Local area flight planning

[FlyDave]

Yesterday morning I went out with my friend Jerry (jerry-N5911Q) to get some IFR practice in actual conditions. We get a marine layer early morning this time of year that is usually no more than 500' thick so there is some actual to be had.
I fly out of Petaluma, o69, and there are a couple of airports fairly close where we regularly do approaches - Sanata Rosa KSTS and Novato KDVO. Santa Rosa has an ILS to runway 32 and the marine layer was starting to thin out to the north so I got my clearance and did the ODP at Petaluma witch took us to Skaggs Island VOR (SGD) then vectors to an approach into KSTS. I listened to ATIS at STS and it said the ILS was OTS but didn't list which approach was in use. I asked ATC and they said to expect the RNAV runway 02. So I pull up the approach and brief it and load it into the 530. This approach is WAAS and under minima shows "LP MDA", "LNAV MDA" and "CIRCLING".
If you look at the approach plate for the GPS rwy 13 at KDVO, it is not WAAS and under minnima  only lists S-13 or circling. When you fly this approach with a WAAS GPS you get a glideslope when you cross EYEJI (FAF).
So I get set up for the RNAV (GPS) Rwy 02 at STS and, since we get a glideslope on the RNAV GPS 13 approach into KDVO, crossing the FAF I'm expecting a glidslope. Guess what - NO GLIDESLOPE. Looking at the approach subsequently and finding MDA I should have planned on stepdowns and no glideslope - but that wasn't my reality. So I quickly realize I don't have a glideslope and start down for the next stepdown. I'm a little bit of assholes and elbows at this point trying to make up for lost descent distance and time. I finally get down to a little under 600' (almost 100' still above MDA of 500') but I've just passed the MAP and don't have the ground in sight, so we go missed. We're above the layer in about 15 seconds and get vectored back for the LPV approach into Petaluma where the marine layer is burning off and we get home without an issue.
I'm posting this to point out a couple of things about my flight yesterday:

• Since I was going to do "the usual approaches" we do, I didn't brief anything ahead of time. Had I looked at the NOTAMs I would have known that the ILS was OTS - along with any other NOTAMS.
• Had I known that the ILS was OTS I <<should>> have briefed the other possible approaches and understood what to expect.

This was good practice for me as it opened my eyes to the importance of flight planning (including checking NOTAMs and looking over the available approaches) - even in my local area where I "know the airports".

A question for the group; Look at these two approaches:

• RNAV (GPS) RWY 12 at KSTS lists WAAS
• GPS RWY 13 at KDVO doesn't list WAAS

Why do we get a glideslope on the non-WAAS approach and no glideslope on the WAAS approach?

 

Dave
 

KSTS RNAV (GPS) RWY 02.PDF

KDVO GPS RWY 13.PDF

[flyboy0681]

I guess I'm still too green behind the ears, but I pore over every NOTAM along my route. Just two days ago while planning a flight to Tuscaloosa, Alabama, I looked at the destination NOTAM and noticed that the Crimson VOR was out of service and that the missed approach fix was changed to another VOR 15 miles to the east. Not sure what would have been had I needed to go missed and headed for a fix that was OTS. At the very least a ASRS report, at most a shout out from the Birmingham controller to "copy down this phone number and call when on the ground".

 

But to answer your question, I think the glideslope answer is that the non-WAAS glideslope is provided by a mathematical calculation made within the box itself while the WAAS obviously is dependent on land based signals. Maybe the location of the airport doesn't provide for a reliable enough signal. Having flown out of Novato myself for a few years, it may be the the foothills in the area are blocking the signal.

[Danb]

Dave a very valuable day for you, you went for some IFR practice and instead learned the value of planning ahead, and at the least more planning ahead. This kind of experience you picked up is something the will stay with you forever. I feel you had a great day and the experience gathered was much better than nailing an Ifr procedure with no thought. As our flying days continue our brains will retrieve these items without much thought..it also shows one that whenever we turn the keys we generally learn something.....

