LPV approaches

[AlanM]

Hello. I've been searching through the AIM to find out if an LVP approach is TECHNICALLY considered a precision or non-precision approach. Does anyone have the answer that is evading me?

Also, I fly a C172SP w/ a G1000 avionics suite EXCEPT FOR the autopilot, which is a KAP 140. My instructor and I have yet to prove this to me, but he is stating that because the autopilot is NOT integrated into the G1000 system, it will not fly the LPV glide path. Is he correct?

Thanks to all.

 

[Speed]

From a few years ago...

http://www.pilotsofamerica.com/forum/showthread.php?t=14708

 

[Velocity173]

Hello. I've been searching through the AIM to find out if an LVP approach is TECHNICALLY considered a precision or non-precision approach. Does anyone have the answer that is evading me?

Also, I fly a C172SP w/ a G1000 avionics suite EXCEPT FOR the autopilot, which is a KAP 140. My instructor and I have yet to prove this to me, but he is stating that because the autopilot is NOT integrated into the G1000 system, it will not fly the LPV glide path. Is he correct?

Thanks to all.

Why isn't the autopilot integrated into the G1000? You all just use it for a wing leveler?

 

[James331]

No it's not technically a precision approach.

However in real life, it's basically a different flavor of ILS.


On the G1000 question, I'd imagine if it has a approach mode and can follow a ILS it would follow a LPV, but I really don't know for sure, try it in VFR/VMC, or check out the manual.

 

[JasonM]

Is your airplane WAAS?

 

[AlanM]

Thanks for the AIM reference / really clarified things.

The autopilot is a full autopilot but just not a Garmin. Per Garmin, the KAP140 will NOT track an LPV glide path. Oh well.

 

[MAKG1]

Why isn't the autopilot integrated into the G1000? You all just use it for a wing leveler?

The GFC700 will fly VNAV, but the KAP140 won't. It just captures and holds altitude. It will follow a true ILS glideslope, but not a GPS-manufactured one.

It's not that the autopilot isn't "integrated." It is, and will happily fly GNSS LNAV (provided that's what the CDI has selected). And KAP140s came stock with early G1000s. It's that it doesn't have VNAV.

 

[jordane93]

An LPV is technically not a pecision approach altohugh you have vertical and lateral guidence.

 

[Velocity173]

The GFC700 will fly VNAV, but the KAP140 won't. It just captures and holds altitude. It will follow a true ILS glideslope, but not a GPS-manufactured one.

It's not that the autopilot isn't "integrated." It is, and will happily fly GNSS LNAV (provided that's what the CDI has selected). And KAP140s came stock with early G1000s. It's that it doesn't have VNAV.

Ok, sounds like it's an older AP I guess. Our Cobham AP is interfaced with the 430/530 and will fly an LPV just fine.

 

[midlifeflyer]

It is technically a nonprecision approach because it's not one in ICAO language.

It is a precision approach in reality, even in the "real" world of the instrument PTS.

A localizer performance with vertical guidance (LPV) approach with a decision altitude (DA) greater than 300 feet height above terrain (HAT) may be used as a nonprecision approach; however, due to the precision of its glidepath and localizer-like lateral navigation characteristics, an LPV can be used to demonstrate precision approach proficiency (AOA VI TASK B ) if the DA is equal to or less than 300 feet HAT.​

 

[poadeleted20]

The GFC700 will fly VNAV, but the KAP140 won't. It just captures and holds altitude. It will follow a true ILS glideslope, but not a GPS-manufactured one.

The KAP 140 follows an LPV GS just fine (as well as LNAV/VNAV and LNAV+V, too), as that is generated off the GS needle to which it is coupled just as for an ILS GS. What it won't follow is VPATH/VNV vertical guidance.

From an operational standpoint, the only thing that's different due to LPV being technically a nonprecision approach compared to ILS as a precision approach is that you have to use 800-2 rather than 600-2 as the standard alternate minimum for any RNAV(GPS) approach even if LPV is available.

 

[RotorDude]

It is technically a nonprecision approach because it's not one in ICAO language.

It is a precision approach in reality, even in the "real" world of the instrument PTS.

A localizer performance with vertical guidance (LPV) approach with a decision altitude (DA) greater than 300 feet height above terrain (HAT) may be used as a nonprecision approach; however, due to the precision of its glidepath and localizer-like lateral navigation characteristics, an LPV can be used to demonstrate precision approach proficiency (AOA VI TASK B ) if the DA is equal to or less than 300 feet HAT.​

I think one important distinction where LPV is not considered "precision" approach by the FAA is for alternate airport requirement, where LPV requires 800/2 forecast conditions at the time of arrival, just like NDB, VOR and other non-precision approaches. Only ILS, PAR or GLS are considered "precision" for this purpose and allow 600/2 alternate planning minimums.

