LPV as alternate. 600 or 800 feet?

[jssmith.lh]

During my IPC today the topic of ceilings and visibility at alternate came up. Precision approach at alternate ceilings must be 600. Non-precision ceilings must be 800.
Given that for a checkride an LPV is counted as a precision approach, how is it counted when selecting an alternate?

 

[Clip4]

AIM 1-2-3
d. Alternate Airport Considerations. For the purposes of flight planning, any required alternate airport must have an available instrument approach procedure that does not require the use of GPS. This restriction includes conducting a conventional approach at the alternate airport using a substitute means of navigation that is based upon the use of GPS. For example, these restrictions would apply when planning to use GPS equipment as a substitute means of navigation for an out−of−service VOR that supports an ILS missed approach procedure at an alternate airport. In this case, some other approach not reliant upon the use of GPS must be available. This restriction does not apply to RNAV systems using TSO−C145/−C146 WAAS equipment. For further WAAS guidance, see paragraph 1−1−18.
1. For flight planning purposes, TSO-C129() and TSO-C196() equipped users (GPS users) whose navigation systems have fault detection and exclusion (FDE) capability, who perform a preflight RAIM prediction at the airport where the RNAV (GPS) approach will be flown, and have proper knowledge and any required training and/or approval to conduct a GPS-based IAP, may file based on a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the
alternate airport, pilots may plan for applicable alternate airport weather minimums using:
(a) Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
(b) LNAV/vertical navigation (LNAV/ VNAV) DA, if equipped with and using approved barometric vertical navigation (baro-VNAV) equip- ment;
(c) RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baro-VNAV equipment and the pilot has verified required navigation performance (RNP) availability through an approved prediction program.
2. If the above conditions cannot be met, any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly.
3. This restriction does not apply to TSO-C145() and TSO-C146() equipped users (WAAS users). For further WAAS guidance, see paragraph 1−1−18.

 

[tsts4]

I vote 800-2. The AIM states for a WAAS box, that alternate flight planning must be made using only LNAV or circling minima. That leads me to believe that non-precision ceilings and vis apply. Note this is for planning only, if you actually fly to the alternate you can use the lowest minima the GPS annunciates.

 

[MauleSkinner]

RNAV to LPV minimums is not a precision approach. The ACSs allow them to be substituted for a precision approach if they meet certain criteria, but even the ACSs don’t say they ARE precision approaches.

 

[midlifeflyer]

During my IPC today the topic of ceilings and visibility at alternate came up. Precision approach at alternate ceilings must be 600. Non-precision ceilings must be 800.
Given that for a checkride an LPV is counted as a precision approach, how is it counted when selecting an alternate?

It's a "precision approach" for the checkride because the checkride is a skills test and there is basically no difference in the types of skills it takes to fly either.

What is a "precision approach" in a regulatory sense is tied up with its FAR definition, "a standard instrument approach procedure in which an electronic glide slope is provided, such as ILS and PAR." That, in turn, is part of how the international community certified things.

So, for alternate minimums, we're using the regulatory definition.

 

[WDD]

Yep - LPV is non precision in the book, and thus 800 feet apply. Does it make sense? Not really. It's just costly to certify them as Precision per international standards. Even though they are just as good as ILS.

And as more and more ILS are decommissioned, more and more "Precision" approaches will be lost. I know that it must be by international standards certified to become "Precision", but I don't know what the international rules are for minimums for "non precision". If not regulated, I could see the FAA at some point just make the rule change that a non precision approach that is an LPV needs to be at 610 foot minimums, and call it a day.

 

[tonycondon]

800

 

[midlifeflyer]

Yep - LPV is non precision in the book, and thus 800 feet apply. Does it make sense? Not really. It's just costly to certify them as Precision per international standards. Even though they are just as good as ILS.

I have not been keeping up with it but there is current activity about changing that, including a draft AC 90-119.

 

[midlifeflyer]

FWIW, especially with so many ILS approaches unmonitored (NA as an alternate), my current solution is to select a airport with an available ILS to check the box for a required alternate, but plan to go somewhere else.

 

[Clip4]

FWIW, especially with so many ILS approaches unmonitored (NA as an alternate), my current solution is to select a airport with an available ILS to check the box for a required alternate, but plan to go somewhere else.

The ICAO flight plan has fields for 2 alternate airports. You can list both.

 

[Martin Pauly]

Rumor has it the new AC 90-119 (currently in draft state, out for comments) will officially designate RNAV LPV approaches to be precision approaches, at least as far as the FAA goes.
I don't know if ICAO has anything similar on the horizon.