[MooneyBob]

And that's why I try to do my currency approaches in the actual IMC whenever possible. Usually we can find one or two nice 1000-2000' IMC weekends within 6 months here around the NE area.

[Jerry 5TJ]

I think the answer is

 

(1)  the non-precision approach (GPS 13 to KDVO)  is permitted to have an advisory glide slope (LNAV+V) calculated but it is still a non-precision approach and retains its (high) MDA.   According to Max Trescott, the FAA has found that the "Dive and Drive" step-down approaches are more dangerous than those where smooth descent is flown, hence the LNAV+V is built into GPS receiver databases when possible. 

 

There is  no LPV to KDVO because there is a hill in the way that blocks straight-in approaches and some more hills and towers on the missed approach path.  The MDA is about 1000' AGL, not a very low minimum. 

 

(2)  The precision approach you flew (LP to runway 2 at KSTS) is not an LPV most likely because terrain or obstacles are in the way of a 3 degree glide path so the step-down altitudes are retained. (see the forest of obstructions depicted near ZASBU; they may be the limiting factor in design of lower approaches to runway 2 at KSTS)  No vertical guidance is provided on approaches where the step-downs are required for terrain clearance.   If the receiver decided WAAS augmentation was unavailable the LP approach would become the LNAV approach and the higher MDA and visibility limits apply. 

 

Both approaches use WAAS in the sense that your 530W is using the WAAS GPS signals to augment GPS accuracy but only the LP approach is designed to make use of that enhanced accuracy.   There are no ground-based transmitters for WAAS; they are all installed on geosynchronous satellites. 

[golfpilot]

I'm over in Concord, I'll make my way over this week and fly the approaches with a 750 and get back to you if I get the same. 

[FlyDave]

I think the answer is

 

(1)  the non-precision approach (GPS 13 to KDVO)  is permitted to have an advisory glide slope (LNAV+V) calculated but it is still a non-precision approach and retains its (high) MDA.   According to Max Trescott, the FAA has found that the "Dive and Drive" step-down approaches are more dangerous than those where smooth descent is flown, hence the LNAV+V is built into GPS receiver databases when possible. 

 

There is  no LPV to KDVO because there is a hill in the way that blocks straight-in approaches and some more hills and towers on the missed approach path.  The MDA is about 1000' AGL, not a very low minimum. 

 

(2)  The precision approach you flew (LP to runway 2 at KSTS) is not an LPV most likely because terrain or obstacles are in the way of a 3 degree glide path so the step-down altitudes are retained. (see the forest of obstructions depicted near ZASBU; they may be the limiting factor in design of lower approaches to runway 2 at KSTS)  No vertical guidance is provided on approaches where the step-downs are required for terrain clearance.   If the receiver decided WAAS augmentation was unavailable the LP approach would become the LNAV approach and the higher MDA and visibility limits apply. 

 

Both approaches use WAAS in the sense that your 530W is using the WAAS GPS signals to augment GPS accuracy but only the LP approach is designed to make use of that enhanced accuracy.   There are no ground-based transmitters for WAAS; they are all installed on geosynchronous satellites. 

 

Jerry,

 

I agree with the assertion that a "Dive and Drive" approachs are more dangerous than an approach that provides "glideslope like" guidance.

Both approaches are non precision (LP is non-precision). The DVO approach doesn't list WAAS so I don't see how WAAS plays into the construction of this approach. I also didn't think you could have a glideslope without WAAS (Was I wrong again?).

Both approaches list step downs but the STS approach shows a step down that, if you are on the glideslope DEPTICTED on the approach plate (shown as a 3 degree angle/gliedslope) you should reach MDA before hitting the MAP - - could this have something to do with this issue. If so, why couldn't they flatten the "glideslope" to provide glideslope like guidance to an MDA (DA?) - just as on the DVO RWY 13 GPS approach.

