IFR Alts AIM 1-2-3.d.1

Discussion in 'Cleared for the Approach' started by PilotRPI, Dec 26, 2018.

  1. PilotRPI

    PilotRPI Line Up and Wait

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    In this section, can someone clarify a, b, and c? I’m clear that non-waas can have a gps primary OR alternate, and am familiar with the 2-600 and 2-800 planning rules. What about a-c below? It says we “may” plan minimums on certain gps related approach types. Does that mean at the gps alternate, I can use the lnav mins instead of the 2-800 rule or something like that?

    67AC9250-687A-4691-ABC2-1B58CAD81578.jpeg
     
  2. asicer

    asicer En-Route

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    Not entirely sure what you're trying to ask in your question, but the 600/800 rule only applies to flight planning. Once you are actually at the alternate, those rules go away and you fly the procedure.
     
  3. PilotRPI

    PilotRPI Line Up and Wait

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    Thanks, aware of that. Im asking what a, b, and c mean in normal person speak. Do they affect the 2-600 rule for panning when using non-waas gps?

    After spending a bumch more time, including 1-1-17b.5.c, 1-1-18c.9.a, and 91.169. I’m wondering if a, b, and c just means you can use those approaches as the planned alternates, but you still need to use the 2-600/2-800 weather mins from 91.169.
     
    Last edited: Dec 26, 2018
  4. Palmpilot

    Palmpilot Touchdown! Greaser!

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    That's the way it looks to me. I don't think it changes the minimums in the regulations, because that would require an NPRM.
     
  5. midlifeflyer

    midlifeflyer Final Approach

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    I'm confused too. Let's see if this answers it.

    Assuming a on-WAAS GPS:

    1. Either your destination or your alternate may be exclusively GPS, but not both. So, for a simple example, if your destination only has RNAV approaches, you must have an ILS available at your alternate.
    2. You are still subject to 91.169. IOW, your alternate must be available as, and meet the criteria for an alternate. If you are planning an ILS at the alternate, that's your 600/2; if anything else, 800/2 (unless, of course, it's noted NA or as having special alternate minimums).

    (a), (b) and (c) are just one of those belt-and-suspender things saying it doesn't matter whether the GPS approach is LNAV, LNAV/VNAV, Baro-VNAV, etc. That there are no restrictions based on they type of GPS approach.

    Does that answer what you are asking?
     
    Last edited: Dec 27, 2018
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  6. chemgeek

    chemgeek Line Up and Wait

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    The regs are as usual clear as mud...I THINK it says if you are WAAS equipped, both your destination and alternate can have GPS-only approaches, and alternate mins must meet 91.169, i.e. 800-2 (cannot assume vertical guidance for WAAS GPS). For non WAAS, it looks to me that the regs allow you to substitute the circling MDA for the alternate minimums for a GPS approach. (Often those are higher than 800-2.) Only one of the destination or alternate can be served by GPS-only approaches. All the stuff about baro-nav can be ignored for most flib flyers. The FAA clarification documentation is anything but...
     
  7. MauleSkinner

    MauleSkinner Final Approach

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    What a and b are saying is that they're nonprecision approaches, therefore 800&2 is the required forecast.

    I'm not sure whether RNP .3 is considered precision or nonprecision, but if you've got the approval you'd know. ;)
     
  8. benyflyguy

    benyflyguy Cleared for Takeoff

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    Bit of a thread drift question, what if the non-precision minimums are greater than 800/2, can you still listed as an alternate?
     
  9. chemgeek

    chemgeek Line Up and Wait

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    Isn't 800-2 the default only if no alternate minimums are listed?
     
  10. aterpster

    aterpster Pattern Altitude

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    The only precision approaches are ILS, GLS, and PAR. LPV and LNAV/VNAV are approaches with vertical guidance (APV). RNP .3 is a performance-based navigation specification for lateral guidance.
     
    Last edited: Dec 27, 2018
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  11. midlifeflyer

    midlifeflyer Final Approach

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    Yes.
     
  12. midlifeflyer

    midlifeflyer Final Approach

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    That's what the inverse "A" on approach plates is for: to tell you there are different alternate minimums for that approach or it is not usable for alternate planning at all.
     
  13. MauleSkinner

    MauleSkinner Final Approach

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    I find it interesting that LPV is considered a precision approach for PTS/ACS purposes, but Nonprecision for pretty much everything else.
     
  14. aterpster

    aterpster Pattern Altitude

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    No, not non-precision. It's a APV with a decision altitude. It's an ICAO thing that prevents it from being a precision approach. LPV uses exactly the same TERPs as does CAT I ILS.
     
  15. MauleSkinner

    MauleSkinner Final Approach

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    It’s designed like an ILS, but as you say, “an ICAO thing” prevents it from being a precision approach, so operationally we have to treat it as a Nonprecision approach. APV has no legal status in operations for alternate minimums or anything else I can find.
     
