion. But the notes must be read in totality and correlated with other sections of the AIM for comprehensive understanding.

The issue is this: it's a VOR approach with a VOR-DME as the "underlying navaid." DME is required equipment, the functions of which may be provided by a "suitable RNAV system" per TBL 1-1-6.

But only so many angels may dance on the head of one pin, and differing conclusions won't hurt anything in this unique case.

 

[dtuuri]

The use of the words "for example" tells us that "VOR or NDB" are examples, and thus cannot be assumed to be a COMPLETE list of navaids that this restriction applies to.

Is DME really a "NAVAID"? The P/CG says a NAVAID provides "point to point" navigation, doesn't it? Does a DME? I think a DME can only take you back where you began and won't even tell you when you arrive.

Furthermore, I don't see how "VOR or TACAN" in the title of the MTN approach can negate the fact that the DME portion of the TACAN is what provides lateral guidance on the final approach segment.

Doesn't a VOR provide guidance on the MTN approach too? How will you know when to descend to the next lower MDA if the DME is welded on 14.7 all of time unless you're guided by the VOR? Looking at the plan view—the stepdown fixes are laterally separated just like the on a VOR approach. I think I'm a gonna go with Ryan.

 

[Palmpilot]

Doesn't a VOR provide guidance on the MTN approach too? How will you know when to descend to the next lower MDA if the DME is welded on 14.7 all of time unless you're guided by the VOR? Looking at the plan view—the stepdown fixes are laterally separated just like the on a VOR approach. I think I'm a gonna go with Ryan.

The note restricts substitution of GPS for "lateral" guidance. Using the VOR to identify stepdown fixes is not lateral guidance, it's along-course guidance, and therefore you can substitute GPS for that purpose along the entire approach path.

I wouldn't do it, but you guys can substitute GPS for that DME-based final approach course if you want; I won't snitch!

 

[Palmpilot]

Here's a question that ought to be good for another couple of pages:

I've noticed that loading an ILS approach in a G1000 gives a message saying that the GPS can only be used for monitoring, or something like that. If it gives the same message on this approach, would that change your answer?

 

[dtuuri]

The note restricts substitution of GPS for "lateral" guidance.

The VOR is the primary NAVAID. Usually, those NAVAIDs provide "lateral guidance" and DME provides "along track" info. Here, they're flipped, so I'm sticking with the obvious intent (to me) and going with the primary NAVAID that can't be substituted.

 

[Palmpilot]

The VOR is the primary NAVAID. Usually, those NAVAIDs provide "lateral guidance" and DME provides "along track" info. Here, they're flipped, so I'm sticking with the obvious intent (to me) and going with the primary NAVAID that can't be substituted.

The note says you can't use GPS for "lateral guidance" on the final approach segment. It doesn't say anything about the "primary navaid."

Also, aren't you required to have lateral guidance on a CDI display in order to use a GPS to fly an approach? What if the GPS won't do that on this approach?

 

[Ryan F.]

The VOR is the primary NAVAID. Usually, those NAVAIDs provide "lateral guidance" and DME provides "along track" info. Here, they're flipped, so I'm sticking with the obvious intent (to me) and going with the primary NAVAID that can't be substituted.

You've cottoned onto it. That's the reason for the confusion -- the notion that DME, specifically and solely, provides the "lateral guidance for the final approach segment" and therefore an actual DME receiver must be installed in the aircraft and monitored. But the underlying navaid is in fact a VOR-DME, so named as an approach ("VOR or TACAN") with required equipment ("DME required"). Further, that navaid is being monitored if the pilot is correctly following the provided guidance, and as you've pointed out radials do provide the location of step-down fixes.

With ground-based navaids being used for a given approach the primary considerations are a) the navaid is operational, b) the approach is not NOTAMed NA (Note 4), not affected by an expired or unsatisfactory flight inspection (note 4), or based on a recently decommissioned navaid (note 4). The navaid in question here is BAL.

Since a VOR receiver is available in our scenarios, as a result GPS is not a substitution for the underlying navaid. It allows for the VOR to be monitored. And the GPS may be used in lieu of DME per TBL 1-1-6.

 

[Ryan F.]

The note says you can't use GPS for "lateral guidance" on the final approach segment. It doesn't say anything about the "primary navaid."

Also, aren't you required to have lateral guidance on a CDI display in order to use a GPS to fly an approach?

No. It could be a bearing pointer, or it could be an electronic CDI (think NAV 1 page on a GNS430W). In the case of DME, there is no stated requirement. It's just DME.

What if the GPS won't do that on this approach?

It's not a "what if," the GPS will NOT display course deviations because you cannot load this approach in a G1000, GNS430, etc. You'd have to simply use the GPS as a basic DME tool.