I've had 2 glasses of wine (maybe 3.....) so I may be making sense to myself but no one else...Regardless - I don't think we're at the bottom of this TERPS conundrum!).

 

Dave

 

Dave

[NotarPilot]

Off topic but Dave, I appreciate how you write the name of the airport, VOR, etc in addition to the identifier.  Because if you only wrote the identifier of BFE like on some other threads I've read, I'd have no idea where that is.  

[Bob - S50]

I would just be guessing, but I don't think it has anything to do with WAAS.

 

My guess would be that the approach at STS has a stepdown fix at ZASBU before you get to the MAP so no vertical guidance is provided.  However, there is no stepdown fix between the FAF and MAP at DVO so it provided the artificial GS.

 

Again, just  a guess.  I don't have a 530 in my plane so I don't have a manual to look it up.

 

Bob

[midlifeflyer]

Jerry,

 

I agree with the assertion that a "Dive and Drive" approachs are more dangerous than an approach that provides "glideslope like" guidance.

Both approaches are non precision (LP is non-precision). The DVO approach doesn't list WAAS so I don't see how WAAS plays into the construction of this approach. I also didn't think you could have a glideslope without WAAS (Was I wrong again?).

 

Might be the wine but I'm not sure I understand.

 

It's WAAS that adds the information that calculates the advisory glideslope on an LNAV approach as well as the approved vertical guidance on LPV and LNAV/VNAV).  There's no advisory glideslope on an LP approach - that was intentional, the FAA wanting to ensure that one did not confuse LP (lateral guidance only) with LPV (lateral and vertical guidance). I guess the same issue potentially exists with respect to LNAV approaches. I'm guessing the FAA was a bit less worried about confusing a lateral-only approach (LP or LNAV) with a reg-certified lateral+vertical approach (LPV or LNAV/VNAV) than with confusing a lateral-only approach (LNAV) with a lateral-only approach (LNAV). [Note: LNAV+V is an annunciation from the unit, not a reference on an approach chart]

 

The bad news is the confusion exhibited by pilots, including those who fly with these systems.

 

There is, btw, a fairly decent description of all this from the FAA: RNAV (GPS) Approaches

 

Of course, since I really didn't understand my answer might make no sense  

[1964-M20E]

Me thinks that the FAA needs to revisit the whole precision GPS approach.

 

Assign only two types  precision and non precision and be done with it.  Either you have the capability to fly the GS or you do not. 

 

Why make things more complicated than they need to be (LPV, LNAV, VNAV)?  The ILS approach is straight forward and simple.  When you have the LOC and the GS you can go to X feet if you do not get the GS you fly the LOC approach and go to Y feet and you are done.  It is simple easy and no confusion.

 

I know I may oversimplify it but that seems to be what the  whole thread is about.

[Danb]

I actually do not think this is complicated, over-thinking the approach may be though.. As mid-lifeflyer stated in  his response  some of the info is supplementary as  he pointed out in the FAA circular on RNAV approaches, these questions a good in regard that it keeps us alert in  looking for the answers...

[FlyDave]

Off topic but Dave, I appreciate how you write the name of the airport, VOR, etc in addition to the identifier.  Because if you only wrote the identifier of BFE like on some other threads I've read, I'd have no idea where that is.  

Well, I think that's somewhere in Egypt...is it not?

[FlyDave]

So, I think I've found some of the info for an answer in this article:

 

http://flywhatsnext.com/resources/dyn/files/395131z5b17547b/_fn/gpsverticalguidance.pdf

 

Specifically - and as Jerry stated:

 

---------------------------------------

Some WAAS-enabled GPS UNITS provide advisory vertical guidance in association with GPS approaches. The LNAV+V notation is simply the
equipment manufacturer’s term for a GPS approach that includes an artificially created advisory glide path from the final approach fix to the touchdown point on the runway. The advisory glide path can provide a stabilized approach and eliminate the need for “dive and drive” descent to the MDA, but you need to understand clearly that an approach with the LNAV+V notation is not the same as LNAV/ VNAV or LPV (see below).

