Confusing language help

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Dave S.

Pre-takeoff checklist
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thetexan
Talking about using GPS approaches at alternates….

AIM 1-1-17 b5c states in part…

"... At the alternate airport, pilots may plan for:
  1. Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
  2. LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approved barometric vertical navigation (baro-VNAV) equipment;
  3. 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.
All approaches known to man and even those not yet conceived can fall into one of two standard alternate minimums(at least as of this writing)...(1)precision approaches with 600-2 or (2) non-precision approaches with 800-2.
All RNAV approaches including LPV fall into the latter of 800-2. Of course, any approach, including ground based approaches may have different non-standard minimums.

I am confused about the phrase "may plan for" and the purpose of that phrase.

What does it mean to "plan for" "Lateral navigation (LNAV) or circling minimum descent altitude (MDA)"? Let's look at it closely. It's telling me I can plan for LNAV or circling minimum MDAs. So what? I am going to plan on 800-2 if I will be doing an LNAV. What does the LNAV or circling MDA have to do with my planning of the approach. It doesn't have any bearing on the 800-2. Let's say that the weather is exactly 800-2 with no non-standard minimums. I can "plan" on doing the approach even if the LNAV MDA is at 900 or the circling MDA is at 1000. Maybe I'll be able to land, or maybe not.

Now I understand the good judgement involved here. But I don't understand why the AIM is telling me what I can plan for; or what "may plan for" means.

Since 1, 2, and 3 must be met in order for the airport to not have to have an approved instrument approach procedure other than GPS-based I can understand that. But what is it saying. Is it saying that the forecasted weather must, of course, be 800-2, AND, AND, it must also be at least as high as the LNAV MDA and circling MDA in order to meet the paragraph (d) test, (as well as 2 and 3)?

Someone please chime in.

tex
 
Selection and filing an alternate airport is a flight planning exercise. If you actually go there (you never have to) you can use any approach and fly to the minimums for that approach.
 
Here's my take on it: Introduction to GPS (avclicks.com) , see slides #57 through #73 (or cut to the chase and go directly to the bottom of #73). It has to do with "substitute" vs. "alternate" means of navigation as it applies to GPS vs. WAAS RNAV equipment. Take it slow.
 
I may be wrong but I thought an available GPS approach with LPV minimums meant 600-2 applied.
 
RingLaserGyroSandwich said:
I may be wrong but I thought an available GPS approach with LPV minimums meant 600-2 applied.
Click to expand...
LPV is not a precision approach.
From AIM 1-1-18:
b. Instrument Approach Capabilities
1. A class of approach procedures which provide vertical guidance, but which do not meet the ICAO Annex 10 requirements for precision ap- proaches has been developed to support satellite navigation use for aviation applications worldwide. These procedures are not precision and are referred to as Approach with Vertical Guidance (APV), are defined in ICAO Annex 6, and include approaches such as the LNAV/VNAV and localizer performance with vertical guidance (LPV). These approaches provide vertical guidance, but do not meet the more stringent standards of a precision approach.
 
Last edited:
MauleSkinner said:
LPV is not a precision approach.
From AIM 1-1-18:
b. Instrument Approach Capabilities
1. A class of approach procedures which provide vertical guidance, but which do not meet the ICAO Annex 10 requirements for precision ap- proaches has been developed to support satellite navigation use for aviation applications worldwide. These procedures are not precision and are referred to as Approach with Vertical Guidance (APV), are defined in ICAO Annex 6, and include approaches such as the LNAV/VNAV and localizer performance with vertical guidance (LPV). These approaches provide vertical guidance, but do not meet the more stringent standards of a precision approach.
Click to expand...
Combined with 14 CFR 91.169(c)(1)(i)(A) (now that I'm home and not on my phone) this seems to settle it.

Practically speaking, are there any reasons why the requirements for LPV minimum approaches should be stricter than for ILS approaches when the approach minimums are the same? I'm not clear on what the more "stringent standards" are that are relevant here.

Edit: the allowance during instrument checkrides to demonstrate a precision approach by doing a non-precision approach may be confusing some folks...

"due to the precision of its glidepath and localizer-like lateral navigation characteristics, an LPV minimums approach can be used to demonstrate precision approach proficiency if the DA is equal to or less than 300 feet HAT."
 
RingLaserGyroSandwich said:
Practically speaking, are there any reasons why the requirements for LPV minimum approaches should be stricter than for ILS approaches when the approach minimums are the same? I'm not clear on what the more "stringent standards" are that are relevant here.
Click to expand...
You’re reading it backwards…Precision approaches fall under a stringent standard that LPV doesn’t meet.

I don’t know what those standards are, specifically, but apparently they exist even though they appear “the same” to us.
 
MauleSkinner said:
You’re reading it backwards…Precision approaches fall under a stringent standard that LPV doesn’t meet.

I don’t know what those standards are, specifically, but apparently they exist even though they appear “the same” to us.
Click to expand...
Sorry I was unclear, I meant that 800-2 is stricter than 600-2 (from the pilot's perspective), not that the rules/standards for establishing approaches with LPV minimums are more strict.
 
RingLaserGyroSandwich said:
Practically speaking, are there any reasons why the requirements for LPV minimum approaches should be stricter than for ILS approaches when the approach minimums are the same?
Click to expand...
Not really. I never dove into it that completely but I think it's something about the electronic glideslope of the ILS vs the calculated glidepath of the LPV. But practically speaking it's only relevant to selection of a planning alternate. Regulation just hasn't caught up yet.
 
MauleSkinner said:
You’re reading it backwards…Precision approaches fall under a stringent standard that LPV doesn’t meet.

I don’t know what those standards are, specifically, but apparently they exist even though they appear “the same” to us.
Click to expand...
There is no difference between LPV and CAT I ILS. It is a concession to ICAO.

LPV alternate planning minimums are 800-2 because WAAS cannot be monitored by ATC, unlike many (most) ILS.
 
midlifeflyer said:
It shouldn't be. The ACS language seems pretty straightforward.
Click to expand...
I agree, but it's much easier for instrument pilots to remember that they did a GPS approach to LPV minimums to demonstrate a precision approach than it is to remember the exact wording in the ACS that probably not every candidate even read to begin with.
 
RingLaserGyroSandwich said:
I agree, but it's much easier for instrument pilots to remember that they did a GPS approach to LPV minimums to demonstrate a precision approach than it is to remember the exact wording in the ACS that probably not every candidate even read to begin with.
Click to expand...
Not reading the ACS is a "you" problem.
 
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