Standard alternate minimums for non-precision approaches and approaches with vertical guidance [NDB, VOR, LOC, TACAN, LDA, SDF, VOR/DME, ASR, RNAV (GPS) or RNAV (RNP)] are 800-2. Standard alternate minimums for precision approaches (ILS, PAR, or GLS) are 600-2.

 

[azure]

I seem to recall that another significant difference between LPV and ILS is in the requirements for lighting systems. Unless there is an ILS to the same runway, you may not find a precision runway lighting system (e.g., a "rabbit") even though LPV minimums exist. One example I can think of is the RNAV/GPS 24 @KIKW.

Not sure if LPV minimums require precision markings...

 

[RotorDude]

I seem to recall that another significant difference between LPV and ILS is in the requirements for lighting systems. Unless there is an ILS to the same runway, you may not find a precision runway lighting system (e.g., a "rabbit") even though LPV minimums exist. One example I can think of is the RNAV/GPS 24 @KIKW.

Not sure if LPV minimums require precision markings...

I am sure one of the experts can quote chapter and verse, but I think that you won't find LPV to 200' and 1/2 minimums without a functioning approach lighting system and other runway related requirements, just like the ILS. (KIKW LPV to 24 is 386' and 1-1/4.)

 

[azure]

I am sure one of the experts can quote chapter and verse, but I think that you won't find LPV to 200' and 1/2 minimums without a functioning approach lighting system and other runway related requirements, just like the ILS. (KIKW LPV to 24 is 386' and 1-1/4.)

Yes - good point and I wasn't trying to imply otherwise.

 

[JasonM]

It prob. wont fly the LPV approach because your G1000 is not WAAS enabled and the LPV in not a valid approach for your aircraft. I went though the same thing with my non-WAAS 182 I used to own.

 

[James331]

It prob. wont fly the LPV approach because your G1000 is not WAAS enabled and the LPV in not a valid approach for your aircraft. I went though the same thing with my non-WAAS 182 I used to own.

I'm surprised it even shows LPVs, all the non WAAS boxes I've flown won't show LPV, LP, etc approaches.

 

[azure]

I'm surprised it even shows LPVs, all the non WAAS boxes I've flown won't show LPV, LP, etc approaches.

The only difference between an LPV approach and a straight LNAV approach is in the existence of a GS and the annunciation "LPV" when flown with a WAAS GPS. A non-WAAS box (or a WAAS box without WAAS available) should still show the approach because it's an RNAV/GPS approach. Without WAAS you can still fly it to LNAV-only minimums.

 

[John Collins]

I am sure one of the experts can quote chapter and verse, but I think that you won't find LPV to 200' and 1/2 minimums without a functioning approach lighting system and other runway related requirements, just like the ILS. (KIKW LPV to 24 is 386' and 1-1/4.)

It is the same for ILS. Without the approach lights, the LPV 200 foot minimum carries the 1/4 SM visibility penalty. So at KUZA RWY 2 has MALSR, both the ILS and LPV are 200-1/2. If the MALSR is OOS, the minimums are 200-3/4. Over at KLKR RWY 6, there isn't an ALS, but the minimums are 200-3/4, same as if the ALS was installed, but OOS.

 

[John Collins]

It prob. wont fly the LPV approach because your G1000 is not WAAS enabled and the LPV in not a valid approach for your aircraft. I went though the same thing with my non-WAAS 182 I used to own.

Just a technical semantic point, there are no LPV approaches per say, there are RNAV (GPS) approaches which may have LPV minimums and or LNAV/VNAV minimums and or LNAV minimums or LP minimums. One is cleared for the RNAV approach and which minimums the pilot chooses is based on their equipment and the annunciation at the time of the approach. Not all WAAS GPS systems can fly RNAV approaches with LP minimums, for example most G1000 systems.

 

[aterpster]

The only difference between an LPV approach and a straight LNAV approach is in the existence of a GS and the annunciation "LPV" when flown with a WAAS GPS. A non-WAAS box (or a WAAS box without WAAS available) should still show the approach because it's an RNAV/GPS approach. Without WAAS you can still fly it to LNAV-only minimums.

That is not correct. The LPV lateral and vertical protected airspace is exactly the same as an ILS. That is quite different than LNAV or LNAV/VNAV.