---------------------------------------

 

So I think part of the issue is that the glideslope provided on the GPS RWY 13 approach at KDVO may take you right to the touchdown point on the runway - Jerry, can you confirm this?

But still, the GPS RWY 13 approach at KDVO is not an LNAV+V, LNAV/VNAV or LPV approach as listed in the approach description at the top or in the minima at the bottom of the plate.

So again, anyone have any ideas as to why we'd get an advisory glideslope on an approach that is listed as a GPS RWY XX approach (final approach course must be withing 30 degrees of the runway heading) but no reference to Lateral or Vertical guidance (LP, LNAV, LNAV+V)?

[Bob - S50]

Me thinks that the FAA needs to revisit the whole precision GPS approach.

 

Assign only two types  precision and non precision and be done with it.  Either you have the capability to fly the GS or you do not. 

 

Why make things more complicated than they need to be (LPV, LNAV, VNAV)?  The ILS approach is straight forward and simple.  When you have the LOC and the GS you can go to X feet if you do not get the GS you fly the LOC approach and go to Y feet and you are done.  It is simple easy and no confusion.

 

I know I may oversimplify it but that seems to be what the  whole thread is about.

I think they do that because some planes fly LNAV, VNAV without a GPS.  The 757 and 767 I fly for example.  Most but not all have a GPS but the plane isn't actually using the GPS for navigation.  All it is doing is keeping the Inertial system updated on actual position.  Those without a GPS use DME/DME updating of position.  The LNAV, VNAV, and RNP approachs are flown based on position provided by the inertial system to the flight management computer.

 

So in my 757/767 I can fly LNAV, VNAV and RNP but not LPV approaches.  In my Mooney I can fly LNAV, VNAV and LPV approaches but not RNP approaches.

 

Bob

[flyboy0681]

I think they do that because some planes fly LNAV, VNAV without a GPS.  The 757 and 767 I fly for example.  Most but not all have a GPS but the plane isn't actually using the GPS for navigation.  

 

I know that both systems are on par with each other, but which system is "more" accurate, Inertial Reference or GPS?

[yvesg]

I know that both systems are on par with each other, but which system is "more" accurate, Inertial Reference or GPS?

If Inertial is updated by GPS like Bob said, then it cannot be more accurate than GPS... it would slowly get worse as the time lapses right Bob?

Yves

[kortopates]

So, I think I've found some of the info for an answer in this article:

 

http://flywhatsnext.com/resources/dyn/files/395131z5b17547b/_fn/gpsverticalguidance.pdf

 

Specifically - and as Jerry stated:

 

---------------------------------------

Some WAAS-enabled GPS UNITS provide advisory vertical guidance in association with GPS approaches. The LNAV+V notation is simply the

equipment manufacturer’s term for a GPS approach that includes an artificially created advisory glide path from the final approach fix to the touchdown point on the runway. The advisory glide path can provide a stabilized approach and eliminate the need for “dive and drive” descent to the MDA, but you need to understand clearly that an approach with the LNAV+V notation is not the same as LNAV/ VNAV or LPV (see below).

---------------------------------------

 

So I think part of the issue is that the glideslope provided on the GPS RWY 13 approach at KDVO may take you right to the touchdown point on the runway - Jerry, can you confirm this?

But still, the GPS RWY 13 approach at KDVO is not an LNAV+V, LNAV/VNAV or LPV approach as listed in the approach description at the top or in the minima at the bottom of the plate.

So again, anyone have any ideas as to why we'd get an advisory glideslope on an approach that is listed as a GPS RWY XX approach (final approach course must be withing 30 degrees of the runway heading) but no reference to Lateral or Vertical guidance (LP, LNAV, LNAV+V)?

