Garmin 430W RNAV Approach Question

HF17

HF17

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HF17
When shooting an RNAV approach, why does the GPS sometimes say “L/VNAV” instead of always saying “LPV?” I understand that different minimums are used, but is it because not enough satellites are in view to be able to do an LPV approach? If so, how many satellites are required for each type of RNAV approach?


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Not enough details here. Some approaches do not have LPV minimums. Your reception might be bad, or any other number of things.

What airports/approaches?
 
Not enough information to answer the question. Assuming there is good WAAS integrity, then:

If there are LPV minimums, the unit should annunciate LPV.
If the top line of minimums is LNAV/VNAV, then it should say "L/VNAV".
If there are only LNAV minimums, then you will often see "LNAV+V", for LNAV with an advisory glidepath.

If there is not good WAAS integrity, then the unit should give you a warning and downgrade straight to LNAV. It will not downgrade from LPV to LNAV/VNAV, since both require WAAS for the glidepath.

If you can give specific approach examples, that would help.
 
RussR said:
Not enough information to answer the question. Assuming there is good WAAS integrity, then:

If there are LPV minimums, the unit should annunciate LPV.
If the top line of minimums is LNAV/VNAV, then it should say "L/VNAV".
If there are only LNAV minimums, then you will often see "LNAV+V", for LNAV with an advisory glidepath.

If there is not good WAAS integrity, then the unit should give you a warning and downgrade straight to LNAV. It will not downgrade from LPV to LNAV/VNAV, since both require WAAS for the glidepath.

If you can give specific approach examples, that would help.
Click to expand...

What would cause poor WAAS integrity? Would it be from the conditions of the Ionosphere?


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Could be signal integrity, could just be the LPV approach isn’t in the data base.
 
As others have said...you need to provide more information...like the approach name and whether you experienced an outage. It could just be the specific approach only allows for LNAV/VNAV minimums in which case that's all you're going to get.

If you're really asking why all the different rnav approaches and minima, then you may want to clarify.
 
FYI, if there is a vertical guidance circuit board failure in the GNS430W it will simply not arm LPV approaches, but rather downgrade to LNAV, with no obvious warning of the failure. This happened to my GNS-430W, and it took me couple of approaches to figure out it was the unit, and not the GPS signal at fault. The GNS-430W will normally arm LPV if available and the box is operating correctly.
 
HF17 said:
When shooting an RNAV approach, why does the GPS sometimes say “L/VNAV” instead of always saying “LPV?” I understand that different minimums are used, but is it because not enough satellites are in view to be able to do an LPV approach? If so, how many satellites are required for each type of RNAV approach?
Click to expand...

I doubt you ever saw L/VNAV as an annunciation. It does occur, but at so few airports, it is a rarity. Since you have chosen not to identify the airport and the approach, I am guessing you can't name one. It will only occur at an airport with an approach that does have a LNAV/VNAV line of minimums and does not have an LPV line of minimums.
 
John Collins said:
I doubt you ever saw L/VNAV as an annunciation. It does occur, but at so few airports, it is a rarity. Since you have chosen not to identify the airport and the approach, I am guessing you can't name one. It will only occur at an airport with an approach that does have a LNAV/VNAV line of minimums and does not have an LPV line of minimums.
Click to expand...
Yes. That's true even if the LNAV/VNAV minimums are lower than LPV.
 
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