LNAV approach with 430 WAAS

[Bavafa]

Can any one here help me out to understand these approach a bit better?

My understanding of LNAV is that only lateral guidance is provided by the GPS but I have flown a number of LNAV approach that I also get the vertical guidance. Does any one know how this works?

Also, is there any other difference between LPV and LNAV+V beside the facts that minimums are lower for LPV?

Thanks in advance

[TCONROY]

LNAV: A non-precision GPS approach with only lateral guidance. The approach will have altitude step-downs with an MDA.

LNAV + V: This non-precision approach has an extra feature in that the glideslope needle comes alive. This gives you a stabilized approach, but does not give you obstacle clearance. The glideslope portion is added by Jeppesen and keeps you at or above any published step-downs.

LNAV/VNAV—or L/VNAV: This approach gives you lateral and vertical guidance down the final approach course. This is not a precision approach like an ILS, but you are assured of clearance above terrain and obstacles. Fly it like a precision approach, and trust the increased decision heights to compensate for the lower accuracy of a precision approach.

LPV: This is the most accurate WAAS approach, giving you lateral and vertical guidance to decision altitudes as low as 200 feet agl. On an LPV approach, accuracy is 16 meters laterally, and four meters vertically. The terrain and obstacle clearance zone is that of a Cat 1 ILS approach.

[Radomir]

The shortest yet easiest to understand explanation is here:

http://garmin.blogs.com/my_weblog/20...-runway-c.html


There are other resources that go more in depth, but the above will be sufficient for most folks..

[Bavafa]

Originally Posted by TCONROY

LNAV: A non-precision GPS approach with only lateral guidance. The approach will have altitude step-downs with an MDA.

The part that has confused me is that most LNAV approach I have made, my glideslop needle has become active and provided vertical guidance. I am wondering where is this coming from, how it works and what causes it to come alive or NOT.

My home airport KPVF has a LNAV approach and I have always got the vertical guidance in this approach.

BTW, a very good and complete explanation of all type of GPS approach

[TCONROY]

You might check your GNS-430W during that approach again. It will probably say LNAV+V which means you use LNAV minimums shown on the chart but the GNS-430W is giving you an advisory glideslope only.

[Bavafa]

Originally Posted by TCONROY

You might check your GNS-430W during that approach again. It will probably say LNAV+V which means you use LNAV minimums shown on the chart but the GNS-430W is giving you an advisory glideslope only.

Good point and I will test it on my next approach. Much appreciate the very good, logical and useful info.

[pierre smith]

...that vertical guidance is available either. This happened recently at KOKZ. My buddy runs the FBO there and told me that they had VNAV now, so the next time I flew over, I loaded the approach in the 430W and...son-of-a-gun---glideslope bar! The added benefit was ahead of printing the approach.

Best,

[DGlaeser]

Originally Posted by pierre smith

...that vertical guidance is available either. This happened recently at KOKZ. My buddy runs the FBO there and told me that they had VNAV now, so the next time I flew over, I loaded the approach in the 430W and...son-of-a-gun---glideslope bar! The added benefit was ahead of printing the approach.
Best,

I don't know what the criteria are for showing VNAV on the approach charts, but I've seen quite a few, including the airport where I instruct, that have had LNAV+V for a while (many chart cycles) but it is not shown on the chart.
You don't have to wait to see a glide slope - the approach name in the GPS will tell you.

[pierre smith]

...if I'm planning on a cross-country and the weather is forecast to remain 500 overcast and the LNAV DA is 800', I'm not going.

If the approach has a published VNAV or LPV and the minimums are below that 500', I'd feel much better going on the trip. I can only safely go by what the approach charts have published, not guessing that they might have vertical guidance when I get there.

Best,

[Radomir]

The +V guidance is not legal and cannot be used towards lower minimums.. so it's irrelevant if it's there or not.. Sure helps if it's there, but legally speaking it doesn't matter. You'll never see +V on approach plates.