 

I am not sure where your confusion lies since after Jerry answered your question, you quote the answer above and then ask for an explanation. So I'll offer a couple points that may or may not help as it sounds like the concept of an "advisory glide slope" is new to you.

- Most importantly an "advisory glide slope", referred to as the +V in LNAV+V, can only be used to MDA - you can not follow it below MDA to the threshold. The calculated glide slope is there only to help you fly from final to MDA (including in a continuous descent when there are intermediate points)

- There no such thing as "LNAV+V" approach minimums, it is merely a LNAV approach that when flown by a WAAS GPS navigator, the box calculates an advisory glide slope to enable a continuous descent to get to the MDA. Fly it with a non-waas GPS and of course you will not get the +V advisory glide slope.

- Advisory Glide slopes if miss understood can be dangerous. Some pilots don't understand the difference and could end up following it below MDA where terrain or obstructions are an issue.

- Unlike NOAA, Jeppesen shows the details of the +V slope so you have an accurate picture of where it goes. I've attached the Jepp chart version of both of these, but see the DVO one in particular since it plots the +V glide slope and clearly shows that it will arrive at the MDA well before the MAP at GOVLE - cautioning you not to descent below MDA until you have a required element of the runway environment in sight.

 

As to the question of why you don't have an advisory glide slope on the STS GPS2 approach - there could be many reasons. For example when the required glide slope is not co-incident with the vertical glide slope, the FAA has been pulling the +V glide slope off the plates for LNAV and LP approaches. I don't see a issue with the chart though and would expect to see a +V glide slope. However, there may be another reason due to your software. Originally when Garmin introduced LP approaches they did so without an advisory glide slope, sighting the FAA required them too for approval. They got a lot of hate mail for that since almost always the LP approach was added to an existing LNAV approach that previously had +V. They were initially giving us new LP approaches at the cost of removing the +V on the original LNAV approach - not good!   (since you are loading the same approach regardless if you are flying to LP or LNAV minimums). But finally just around the beginning of the year, Garmin released s/w ver 5.1 to add +V back to LP and hence LNAV approaches co-located with LP. S/w 5.1  also brought back many approaches that had been disabled by the Garmin s/w after the FAA changed the +V glide slope to 0 in an effort to disable to downgrade many LNAV approaches based on some new criteria to make them safer.

 

So in short, check the s/w ver of your GPS and if it doesn't have the recent update from this year (ver 5.1) I'd expect the upgrade will provide +V on the STS GPS2 approach. 

 

Lastly, if the concept of +V used in LNAV and LP versus LNAV/VNAV  and LPV are not clearly understood, read you Garmin documentation and other literature and talk to your CFII till you understand the differences and most importantly their limitations.

DVO GPS13.pdf

KSTS GPS2.pdf

[midlifeflyer]

Me thinks that the FAA needs to revisit the whole precision GPS approach.

 

Assign only two types  precision and non precision and be done with it.  Either you have the capability to fly the GS or you do not. 

 

Why make things more complicated than they need to be (LPV, LNAV, VNAV)?  The ILS approach is straight forward and simple.  When you have the LOC and the GS you can go to X feet if you do not get the GS you fly the LOC approach and go to Y feet and you are done.  It is simple easy and no confusion.

 

I know I may oversimplify it but that seems to be what the  whole thread is about.

 

I think you forgot somehting that appears on some LOC (and VOR) approaches. Are you suggesting getting rid of DME stepdown fixes that serve to reduce minimums? Perhaps make all of them with (a) higher minimums so all can fly them or (b ) NA for anyone without DME capability?

 

Just like the DME stepdown situation, the best simplification is understanding your equipment. It's been said that there's a trade-off for the simplicity of actually flying a GPS approach - complexity in the set up. Add to that the complexity of understanding the capabilities and limitations of the equipment.

[FlyDave]

I am not sure where your confusion lies since after Jerry answered your question, you quote the answer above and then ask for an explanation. So I'll offer a couple points that may or may not help as it sounds like the concept of an "advisory glide slope" is new to you.