- Martin

 

[John Collins]

Yep - LPV is non precision in the book, and thus 800 feet apply. Does it make sense? Not really. It's just costly to certify them as Precision per international standards. Even though they are just as good as ILS.

And as more and more ILS are decommissioned, more and more "Precision" approaches will be lost. I know that it must be by international standards certified to become "Precision", but I don't know what the international rules are for minimums for "non precision". If not regulated, I could see the FAA at some point just make the rule change that a non precision approach that is an LPV needs to be at 610 foot minimums, and call it a day.

There is some logic to this. With an ILS, if the GS fails, you normally still have the localizer, so the lateral guidance is not degraded. If the ILS has a localizer only MDH above 600 feet, the 600 foot standard will be raised to accommodate the higher MDH. If the ILS does not have a localizer option, that procedure will be NA as an alternate. With LPV, if you lose the LPV annunciation, the downgrade is to LNAV and there isn't a downgrade equivalent to the localizer only option of the ILS. If the LPV does not have a LNAV option on the procedure, similar to the ILS without a Localizer option, the procedure will be NA for use as an alternate.

 

[midlifeflyer]

The ICAO flight plan has fields for 2 alternate airports. You can list both.

Three actually, takeoff, enroute, and destination. The others are not required for a domestic flight and I can't think of a good reason to add them.

 

[midwestpa24]

I've honestly thought the 600/800 rules are silly in general. Personally, if my destination is IFR, I want an alternate, preferable a VFR one. Always have an out.

 

[tsts4]

I've honestly thought the 600/800 rules are silly in general. Personally, if my destination is IFR, I want an alternate, preferable a VFR one. Always have an out.

It’s purely a fuel planning exercise. In reality you fly to wherever makes sense at the time, which may or may not be what you filed. While having VMC conditions within divert range of the destination would be preferable, many times it’s just not possible.

 

[MauleSkinner]

I've honestly thought the 600/800 rules are silly in general. Personally, if my destination is IFR, I want an alternate, preferable a VFR one. Always have an out.

I always preferred the 400 & 1 that I could use under Part 135.

 

[Clip4]

Three actually, takeoff, enroute, and destination. The others are not required for a domestic flight and I can't think of a good reason to add them.

The fields are provided to allow 121 carriers to meet the requirements of 121.619 and their airport authorizations.

 

[midlifeflyer]

The fields are provided to allow 121 carriers to meet the requirements of 121.619 and their airport authorizations.

I was kind of staying the the GA world.

 

[N1120A]

It is very silly to have an ILS and an LPV with the same minimums and the LPV requiring higher alternate minimums.

Rumor has it the new AC 90-119 (currently in draft state, out for comments) will officially designate RNAV LPV approaches to be precision approaches, at least as far as the FAA goes.
I don't know if ICAO has anything similar on the horizon.

- Martin

This would be excellent news. I guess the growing activation of LPV approaches outside the US and Canada is helping this.

I've honestly thought the 600/800 rules are silly in general. Personally, if my destination is IFR, I want an alternate, preferable a VFR one. Always have an out.

I file an alternate even with VMC predicted. It doesn't cost anything, so why not?

 

[RussR]

I file an alternate even with VMC predicted. It doesn't cost anything, so why not?

It's not always possible, though. Alternate airport selection is a function of fuel, as you have to have enough fuel to fly to your destination, then to your alternate, then for 45 more minutes.

If you have a maximum of 4 hours of fuel given your current payload, and your destination is 3 hrs 15 min away and VMC, you are legal to file IFR. But if you choose to file an alternate you will then need to offload some passengers (or cargo) to carry more fuel.

Yes, I've had this type of situation in Part 91 ops, and I'm sure it's a routine consideration in 121 and 135.

 

[N1120A]

It's not always possible, though. Alternate airport selection is a function of fuel, as you have to have enough fuel to fly to your destination, then to your alternate, then for 45 more minutes.

If you have a maximum of 4 hours of fuel given your current payload, and your destination is 3 hrs 15 min away and VMC, you are legal to file IFR. But if you choose to file an alternate you will then need to offload some passengers (or cargo) to carry more fuel.

Yes, I've had this type of situation in Part 91 ops, and I'm sure it's a routine consideration in 121 and 135.

I understand this situation. I've even had this situation and, of course, assured my destination didn't require an alternate. That said, most of my flights are not in this sort of situation and I also prefer to make a fuel stop if I will not land with 60 minutes of fuel.

 

[texasclouds]

Eight hundo brah!

 

[WDD]

Trivia for your upcoming check ride. If you’re non WASS, either your primary or alternate can be a GPS approach, but not both.

