IFR Alternate

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Caterpillar
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IFR Alternate

Post by Caterpillar »

Good day everyone,

We’ve been debating within a few pilots on the following:

An airport with a non-precision approach, minimums are 900 (500), 1 1/4

What would be your IFR minimums, for both vis and ceiling? Also, can you use the sliding chart?

Thanks!
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Caterpillar
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Re: IFR Alternate

Post by Caterpillar »

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indieadventurer
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Re: IFR Alternate

Post by indieadventurer »

Non-precision approach, so 800-2 or 300-1 applies. This approach would require at least 800 2 1/4 and the sliding scale wouldn't apply as it doesn't meet standard alternate minima, 800-2, in this case.

Or am I missing something...

Edit for typo
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Last edited by indieadventurer on Sat Nov 09, 2019 4:08 pm, edited 1 time in total.

AuxBatOn
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Re: IFR Alternate

Post by AuxBatOn »

500+300=800 so 800 ft ceilings and 2 1/4 SM vis. Sliding scale not applicable.
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Caterpillar
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Re: IFR Alternate

Post by Caterpillar »

Why is there a lot of people saying that if you use 800, you don't use the HAT vis, and just use the standard (2sm)?
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Big Pistons Forever
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Re: IFR Alternate

Post by Big Pistons Forever »

Before using the sliding scale I would suggest you ask what weather phenomena is making the vis poor enough so that you can't just use the straight 800 and 2. Just because you can use the sliding scale doesn't mean it is a good idea....

Also personally as a general rule I would rather have a low ceiling but good vis underneath over a higher ceiling with crap vis
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Caterpillar
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Re: IFR Alternate

Post by Caterpillar »

What I mean is in this case, it gives 800-2 1/4.

Why lots of people are saying they can use 800-2? Their argument is "the ceiling is standard, therefore you can use the standard visibility".

Lots of airports with LNAV have 500-1 1/4 for mins, making them non-standard...
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iflyforpie
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Re: IFR Alternate

Post by iflyforpie »

You have to add the one mile visibility if the advisory vis is greater than one mile, since its 2 miles or one mile higher than the advisory vis, whichever is greater. Typically the advisory vis is the distance where youd get visual to land at MDA for a reasonable profile down to the runway. It’s typically going to be over a mile advisory vis on non precision approaches until you have minimums below 500 AAE at places where there are high intensity approach lights.
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triplebarrel
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Re: IFR Alternate

Post by triplebarrel »

It's a NPA so you have 800-2 or 300-1 above the lowest usable HAT/HAA. If it meets 800-2 then the following (sliding scale minima) are also authorized: 900-1.5 or 1000-1. In this case, you have 800 and 2.25 so it does meet the "Standard Alternate Minima" Therefore, in my opinion, you can use the sliding scale.
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sfostersa
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Re: IFR Alternate

Post by sfostersa »

So the thing it seems most of you are missing is that you have to pick the rule or combination of the two rules that gives you the more restrictive result. If your HAT for example was 400 and 1 and you added 300 and one to it you would come up with 700 and 2. The requirement does not then become 700 and 2 because the 800 and 2 rule is more restrictive in this example. In the example originally inquired about (500 and 1 1/4) adding 300 and 1 to it gives you 800 and 2 1/4. It is more restrictive than 800 and 2 there by 800 and 2 1/4 is the answer. ALWAYS PICK THE MORE RESTRICTIVE product of the two rules for ceiling and vis. Last ex. 400 and 1 1/4. at first you might think the answer is 700 and 1 1/4. But that would be incorrect it is 800 and 2 1/4. Again 800 and 2 1/4 is the most restrictive outcome of both rules. So also no sliding rule can be used for this and the the original problem.
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goingnowherefast
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Re: IFR Alternate

Post by goingnowherefast »

Where are some of you coming up with this stuff? Always round the the higher value. SFOSTERSA is really the first person to get this right. I'm also with Big Pistons Forever, I hate the sliding scale even when it does work.
triplebarrel wrote:
Wed Nov 13, 2019 9:40 pm
It's a NPA so you have 800-2 or 300-1 above the lowest usable HAT/HAA. If it meets 800-2 then the following (sliding scale minima) are also authorized: 900-1.5 or 1000-1. In this case, you have 800 and 2.25 so it does meet the "Standard Alternate Minima" Therefore, in my opinion, you can use the sliding scale.
Lets use that example again to explain why it's dumb. The approach is 500 - 1 1/4. Add the 300-1, and it becomes 800 - 2 1/4. If by some illogical brain fart in TC, that was allowed to be used as "standard", and the sliding scale applied, that would slide to ultimately 1000-1, which is BELOW the advisory visibility for the approach. The alternate minimums would therefor be below the published advisory visibility. There's no f**kin way that's allowed.
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iflyforpie
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Re: IFR Alternate

Post by iflyforpie »

If your calculated visibility is above 2, sliding scale does not apply.

Personally, in my opinion, I’ve never had an issue with sliding scale. I’ve used it a few times to fulfil legal requirements with a few caveats. Things like having a multitude of better alternates just beyond planned fuel range outside of reserve and good weather at my destination. 45 minutes can take you quite a few places depending on the aircraft and the geographical location and you can reduce power settings to climb higher to bring fuel burns down. Remember, these are alternate minima and advisory visibilities.

On an NPA with an ops spec you can use 50% of advisory vis to shoot the approach. If your alternate and approach ban is based on an LNAV approach but you’re shooting it to LPV minimums, you certainly can get in in many cases.

The other side of the coin is relying too much on alternate minima. I’ve seen a NSW SKC P6SM turn into 01003 1/4SM R15/1400D FZFG VV002 with a TAF AMD issued shortly thereafter. No wind, no ceiling, and a low temperature dewpoint spread is ripe for fog.
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triplebarrel
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Re: IFR Alternate

Post by triplebarrel »

goingnowherefast wrote:
Thu Nov 14, 2019 6:44 am
Where are some of you coming up with this stuff? Always round the the higher value. SFOSTERSA is really the first person to get this right. I'm also with Big Pistons Forever, I hate the sliding scale even when it does work.
triplebarrel wrote:
Wed Nov 13, 2019 9:40 pm
It's a NPA so you have 800-2 or 300-1 above the lowest usable HAT/HAA. If it meets 800-2 then the following (sliding scale minima) are also authorized: 900-1.5 or 1000-1. In this case, you have 800 and 2.25 so it does meet the "Standard Alternate Minima" Therefore, in my opinion, you can use the sliding scale.
Lets use that example again to explain why it's dumb. The approach is 500 - 1 1/4. Add the 300-1, and it becomes 800 - 2 1/4. If by some illogical brain fart in TC, that was allowed to be used as "standard", and the sliding scale applied, that would slide to ultimately 1000-1, which is BELOW the advisory visibility for the approach. The alternate minimums would therefor be below the published advisory visibility. There's no f**kin way that's allowed.
Thanks for putting that more into perspective, you are right super dumb to think that. I guess the wording screwed me up as I kept re-reading it form the cap gen
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