RNAV approach, LNAV Category, getting glide slope (LNAV+V)

texasag93

texasag93

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texasag93
We have a GTN 750 in the Bonanza.

We flew into 0F2 (Bowie, TX) RNAV RWY 17. It is a LNAV approach.

When we were on the approach, LNAV + V showed on the 750 and we got a glide slope.

2 weeks ago, we were flying into KLXY (Mexia, TX) RNAV 36. It is also a LNAV approach.

We did not get a glide slope. I did not look at the 750 that time, but with no glide slope indicator on the Aspen, I did the non precision approach decent.

Does anyone know how can I look and see ahead of time if the LNAV will give me the +V?

Thanks.
 
texasag93 said:
We have a GTN 750 in the Bonanza.

We flew into 0F2 (Bowie, TX) RNAV RWY 17. It is a LNAV approach.

When we were on the approach, LNAV + V showed on the 750 and we got a glide slope.

2 weeks ago, we were flying into KLXY (Mexia, TX) RNAV 36. It is also a LNAV approach.

We did not get a glide slope. I did not look at the 750 that time, but with no glide slope indicator on the Aspen, I did the non precision approach decent.

Does anyone know how can I look and see ahead of time if the LNAV will give me the +V?

Thanks.
Click to expand...

That's a good question. My guess is that if you see the glide slope angle specified on the approach plate, the GTN should give you the "advisory glide slope" ("+V").
Another ugly solution is to check it on the desktop trainer, which is relatively up to date, but not current.
But I'd like to hear from others.
 
This is from the Garmin blog, hope it is what you were looking for....

And how can we tell if an LNAV approach will have the +V? First of all, if an approach has the LPV or LNAV/VNAV minimum the system will prefer these types as they will get you lower on the approach so LNAV+V will not be available. For straight LNAV approaches you can tell whether you will receive the +V when you load or activate the approach. In the GNS 430W/530W series units the LNAV+V will be in the procedures pages at the bottom when loading or activating the approach. In the GTN 750/650 series units the label of +V will not appear until the approach is loaded into the flight plan and then it will show in the title of the approach. G1000 systems will also display the +V in the title of the approach on the flight plan.
 
I have a GTN 650. LNAV +V is still an LNAV approach flown to LNAV minimums. The glide path (technically not a glider slope) is advisory only as it is generated by the GTN and not part of the approach database.
 
tsts4 said:
I have a GTN 650. LNAV +V is still an LNAV approach flown to LNAV minimums. The glide path (technically not a glider slope) is advisory only as it is generated by the GTN and not part of the approach database.
Click to expand...
Absolutely true and you also need to meet any step-down minimums along the way.

But based on the examples, I don't think it answers the OP's questions which comes down to (1) "why does the GTN generate an advisory glidepath for some LNAV-only approaches and not for others?" and (2) "is there a way I can tell in advance?"

I suspect if there is a rhyme and reason to answer #1, it probably furnished the answer to #2.
 
0F2 RNAV (GPS) RWY 17 has LNAV minimums only.
KLXY RNAV (GPS) RWY 36 has LP and LNAV minimums. The MDA for the LP approach is 20 feet lower than for the LNAV approach. There is also a noticeable difference in AGL numbers for the minimums here (LP 319, LNAV 339) compared with those at 0F2 (539).

Any other differences between these two approaches? Does anyone know how the decision is made to offer an LP or only LNAV? It doesn't seem to make sense to provide vertical guidance for LNAV but not for LP. Maybe the GTN 750 gives vertical guidance when the minimums are higher off the ground but not when they are lower?
 
iamtheari said:
0F2 RNAV (GPS) RWY 17 has LNAV minimums only.
KLXY RNAV (GPS) RWY 36 has LP and LNAV minimums. The MDA for the LP approach is 20 feet lower than for the LNAV approach. There is also a noticeable difference in AGL numbers for the minimums here (LP 319, LNAV 339) compared with those at 0F2 (539).

Any other differences between these two approaches?
Click to expand...
Yes. A big one. Look at the grey line that continues from the MDA to the runway on the 0F2 approach profile view. That means a lack of obstacles on the visual segment from the MDA to the runway on a 34:1 glide path. That is not there on the KLXY approach, indicating that it has not been certified to be clear of obstacles.

That might have something to do with the willingness of Garimin to provide an LNAV+V advisory glidepath for one and not for the other.
 
texasag93 said:
We have a GTN 750 in the Bonanza.

We flew into 0F2 (Bowie, TX) RNAV RWY 17. It is a LNAV approach.

When we were on the approach, LNAV + V showed on the 750 and we got a glide slope.

2 weeks ago, we were flying into KLXY (Mexia, TX) RNAV 36. It is also a LNAV approach.

We did not get a glide slope. I did not look at the 750 that time, but with no glide slope indicator on the Aspen, I did the non precision approach decent.

Does anyone know how can I look and see ahead of time if the LNAV will give me the +V?

Thanks.
Click to expand...

You should be able to determine by loading the airport, then reviewing the approaches without actually loading them:


0F2
RNAV GPS 17
LNAV +V

KLXY
RNAV GPS 36
LP +V
 
aterpster said:
You should be able to determine by loading the airport, then reviewing the approaches without actually loading them:

0F2
RNAV GPS 17
LNAV +V

KLXY
RNAV GPS 36
LP +V
Click to expand...

Yes, but what if you are at home?
As I noted above, the only way I know of predicting the availability of +V is to look for a published descent angle and/or find it on the desktop trainer.
Not sure which is more reliable or easier, and neither is foolproof. It would be much nicer to have reliable data published online somewhere.
 
aterpster said:
You should be able to determine by loading the airport, then reviewing the approaches without actually loading them:
Click to expand...
I guess the question (mine if not his), @Wally (I hoped you'd join this discussion), is, is there some standard the GPS manufacturers use to decide whether an lateral RNAV approach gets advisory vertical guidance? Is there something on the approach plate and nothing else that gives us a clue?
 
midlifeflyer said:
Yes. A big one. Look at the grey line that continues from the MDA to the runway on the 0F2 approach profile view. That means a lack of obstacles on the visual segment from the MDA to the runway on a 34:1 glide path. That is not there on the KLXY approach, indicating that it has not been certified to be clear of obstacles.

That might have something to do with the willingness of Garimin to provide an LNAV+V advisory glidepath for one and not for the other.
Click to expand...

My guess is that is it. VGSI not being coincident probably figures in also. I'm assuming they are guarding against pilots being lead down the "primrose path" by over reliance on the +V advisory glidethingy.
 
midlifeflyer said:
I guess the question (mine if not his), @Wally (I hoped you'd join this discussion), is, is there some standard the GPS manufacturers use to decide whether an lateral RNAV approach gets advisory vertical guidance? Is there something on the approach plate and nothing else that gives us a clue?
Click to expand...
Until recently, if there was no VDA there would be no +V advisory path, but that policy seems to now be in a state of flux at the FAA. The only 100% method is what I mentioned previously.

I suppose outside of the airplane looking at the NDBR source on the FAA's IFP gateway would be close to 100%, but that seems rather arduous.
 
aterpster said:
Until recently, if there was no VDA there would be no +V advisory path, but that policy seems to now be in a state of flux at the FAA. The only 100% method is what I mentioned previously.

I suppose outside of the airplane looking at the NDBR source on the FAA's IFP gateway would be close to 100%, but that seems rather arduous.
Click to expand...
Thanks Wally.

Fortunately it is mostly an academic exercise. Finding out during the approach briefing should be enough.
 
Last edited:
I was searching for something once and got a "Terps" site. Wally rings a bell. Is that you?
 
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