 

[MauleSkinner]

Trivia for your upcoming check ride. If you’re non WASS, either your primary or alternate can be a GPS approach, but not both.

Same for non WAAS?

 

[WDD]

Same for non WAAS?

No - completely different……..

 

[flyingron]

The fact that LPV is non-precision seems to be more ICAO lipservice insanity than any real operational issue. I wish the FAA would either get with the ICAO program or tell the to fudge off and stop this half-assed compliance for being silly strategy. Excuse me while I get into position and hold.

 

[MauleSkinner]

The fact that LPV is non-precision seems to be more ICAO lipservice insanity than any real operational issue.

nobody’s claiming it’s operational. It’s a definition issue.

 

[WDD]

Yep - that definitional issue is getting in the way of it being used as a precision alternative.

To stir the pot even more, I think ILS will become like VOR MON in the future, with only a select few remaining.

 

[John Collins]

Trivia for your upcoming check ride. If you’re non WASS, either your primary or alternate can be a GPS approach, but not both.

Don't forget you can't plan to use an airport as an alternate based on a conventional procedure that has a dependency on DME or NDB if you are not equipped and would need to use GPS substitution. IOW with conventional GPS, you can depend on the GPS for either the destination or the alternate, but not both.

 

[John Collins]

The fact that LPV is non-precision seems to be more ICAO lipservice insanity than any real operational issue. I wish the FAA would either get with the ICAO program or tell the to fudge off and stop this half-assed compliance for being silly strategy. Excuse me while I get into position and hold.

It should happen soon. Once AC 90-119 is released, LPV will be classed as precision. Here is how the draft reads:

12.3.1.2 PA Operations. These 3D operations use either ground-based, GPS-derived, and/or integrated electronic vertical guidance from the RNP system to enable lateral and vertical navigation to decision altitude (DA)/decision heights (DH) at or below 250 feet above ground level (AGL) (depending on the presence of obstacles). Typically, these are shown as LPV or LNAV/VNAV (and ILS/GLS) DA/DHs.

Note 1: “Integrated electronic” vertical guidance used in this context includes barometric vertical navigation (baro-VNAV) and Satellite-based Augmentation System (SBAS)-based RNP system-calculated glidepath guidance.

Note 2: Some approach procedures that contain both precision and nonprecision features are internationally designated as “Approaches with Vertical Guidance (APV).” These 3D approach procedures use GPS or SBAS to generate integrated electronic vertical and lateral guidance from the RNP system. These procedures typically have LNAV/VNAV lines of minima to DA/DH as low as 251 feet AGL. In the United States, all procedures to a LPV DA (regardless of height above touchdown (HAT)) are considered 3D precision operations.

It is not clear yet whether or not LPV or LNAV/VNAV with DH 250 feet or lower and classed as precision approaches will enjoy the 600-2 weather requirements and may still require 800-2. I am not sure of the reason for this, but it may be that because ILS uses the localizer as its fail down if vertical guidance is not available which provides a precision lateral path whereas with LPV or LNAV/VNAV, they fail down to LNAV lateral path. ILS that has a DA/MDA or visibility without approach lights that is above 600-2 will publish a non standard alternate won't use the 600-2 standard minimums and will have have higher alternate minimums specified, example see KAVL ILS or LOC Rwy 35 alternate minimums. Also, many ILS at non towered airports are not monitored and can't be used as an alternate, whereas the RNAV LPV can be, example KUZA.

 

[WDD]

Good point - 60O 2 precision alternative ILS must be monitored.

FWIW - our local towered D a while ago had a NOTAM that it’s ILS was “not monitored” for some reason. Hence, not available as a precision alternative.

 

[robin ardoin]

Same for non WAAS?

Waas you tryin' to say??

 

[DesertNomad]

Yep - that definitional issue is getting in the way of it being used as a precision alternative.

To stir the pot even more, I think ILS will become like VOR MON in the future, with only a select few remaining.

Then hopefully they will change 61.65(d)(2)(ii)(C) so as to not effectively require VOR, ILS and GPS approaches.

 

[Martin Pauly]

It is not clear yet whether or not LPV or LNAV/VNAV with DH 250 feet or lower and classed as precision approaches will enjoy the 600-2 weather requirements and may still require 800-2. I am not sure of the reason for this, but it may be that because ILS uses the localizer as its fail down if vertical guidance is not available which provides a precision lateral path whereas with LPV or LNAV/VNAV, they fail down to LNAV lateral path.

Thanks for the update on AC 90-119, John.