- Most importantly an "advisory glide slope", referred to as the +V in LNAV+V, can only be used to MDA - you can not follow it below MDA to the threshold. The calculated glide slope is there only to help you fly from final to MDA (including in a continuous descent when there are intermediate points)

- There no such thing as "LNAV+V" approach minimums, it is merely a LNAV approach that when flown by a WAAS GPS navigator, the box calculates an advisory glide slope to enable a continuous descent to get to the MDA. Fly it with a non-waas GPS and of course you will not get the +V advisory glide slope.

- Advisory Glide slopes if miss understood can be dangerous. Some pilots don't understand the difference and could end up following it below MDA where terrain or obstructions are an issue.

- Unlike NOAA, Jeppesen shows the details of the +V slope so you have an accurate picture of where it goes. I've attached the Jepp chart version of both of these, but see the DVO one in particular since it plots the +V glide slope and clearly shows that it will arrive at the MDA well before the MAP at GOVLE - cautioning you not to descent below MDA until you have a required element of the runway environment in sight.

 

As to the question of why you don't have an advisory glide slope on the STS GPS2 approach - there could be many reasons. For example when the required glide slope is not co-incident with the vertical glide slope, the FAA has been pulling the +V glide slope off the plates for LNAV and LP approaches. I don't see a issue with the chart though and would expect to see a +V glide slope. However, there may be another reason due to your software. Originally when Garmin introduced LP approaches they did so without an advisory glide slope, sighting the FAA required them too for approval. They got a lot of hate mail for that since almost always the LP approach was added to an existing LNAV approach that previously had +V. They were initially giving us new LP approaches at the cost of removing the +V on the original LNAV approach - not good!   (since you are loading the same approach regardless if you are flying to LP or LNAV minimums). But finally just around the beginning of the year, Garmin released s/w ver 5.1 to add +V back to LP and hence LNAV approaches co-located with LP. S/w 5.1  also brought back many approaches that had been disabled by the Garmin s/w after the FAA changed the +V glide slope to 0 in an effort to disable to downgrade many LNAV approaches based on some new criteria to make them safer.

 

So in short, check the s/w ver of your GPS and if it doesn't have the recent update from this year (ver 5.1) I'd expect the upgrade will provide +V on the STS GPS2 approach. 

 

Lastly, if the concept of +V used in LNAV and LP versus LNAV/VNAV  and LPV are not clearly understood, read you Garmin documentation and other literature and talk to your CFII till you understand the differences and most importantly their limitations.

 

Paul,

 

Thanks for the explanations.

Yes, I do understand the concepts of the different types of GPS approaches and I know that a glideslope is only intended to get you to DA and no lower. I'm afraid the SW on my 530W is old so I'll look into getting that updated.

My last question was in regard to getting an advisory glideslope on an approach  that is listed as a GPS approach (GPS RWY 13 at KDVO) but is not listed as utilizing WAAS and is not an LP, LNAV, LNAV+V, etc. approach. A SW update on my 530W may get me an advisory glideslope on the RNAV (GPS) RWY 12 at KSTS but I'm still a little confused as to why we get the advisory glideslope on the GPS RWY 13 at DVO approach. There doesn't seem to be consistency in the generation of these advisory glideslopes by the 530W. What am I missing here?

 

Dave

[kortopates]

Paul,

 

Thanks for the explanations.

Yes, I do understand the concepts of the different types of GPS approaches and I know that a glideslope is only intended to get you to DA and no lower. I'm afraid the SW on my 530W is old so I'll look into getting that updated.

My last question was in regard to getting an advisory glideslope on an approach  that is listed as a GPS approach (GPS RWY 13 at KDVO) but is not listed as utilizing WAAS and is not an LP, LNAV, LNAV+V, etc. approach. A SW update on my 530W may get me an advisory glideslope on the RNAV (GPS) RWY 12 at KSTS but I'm still a little confused as to why we get the advisory glideslope on the GPS RWY 13 at DVO approach. There doesn't seem to be consistency in the generation of these advisory glideslopes by the 530W. What am I missing something here?