Also, the LPV approach's final approach segment has alerting, accuracy, and integrity a whole lot better than LNAV or LNAV/VNAV.

 

[aterpster]

I am sure one of the experts can quote chapter and verse, but I think that you won't find LPV to 200' and 1/2 minimums without a functioning approach lighting system and other runway related requirements, just like the ILS. (KIKW LPV to 24 is 386' and 1-1/4.)

Yes. To have a DA of 200 feet, an LPV runway must have a parallel taxiway.

The siting criteria for ILS are much more strict. The FAA relaxed them to get LPV into Podunk airports provided the approach surfaces are clear.

For everyone: LPV is, in fact, a Category I precision approach. The issue is ICAO, not the FAA. The FAA is/was too nervous about upsetting the ICAO "apple cart." Perhaps this will change soon, now that Europe is going with LPV where they can (albeit more conservatively with airport standards, because they don't promote light airplane G/A over there.)

 

[azure]

That is not correct. The LPV lateral and vertical protected airspace is exactly the same as an ILS. That is quite different than LNAV or LNAV/VNAV.

Also, the LPV approach's final approach segment has alerting, accuracy, and integrity a whole lot better than LNAV or LNAV/VNAV.

I overstated my point then - I was only trying to answer the question about why a non-WAAS receiver should show the approach at all. It is still an RNAV/GPS approach was my point - essentially what John said much better than I.

Thanks for the correction!

 

[RotorDude]

Yes. To have a DA of 200 feet, an LPV runway must have a parallel taxiway.

The siting criteria for ILS are much more strict. The FAA relaxed them to get LPV into Podunk airports provided the approach surfaces are clear.

For everyone: LPV is, in fact, a Category I precision approach. The issue is ICAO, not the FAA. The FAA is/was too nervous about upsetting the ICAO "apple cart." Perhaps this will change soon, now that Europe is going with LPV where they can (albeit more conservatively with airport standards, because they don't promote light airplane G/A over there.)

OK, question with a guessed answer: if LPV is essentially a Cat I precision approach, why the penalty in choosing it as alternate (800/2 vs. 600/2)?
My guess is that it's due to the (not-unfounded) fear that the reason you need to divert to the alternate is that there is some kind of systemic GPS issue, either on board or outside, and the penalty reflects the possibility of perhaps losing the WAAS capability. What say the experts?

 

[azure]

So just to clarify then: if you don't have a WAAS receiver, or WAAS isn't available, obviously you won't have a GS, but what about the lateral sensitivity? I've always thought that the LOC-like lateral sensitivity depended on having WAAS as well, and would not be present without it. i.e. without WAAS, the approach looks like a straight LNAV approach (or LNAV/VNAV if you happen to have baro-VNAV). Correct or not?

 

[RotorDude]

So just to clarify then: if you don't have a WAAS receiver, or WAAS isn't available, obviously you won't have a GS, but what about the lateral sensitivity? I've always thought that the LOC-like lateral sensitivity depended on having WAAS as well, and would not be present without it. i.e. without WAAS, the approach looks like a straight LNAV approach (or LNAV/VNAV if you happen to have baro-VNAV). Correct or not?

I think when you revert from LPV to LNAV due to losing WAAS, you might need to use a different approach procedure altogether, since the missed approach or other parameters may be different (MAP, step downs?), so it's not just the minimums that may change, and it's not like ILS simply reverting to LOC on GS loss.

 

[aterpster]

OK, question with a guessed answer: if LPV is essentially a Cat I precision approach, why the penalty in choosing it as alternate (800/2 vs. 600/2)?
My guess is that it's due to the (not-unfounded) fear that the reason you need to divert to the alternate is that there is some kind of systemic GPS issue, either on board or outside, and the penalty reflects the possibility of perhaps losing the WAAS capability. What say the experts?

Yes, it is an issue of continuity. You don't know whether LPV is going to be available until you get the LPV annunciation.

 

[azure]

I think when you revert from LPV to LNAV due to losing WAAS, you might need to use a different approach procedure altogether, since the missed approach or other parameters may be different (MAP, step downs?), so it's not just the minimums that may change, and it's not like ILS simply reverting to LOC on GS loss.

Why? The approach plate doesn't say "LPV" in the title, it says RNAV(GPS). LPV approaches typically also have LNAV-only and/or LNAV/VNAV minimums. I don't know for sure that they don't exist, but I've never seen an LPV approach with a separate MA procedure for LPV minimums vs. for straight LNAV minimums. If you don't have WAAS, you observe the LNAV minimums, the minimum altitude becomes a MDA, and the MAP is at a waypoint in the database, usually (always?) RWxx, where xx is the runway number. If you have WAAS, and you fly the GS, then the minimum altitude is the DH and the MAP is when you reach it on the GS.

