Garmin 430W and LPV vs. VNAV/LNAV

oktex88

oktex88

Well-Known Member
Lets say I want to fly a GPS approaching using the Garmin 430W and it has LPV mins published. What if for some reason I just wanted to fly the GPS the old school way using only LNAV is there a way to set up the GPS to do this? I know yes I could just ignore the glideslope indications but what if I wanted to use the autopilot on the approach? It would follow the glideslope.

Also what is the difference between LPV and VNAV/LNAV on GPS approaches?
 
oktex88 said:
Lets say I want to fly a GPS approaching using the Garmin 430W and it has LPV mins published. What if for some reason I just wanted to fly the GPS the old school way using only LNAV is there a way to set up the GPS to do this? I know yes I could just ignore the glideslope indications but what if I wanted to use the autopilot on the approach? It would follow the glideslope.

Also what is the difference between LPV and VNAV/LNAV on GPS approaches?
Click to expand...
Aux > SBAS > turn off WAAS.

and you can make it so it won't intercept the GS. just press either alt or apr mode twice. i would have to play with it a little to remember exactly how.
 
deadstick said:
They offer a lower mins because the system gets more sensitive (like a LOC) the closer you get.
Click to expand...
Do you have any better sources on this?

The best I have is on page 272 of the IPH

Instrument Procedures handbook page 272 said:
Approaching the runway, a LPV nominal 3 degrees glidepath starts
out linear (±150 M FSD) and then approximately 6 NM from the
landing threshold becomes angular at a width of ±0.75 degrees
and then becomes linear again as early as approximately 1.9 NM
from the GPI for a ±45 M FSD or as small as a ±15 M FSD at a
distance of approximately 0.6 NM from the landing threshold
(depending on the manufacturer).
Click to expand...

I would love a graphic explanation if anyone has one
 
bdhill1979 said:
Do you have any better sources on this?

The best I have is on page 272 of the IPH



I would love a graphic explanation if anyone has one
Click to expand...


The graphic on p35 kind of supports the IPH quote you had.

I think the RNPs are 5,2, and .3 for ENR, TERM, and APR. When you cross the 30 and 2 nm distances, the system "ramps down" to the next lowest level. It's not instantaneous. The same happens with the LPV it ramps down to a lower value for full deflection -- in other words, the closer you are the more sensitie it becomes. Otherwise, when it went from TERM to APR, the needle would go from 1/4 deflection to full. Also, the name: LPV=Localizer Performance with Vertical guidance. In a GPS appraoch (LNAV only) that RNP remains unchanged. At the MAP, doesn't it go back to TERM?
 
deadstick said:
The graphic on p35 kind of supports the IPH quote you had.

I think the RNPs are 5,2, and .3 for ENR, TERM, and APR. When you cross the 30 and 2 nm distances, the system "ramps down" to the next lowest level. It's not instantaneous. The same happens with the LPV it ramps down to a lower value for full deflection -- in other words, the closer you are the more sensitie it becomes. Otherwise, when it went from TERM to APR, the needle would go from 1/4 deflection to full. Also, the name: LPV=Localizer Performance with Vertical guidance. In a GPS appraoch (LNAV only) that RNP remains unchanged. At the MAP, doesn't it go back to TERM?
Click to expand...

I was referring to the vertical scaling on an LPV approach, I have not seen that adequately (or should I say simply) explained anywhere. The RNP levels are actually 2 for ENR (it used to be 5 in older publications, or maybe that is based on GPS manufacturer), 1 for TERM, and .3 for APR. That stuff is really well explained and graphed, but I have a hard time explaining how the vertical guidance of the LPV glide path scales.
 
bdhill1979 said:
I was referring to the vertical scaling on an LPV approach, I have not seen that adequately (or should I say simply) explained anywhere. The RNP levels are actually 2 for ENR (it used to be 5 in older publications, or maybe that is based on GPS manufacturer), 1 for TERM, and .3 for APR. That stuff is really well explained and graphed, but I have a hard time explaining how the vertical guidance of the LPV glide path scales.
Click to expand...

I missed the memo on the ENR since my KLN94 days, and I had the "2" on my mind for the 2nm from FAF. Oh well.

As for the vertical nav, I was JUST going over this in the ever-exciting, the thrilling FIRC. This is all that's said about the vertical guidance:
"Use a database-derived glide path that can be flown to a DA that has similar minimums to an ILS." Is it just connecting a bunch of dots?
 
deadstick said:
I missed the memo on the ENR since my KLN94 days, and I had the "2" on my mind for the 2nm from FAF. Oh well.

As for the vertical nav, I was JUST going over this in the ever-exciting, the thrilling FIRC. This is all that's said about the vertical guidance:
"Use a database-derived glide path that can be flown to a DA that has similar minimums to an ILS." Is it just connecting a bunch of dots?
Click to expand...
See that is exactly my question. I know it does it, but how, and how do I teach that. That excerpt I posted from the IPH was the best I had up until what you posted, and that helps, but still doesn't make it clear enough to put into a students brain. In fact I really don't even teach it because I am so un-confident of what it is I would be teaching. Just that the GP exists within the database. Yet I expect them to understand the course width and height of an ILS and the how and why it becomes more sensitive.

LPV is our future, so I would love to be able to adequately explain and teach.
 
To add to this conversation, is it legal to fly a GPS approach without an operating CDI? In other words, can you zoom way in to the GPS NAV page and just use your cross-track error for lateral guidance on an LNAV only approach?
 
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