I sure hope LPV approaches will eventually qualify for 600-2 alternate minimums. SBAS outages seem exceedingly rare - in all my flying, I have never experienced a fallback from LPV (or LP) to LNAV. Though I have experienced (very rarely) a full GPS outage, just like I have experienced localizer outages.

Regards,
Martin

 

[Pinecone]

I have had it happen one time, fallback from LPV to LNAV. RNAV 31 into KLNS.

 

[John Collins]

Thanks for the update on AC 90-119, John.

I sure hope LPV approaches will eventually qualify for 600-2 alternate minimums. SBAS outages seem exceedingly rare - in all my flying, I have never experienced a fallback from LPV (or LP) to LNAV. Though I have experienced (very rarely) a full GPS outage, just like I have experienced localizer outages.

Regards,
Martin

I would characterize LPV 200 outages as infrequent, but not rare. Some parts of the US seem to experience regular outages, for example near El Paso and southern New Mexico. Yesterday there was a CME impact that caused a lot of outages, mostly in Canada and Alaska.


Back on 4/23 of this year there was a big time outage, again due to a CME.



An issue with an LPV outage is that it is likely to mess up other nearby airports, whereas an ILS outage is more likely to only affect one airport. With the above outage of LPV 200, LNAV was rock solid and could be depended on as a fall back capability.





This site https://www.nstb.tc.faa.gov/AirportOutages/ will allow one to select various approaches and determine the number of outages. This is from Q2 2023. Green is 0 to 1, Yellow is 2-3, Orange is 4-10, Gray is 11-30, Red is 31+. El Paso was red at 60 outages for a total of 17,370 outage seconds over the quarter (about 7.8 million seconds), so still high availability, but the average outage for the 60 at KELP was approximately 5 minutes each.

 

[Martin Pauly]

I would characterize LPV 200 outages as infrequent, but not rare. Some parts of the US seem to experience regular outages, for example near El Paso and southern New Mexico. Yesterday there was a CME impact that caused a lot of outages, mostly in Canada and Alaska.

You make some good points, John. Thanks also for the links to the WAAS/LPV status and performance charts.

Still, if we can accept 800-2 as standard alternate minimums for true non-precision approaches, it seems strange that we are not considering any relaxation for having LPV capability. Outlier airports with more frequent SBAS/LPV outages could declare non-standard alternate minimums, of course. But given how vast an improvement LPV is over LNAV, I think some credit it justified.

Regards,
Martin

 

[N1120A]

The fact that LPV is non-precision seems to be more ICAO lipservice insanity than any real operational issue. I wish the FAA would either get with the ICAO program or tell the to fudge off and stop this half-assed compliance for being silly strategy. Excuse me while I get into position and hold.

So long as no one position and holds on your lawn! Lol.

LUAW is actually better phraseology for clarity and also various accents.

Yep - that definitional issue is getting in the way of it being used as a precision alternative.

To stir the pot even more, I think ILS will become like VOR MON in the future, with only a select few remaining.

That actually is true - there are ILS installations that will go away with MON..

It should happen soon. Once AC 90-119 is released, LPV will be classed as precision. Here is how the draft reads:



It is not clear yet whether or not LPV or LNAV/VNAV with DH 250 feet or lower and classed as precision approaches will enjoy the 600-2 weather requirements and may still require 800-2. I am not sure of the reason for this, but it may be that because ILS uses the localizer as its fail down if vertical guidance is not available which provides a precision lateral path whereas with LPV or LNAV/VNAV, they fail down to LNAV lateral path. ILS that has a DA/MDA or visibility without approach lights that is above 600-2 will publish a non standard alternate won't use the 600-2 standard minimums and will have have higher alternate minimums specified, example see KAVL ILS or LOC Rwy 35 alternate minimums. Also, many ILS at non towered airports are not monitored and can't be used as an alternate, whereas the RNAV LPV can be, example KUZA.

I don't really see a difference between LNAV and LOC anyway.

 

[midlifeflyer]

I don't really see a difference between LNAV and LOC anyway.

LOC (and LP) are angular, so they get tighter as you get closer to the runway, permitting lower minimums when there are obstacles to the sides of the approach path. Lateral LNAV deviation is constant.

 

[RussR]

I don't really see a difference between LNAV and LOC anyway.

LOC (and LP) are angular, so they get tighter as you get closer to the runway, permitting lower minimums when there are obstacles to the sides of the approach path. Lateral LNAV deviation is constant.

Correct. If you find an airport with an ILS, look at the LOC minimums. Then compare them with the LNAV minimums on the RNAV approach. Chances are pretty good the LOC minimums will be lower, because of the smaller obstacle evaluation area. May be only 20 or 40 feet, or it might be significantly more, but there's a difference.