When my plane gets back from annual I'm going to have to try disabling WAAS on my 480 and then fly an RNAV(GPS) approach that has LPV minimums. What I'd expect to happen is that it would annunciate LNAV instead of LPV. And to me, that would indicate that I had LNAV lateral sensitivity instead of the more LOC-like precision when LPV is annunciated.

Edited to correct RNAV/GPS - RotoDude is correct, it is actually RNAV(GPS).

 

[RotorDude]

Why? The approach plate doesn't say "LPV" in the title, it says RNAV/GPS. LPV approaches typically also have LNAV-only and/or LNAV/VNAV minimums. I don't know for sure that they don't exist, but I've never seen an LPV approach with a separate MA procedure for LPV minimums vs. for straight LNAV minimums. If you don't have WAAS, you observe the LNAV minimums, the minimum altitude becomes a MDA, and the MAP is at a waypoint in the database, usually (always?) RWxx, where xx is the runway number. If you have WAAS, and you fly the GS, then the minimum altitude is the DH and the MAP is when you reach it on the GS.

When my plane gets back from annual I'm going to have to try disabling WAAS on my 480 and then fly an RNAV/GPS approach that has LPV minimums. What I'd expect to happen is that it would annunciate LNAV instead of LPV. And to me, that would indicate that I had LNAV lateral sensitivity instead of the more LOC-like precision when LPV is annunciated.

It doesn't say LPV, but it might say RNAV (GPS) Z, RNAV (GPS) Y, etc., where each could have different modes and different minimums. But I stand to be corrected.

 

[RotorDude]

Yes, it is an issue of continuity. You don't know whether LPV is going to be available until you get the LPV annunciation.

Thanks. So WAAS availability for LPV is considered less reliable than the GS for an ILS?
(Anecdotally I have personally experienced more GS failures than WAAS failures, but I guess that's not scientific.)

 

[azure]

It doesn't say LPV, but it might say RNAV (GPS) Z, RNAV (GPS) Y, etc., where each could have different modes and different minimums. But I stand to be corrected.

True. But are there any RNAV(GPS) approaches that have LPV minimums that do NOT have straight LNAV or LNAV/VNAV minimums? They might exist, I don't know for sure, but I've never encountered one.

 

[JasonM]

Just a technical semantic point, there are no LPV approaches per say, there are RNAV (GPS) approaches which may have LPV minimums and or LNAV/VNAV minimums and or LNAV minimums or LP minimums. One is cleared for the RNAV approach and which minimums the pilot chooses is based on their equipment and the annunciation at the time of the approach. Not all WAAS GPS systems can fly RNAV approaches with LP minimums, for example most G1000 systems.

I guess that can get confusing and I do understand that. My current airplane is WAAS and will show the LPV and GS if reception is good enough. If not it will revert to the standard RNAV. I guess what I was trying to say is that the GS (the LPV special sauce) wont work unless you are WAAS. At least that is how it was in my 2004 G1000 T182T I had. It would show RNAV(LNAV/VNAV) but never show an option for the LPV. I would get a GS on VNAV profiles of the approach occasionally, but never from the FAF in.

 

[RotorDude]

True. But are there any RNAV(GPS) approaches that have LPV minimums that do NOT have straight LNAV or LNAV/VNAV minimums? They might exist, I don't know for sure, but I've never encountered one.

I can't say I have run into this in real life, but I am pretty sure I have seen examples of separate plates for LPV vs. LNAV, and the caveat that if you lose WAAS/LPV, you shouldn't just automatically continue the same approach to LNAV minimums. For one thing, I think LNAV minimums are actually lower in some cases.

OK, found this document, where it says (emphasis mine):

It is possible to have LP and LNAV published on the same approach chart, but LP will only be published if it provides lower minima than the associated LNAV line of minima

and

LP is not a fail-down mode for LPV. The avionics integration may include advisory vertical guidance during an LP approach to an LP line of minima.

So if "it is possible" to have a common plate, it's also possible to have them separate (presumably where details like stepdowns or missed approach make it impossible to use the same page).

I realize that I may be conflating LP and LNAV, which are different (but related) animals, but my assumption is that the same issues are relevant to both LPV vs. LNAV and LPV vs. LP.
Of course I stand to be corrected on all these points.