  16. Palmpilot

    Palmpilot Touchdown! Greaser!

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    I couldn't figure out where to find the alternate minimums in ForeFlight, so I Googled it and found this:

    "The IFR Alternate Airport Minimums are similarly found in the Airports section of ForeFlight. When in the Procedures section of the Airports tab, select Arrival from the list of options at the left, and you’ll then see Alternate Minimums displayed at the top."

    https://ipadpilotnews.com/2017/02/chart-supplements-legends-foreflight/

    Putting it in the Arrival section seems non-intuitive to me, but now I know.
     
  17. aterpster

    aterpster Pattern Altitude

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    I agree, for alternate planning only. Another example of the FAA's left-hand/right-hand syndrome. o_O
     
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  18. chemgeek

    chemgeek Line Up and Wait

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    I THINK the FAA "logic" is that vertical guidance is not assured, so they ask us to plan for the worst case scenario. To be honest, I've never ever seen a vertical guidance integrity failure except when the vertical guidance board in my GNS430 failed. It took until 2013 for the FAA to trust GPS enough to allow us to use GPS only for destinations AND alternate planning. Ironic, since GPS is the ONLY available approach for many airports, and LPVs are a godsend for non-metro airports
     
  19. MauleSkinner

    MauleSkinner Final Approach

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    Although, as I think about it...my recollection is that 135 (and I assume 121) OpSpecs use approach minimums rather than PA/NPA designator to determine alternate airport forecast requirements, so a 200 & 1/2 LPV and an ILS to separate runways could get you down to a 400 & 1 forecast at the alternate.
     
  20. aterpster

    aterpster Pattern Altitude

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    Before we had WAAS navigators, the RAIM check provided fairly good assurance there would be availability at the destination and perhaps alternate. With WAAS the odds are overwhelming that LPV will be available at the alternate unless GPS is not at all available (jamming, or such). Part of the problem is the FAA doesn't like writing rules when they don't see the benefit.
     
  21. midlifeflyer

    midlifeflyer Final Approach

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    I don't care about FF's choices (except the one which makes us look for it after it pulls up the volume instead of going to the page). But now you have me curious. Given that its all about destination planning, where would you put it?
     
  22. aterpster

    aterpster Pattern Altitude

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    ForeFlight with Jepps makes all those data more accessible.
     
  23. Palmpilot

    Palmpilot Touchdown! Greaser!

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    The first thing I do when I'm planning an alternate is to look at the approaches that are available for that airport. Since I'm in the Approach section when I see the "A" for non-standard alternate minimums, to me that's the section that would be a more obvious place in which to look for what those non-standard minimums are. I would have expected to see only arrival procedures in the arrival section.
     
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  24. John Collins

    John Collins Pattern Altitude

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    The basic logic of alternate planning assumes that the approach may be flown under worst case conditions. So the 600-2 for a precision approach, the worst case conditions would assume the GS was out of service and that the localizer option would be used and that circling might be required. The 600-2 usually will meet the worst case conditions for a localizer. When it doesn't, higher alternate minimums are specified. In the case of a non WAAS GPS dependent on RAIM availability and adequate geometry of the satellites, it is only prudent that you only use GPS for your destination or your alternate, but not both. With WAAS, basic RNAV (GPS) LNAV integrity is now considered almost a sure thing and a WAAS GPS does not have the limitation requiring supplementary navigation and can be used as the sole source for satisfying 91.205 for IFR navigation.

    So with a typical RNAV (GPS) approach, with a WAAS GPS, the worst case conditions are that the vertical guidance is not available or that the lateral precision may not be met for LP and you have to fly the approach using the LNAV minimums and have to circle to land. When those exceed 800-2, you will see the inverted A indicating special alternate minimums.

    There are other criteria that must be met in order for an approach to be usable as an alternate, the approach lateral guidance must be monitored or the procedure will have the reverse "A" NA indicated. Also, there must be a local altimeter setting available, so you will often see the note NA when local weather not available or when the tower is closed. At my airport, Rock Hill, SC, KUZA, there is an ILS or LOC RWY 2 approach, but since the airport is not towered, the ILS is not monitored, so it can't be used as an alternate. The RNAV (GPS) RWY 2 can be used as an alternate, because WAAS is monitored at the national level. The alternate minimums are 800-2 except for Cat D, where they are set to 800 - 2 1/4 because the circle to land on this procedure requires 674 and 2 1/4 NM for category D. this approach also has the note "NA when local weather not available".

    Look at the Alternate minimums for KJQF, Concord, NC and you should be able to figure out why the alternate minimums for the ILS 20 for category D are upped from 600-2 to 800-2 1/2.