Plan to use LNAV or Circling minimums for RNAV approach at alternate

Discussion in 'Cleared for the Approach' started by Mike Gagnon, Jan 5, 2022.

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1. Mike GagnonPre-Flight

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I'm struggling to understand the significance of text in AIM 1-1-18c.9.(a), where it says "When using WAAS at an alternate airport, flight planning must be based on flying RNAV (GPS) LNAV or circling minima line...".

We're already going to be using non-precision alternate minimums (800-2) for the RNAV approach - what are the implications of having to plan to use the LNAV or circling minimums? How might that impact planning?

Note that I understand that if LPV is available, you can fly that when you get there - that's not a question. I'm just trying to understand how this need to use the LNAV minimums for planning purposes changes things.

2. MauleSkinnerTouchdown! Greaser!

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If the LNAV
or circling MDA/vis is greater than 800&2, you’ll need to adjust the weather minimums for your alternate.

3. chemgeekEn-Route

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This clause probably accounts for LNAV approaches with minima above 800/2, of which are are many, including at my home field.

4. RussREn-Route

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True, but that will already be published as non-standard alternate minimums for the procedure. So those would be the alternate minimums regardless of which line of minimums he plans to fly.

Like the OP, I am also not sure how to apply the AIM paragraph.

5. Mike GagnonPre-Flight

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Yes, I should have stated that I have the same assumption here that non-standard minimums would exist and be used in this case.

6. MauleSkinnerTouchdown! Greaser!

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The AIM is explaining why the alternate minimums line exists.

if the AIM statement wasn’t there, the question would probably be why the alternate minimums increase when the approach goes as low as 200 & 1/2.

7. midlifeflyerTouchdown! Greaser!

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I have a feeling you are correct. It's an explanation, not an admonition. But even so, the sentence structure is pretty abysmal.

8. MauleSkinnerTouchdown! Greaser!

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An official FAA document with abysmal sentence structure?!?

9. N1120APattern Altitude

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More importantly, at what point will they allow 600/2 for LPV?

10. MauleSkinnerTouchdown! Greaser!

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They’d either have to redefine LPV as a precision approach or change the reg to specifically include LPV for the 600 & 2 alternate minimums. This “problem” isn’t something new or unknown to the FAA, and I haven’t heard any official noises that they’re looking at it, I don’t expect any action on it.

Last edited: Jan 5, 2022
11. N1120APattern Altitude

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You'd think they'd do it with MON

12. MauleSkinnerTouchdown! Greaser!

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MON?

13. WDDEn-Route

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Either 1) Tuesday would be a better day to do that, or 2) Minimum Operational Network - which I thought was describing reducing VOR towers to a lower number as a GPS back up. Not sure how that factors into re defining LPV as a precision approach to allow it to be used for 600 fee 2mile alternative requirement.

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14. N1120APattern Altitude

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Minimum Operational Network. Some ILS will eventually be scrapped and LPV will be the best alternative.

15. MauleSkinnerTouchdown! Greaser!

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I’d be willing to bet that was figured into what defines “minimum”. At least in the FAA’s view.

16. midlifeflyerTouchdown! Greaser!

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I think we'll see it within the next 5 years. OTOH, I think it will be a while before we see many ILS approaches go away. When you think how far we've come in such a short time with GPS acceptance, it's really not that big a step.

17. WDDEn-Route

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Is there an airport today that doesn’t have an LPV?

18. midlifeflyerTouchdown! Greaser!

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"Minimum" refers to the minimum number of enroute VORs (with an expanded service ceiling) needed to allow one to navigate to an airport with an ILS, LOC or VOR approach in case of a GPS system failure.

if you are seeing VORs decommissioned and associated Victor airways being terminated in your area, that's MON.

The widespread removal of VOR approaches is somewhat related since you obviously can't have a VOR approach without a VOR, but is actually part of a separate program. You can see that in my area. We have a nearby VOR which is being retained as part of MON but VOR approaches to at least two airports which used it have been terminated.

19. midlifeflyerTouchdown! Greaser!

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There are plenty of airports with GPS approaches without LPV minimums. DZJ about 60nm NE of you has only one GPS approach and it's LNAV only.

Last edited: Jan 6, 2022
20. RussREn-Route

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Thousands. Click around to some local airports, you'll find them easily.

Having LPV minimums requires a certain amount of cleared area off the approach end of the runway, called the Vertical Guidance Surface. The most common obstacle penetrating this surface? Trees.

21. midlifeflyerTouchdown! Greaser!

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After checking his location i found the one I mentioned in about a minute.

22. WDDEn-Route

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23. midlifeflyerTouchdown! Greaser!

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I'm on a diet. No cookies. I prefer large bills.

24. MauleSkinnerTouchdown! Greaser!

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You’re more of a Platypus man, huh?

25. midlifeflyerTouchdown! Greaser!

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As soon as I hit "Post Reply," I just knew...

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