 

[poadeleted20]

I am sure one of the experts can quote chapter and verse, but I think that you won't find LPV to 200' and 1/2 minimums without a functioning approach lighting system and other runway related requirements, just like the ILS. (KIKW LPV to 24 is 386' and 1-1/4.)

And conversely, I think you can find ILS's to runways without an approach lighting system, but the mins will be higher than 200-1/2 -- and you may find the same higher mins for an LPV to the same runway.

 

[poadeleted20]

It prob. wont fly the LPV approach because your G1000 is not WAAS enabled and the LPV in not a valid approach for your aircraft. I went though the same thing with my non-WAAS 182 I used to own.

If it shows LPV, it's WAASified, and the KAP 140 will fly the LPV glide slope just the same as it does for an ILS glide slope.

 

[poadeleted20]

The only difference between an LPV approach and a straight LNAV approach is in the existence of a GS and the annunciation "LPV" when flown with a WAAS GPS.

There are a lot of other differences, although they are mostly hidden inside the box. The one which is not is the increased lateral sensitivity.

A non-WAAS box (or a WAAS box without WAAS available) should still show the approach because it's an RNAV/GPS approach. Without WAAS you can still fly it to LNAV-only minimums.

And without WAAS, you'll never see the LPV annunciation, which should be a big clue not to fly to LPV mins.

 

[poadeleted20]

So just to clarify then: if you don't have a WAAS receiver, or WAAS isn't available, obviously you won't have a GS, but what about the lateral sensitivity?

In those cases, you'll have the standard LNAV sensitivity, and with a WAAS unit, you'll see the LNAV annunciation instead of LPV or LP.

I've always thought that the LOC-like lateral sensitivity depended on having WAAS as well, and would not be present without it.

That is correct.

i.e. without WAAS, the approach looks like a straight LNAV approach (or LNAV/VNAV if you happen to have baro-VNAV).

Correct.

 

[poadeleted20]

I think when you revert from LPV to LNAV due to losing WAAS, you might need to use a different approach procedure altogether, since the missed approach or other parameters may be different (MAP, step downs?), so it's not just the minimums that may change, and it's not like ILS simply reverting to LOC on GS loss.

That would be true if the RNAV(GPS) approach you're using has only LPV mins, but I've never seen one like that. What you may see, however, is two RNAV(GPS) approaches, one with an Y and one with a Z in the title. One will have LPV mins as well as LNAV mins, while the other will have only LNAV mins. See the RNAVY(GPS) Y and Z approaches to Runway 23 at FDK.
http://155.178.201.160/d-tpp/1506/05089RY23.PDF
http://155.178.201.160/d-tpp/1506/05089RZ23.PDF
If you lose WAAS on the Z approach, it still has LNAV mins, so you can continue to those LNAV mins. However, because of the issues you mentioned, the LNAV-only Y approach has lower mins than the LNAV mins on the Z approach, so with WAAS out, you'd want to fly the LNAV-only Y approach to have your best chance of breaking out.

 

[RotorDude]

That would be true if the RNAV(GPS) approach you're using has only LPV mins, but I've never seen one like that. What you may see, however, is two RNAV(GPS) approaches, one with an Y and one with a Z in the title. One will have LPV mins as well as LNAV mins, while the other will have only LNAV mins. See the RNAVY(GPS) Y and Z approaches to Runway 23 at FDK.
http://155.178.201.160/d-tpp/1506/05089RY23.PDF
http://155.178.201.160/d-tpp/1506/05089RZ23.PDF
If you lose WAAS on the Z approach, it still has LNAV mins, so you can continue to those LNAV mins. However, because of the issues you mentioned, the LNAV-only Y approach has lower mins than the LNAV mins on the Z approach, so with WAAS out, you'd want to fly the LNAV-only Y approach to have your best chance of breaking out.

Thank you for the example. My assumption is that in your example, flying the GPS Z LPV and losing WAAS, you can't just quietly revert to the GPS Y LNAV on your own (though you can revert to GPS Z LNAV), since reverting to a different approach such as GPS Y means you'll be flying a different missed approach.
I guess if you lose comms (or are nordo to start with) you could do that, but otherwise you'd need a new approach clearance (or a retroactive one, if there is such a thing) from ATC for the GPS Y.
This used to be so simple when you just lost GS and reverted to LOC all on your own.

 

[azure]

There are a lot of other differences, although they are mostly hidden inside the box. The one which is not is the increased lateral sensitivity.

Yep - I know. I was being sloppy, and Wally corrected me.

And without WAAS, you'll never see the LPV annunciation, which should be a big clue not to fly to LPV mins.

Yes, that's the giveaway that the approach has fallen back to LNAV.