 

Dave

 

Dave,

Why do we get Advisory Glide Slopes on the DVO GPS R13? 

 - The DVO GPS R13 is not a WAAS approach as you point out. Its is a LNAV approach. So where does the advisory glide slope come from? Unfortunately, the NOAA plate give us no clues, so look closely at the Jeppesen plate for DVO GPS13 in the profile view and the small table below it. You should see a dashed grey line come from the FAF labeled 3.66 degrees which is a plot of the VDA or Vertical Descent Angle that FAA TERPS'ers designed the approach too. When flown with a Garmin WAAS GPS, your GPS will use this VDA to provide you an advisory glide slope. It still an LNAV approach flown to LNAV minimums, but when flown with a WAAS GPS it is able to provide you with LNAV+V guidance - again it doesn't change the minimums and thus there are never LNAV+V minimums ever listed in an approach plate. 

The +V guidance provided by your WAAS GPS to a LNAV approach, making it a LNAV+V, is merely your box giving you a glide slope based on the charted or plotted VDA. So to fully understand VDA briefly review AIM 5-4-5 7 k. "Vertical Descent Angle (VDA) on Nonprecision Approaches."  (see https://www.faa.gov/air_traffic/publications/atpubs/aim/aim0504.html#BZbKz318mweb)%C2'> charted VDA is what Garmin is using. Note that the AIM also says "FAA policy is to publish VDAs on all nonprecision approaches." Well that was much more true a few years ago when Garmin started using the VDA to provide +V. Ever since the FAA has imposed additional criteria and been removing the charted VDA on many plates - most likely because many pilots treated the advisory glide slope like a precision approach. Obviously when removed you no longer have +V on a LNAV nor LP approach. But the AIM falls short in explaining all necessary criteria. But most recently, we've seen the FAA remove VDA's on approach charts where the VDP or VGSI are not coincident with the VDA - they say in paragraph 2 below K that they publish a note to that effect, but I can tell you they've been on a big campaign to remove the VDA entirely in this case and there could be more criteria to exclude it as well. But the AIM has not yet caught up with these latest changes and not being a TERPer I can only comment on the changes we've been seeing in recent years. You may notice the AIM only makes one mention of "advisory vertical guidance" in 5-4-5 m.1.(d) under LP approaches  "... WAAS avionics may provide GNSS-based advisory vertical guidance during an approach to an LP line of minima." Rather odd they don't mention advisory vertical guidance in LNAV approaches where we've had it for many years and only a make single reference to it in the newer LP approach without ever clarifying this is +V but for that you'd likely have to refer to the Garmin documentation.

 

So in sum, a VDA use to be available in most LNAV approaches and has been used to provide +V guidance in LNAV+V (and recently LP+V approaches with s/w ver 5.1). But the FAA has been removing the VDA's on many charts it previously included; such as when the VDA is not coincident with the VGSLI. So to know in advance if you can expect it, you really have to look at a Jepp chart because unlike NOAA, they include the VDA when charted by the FAA  and will provide you with a table as to what descent rate you use for your a given ground speed. 

Hope that helps. As you have noticed, NOAA publishes it sometimes...

[FlyDave]

Paul,

 

Thanks - you have provided an excellent explanation of a process that has been poorly implemented by the FAA/NOAA.

Not sure I'll be subscribing to Jepp plates but I will be getting my 530 updated.

 

Thanks again for an excellent explanation!

 

Dave

[kortopates]

Happy to help. You should find the s/w upgrade to be minimal cost; especially if you go to a shop that you already have a relationship with.

I dropped my two GPS's off at the shop and picked them up a little later. They didn't charge me for it and included a print out of the 20 to 30 page POH supplement to put in my POH. I then had it copied to a reduced double sided version to fit the supplement into my POH.