LNAV vs LP approaches?

[Let'sgoflying!]

I was reading about the differences between LNAV & LP approaches; the author said they are basically the same - lateral guidance with advisory glideslope.
He showed two approaches to the same runway in Idaho, the LNAV with the much higher ceiling minima, and an LP with lower ceiling minima.
The LP required WAAS, which gave it better ‘accuracy’.
Does the FAA keep the LNAV approaches active for those with non-waas receivers?
Or is it because of ground-based waas tower outages?
Are there plans to phase out LNAV approaches?

 

[RussR]

There are no plans to phase out LNAV approaches. Yes the LNAV approaches are there in cases of either degraded WAAS accuracy, or for aircraft that are not equipped with WAAS.

 

[bentmettle]

Did the article also happen to reiterate that the lateral guidance functions differently between the two? Fixed lateral guidance vs angular guidance?

 

[MauleSkinner]

There are no plans to phase out LNAV approaches. Yes the LNAV approaches are there in cases of either degraded WAAS accuracy, or for aircraft that are not equipped with WAAS.

And it’s not JUST a WAAS requirement…there are WAAS boxes out there that were certified before LP existed, so they still can’t do LP minimums.

 

[bentmettle]

The AIM has some good discussion on LP vs LPV. I’m on the tail end of instrument checkride prep and wish I’d just read the AIM more in some cases vs other secondary sources. And the price is right.

 

[Clip4]

I was reading about the differences between LNAV & LP approaches; the author said they are basically the same - lateral guidance with advisory glideslope.
He showed two approaches to the same runway in Idaho, the LNAV with the much higher ceiling minima, and an LP with lower ceiling minima.
The LP required WAAS, which gave it better ‘accuracy’.
Does the FAA keep the LNAV approaches active for those with non-waas receivers?
Or is it because of ground-based waas tower outages?
Are there plans to phase out LNAV approaches?

Not quite. LP=Localizer performance and requires WAAS. This means accuracy of the approach is greater than an LNAV. There is not advisory glide slope on an LP. You may get LNAV+P with WAAS.

 

[midlifeflyer]

The AIM has some good discussion on LP vs LPV. I’m on the tail end of instrument checkride prep and wish I’d just read the AIM more in some cases vs other secondary sources. And the price is right.

The AIM gets dissed and sometimes completely ignored because of that “not regulatory” nonsense. But it is really a mine of information.

 

[robin ardoin]

And it’s not JUST a WAAS requirement…there are WAAS boxes out there that were certified before LP existed, so they still can’t do LP minimums.

Learned something new...thanks. I assumed all WAAS were LP capable.

 

[midlifeflyer]

There is not advisory glide slope on an LP.

 

[Brad Z]

View attachment 129048

Interesting, because LP approaches are the result of surveys that did not support an LPV approach, due to some sort of surface area penetration. Vertical guidance on an LP approach may get you closer to terrain or obstructions than you like. Use with caution, particularly in the visual segment of the approach.

 

[tsts4]

Use with caution, particularly in the visual segment of the approach.

I think that's sound advice for any of the +V approaches where the box generates an advisory GP. Caution also applies to MDAs and step-downs too.

 

[midlifeflyer]

Interesting, because LP approaches are the result of surveys that did not support an LPV approach, due to some sort of surface area penetration. Vertical guidance on an LP approach may get you closer to terrain or obstructions than you like. Use with caution, particularly in the visual segment of the approach.

As @tsts4 said, that applies to all +V, including (doncha just LOVE it?)…



Where you don’t see it is LOC approaches but that may just be because you are not suppose to do primary GPS in LOC even with raw data displayed elsewhere.

 

[midlifeflyer]

Interesting, because LP approaches are the result of surveys that did not support an LPV approach, due to some sort of surface area penetration. Vertical guidance on an LP approach may get you closer to terrain or obstructions than you like. Use with caution, particularly in the visual segment of the approach.

BTW, on that approach I often have the pilot pull the hood off early. The 34:1 visual segment is definitely not clear.

 

[455 Bravo Uniform]

You may get LNAV+P with WAAS.

I think you meant LNAV+V? +P is for 9mm and “stuff” like that…

 

[Ventucky Red]

Can you share the article with us?

 

[MauleSkinner]

I think you meant LNAV+V? +P is for 9mm and “stuff” like that…

Maybe the +P is what happens when you see the terrain or obstructions in the visual segment.

 

[Let'sgoflying!]

Can you share the article with us?

 

[bentmettle]

Thanks for sharing that video. It's good they showed the guidance differences. It's probably secondary to what they wanted to show, but you wouldn't pick the approach based on your GPS, you'd pick your approach on your ability to fly the required climb gradient to fly the missed. So I guess I'd pick at that scab a bit- you don't shop for your MDA or approach strictly based on nav equipment, you also have to know your climbout capability.

And, indeed, if you pull the plates for their example approaches, the notes for the Zulu approach says

Missed approach requires minimum climb of 318 feet per NM to 4500 if unable to meet climb gradient, see RNAV (GPS) Y RWY 20.

 

[chemgeek]

I think that's sound advice for any of the +V approaches where the box generates an advisory GP. Caution also applies to MDAs and step-downs too.

Absolutely. Terrain clearance beyond below the DA is not assured when using advisory vertical guidance. The magic box will let you fly the vertical guidance right into the ground. This is one reason I "dive and drive" on LNAV approaches. (It also gets you out of the bases quicker if conditions are not at minimums.)