ALTERNATE WEATHER MINIMA REQUIREMENTS

[theabcman]

My question is about alternate weather requirements. I am self studying for the INRAT exam.

ONE USABLE PRECISION APPROACH 600-2* or 300-1 above the lowest usable HAT and visibility, whichever is greater.

whichever is greater? is that between the 600-2 or 300-1 above the lowest HAT and visibilty.... or is it just the 300-1 that you take the greater from?

lets say the ILS mins are 200-1/2 that means the minimum alternate requirements would be 500-11/2 or 600 - 2, so 600-2 is the greater is that correct?


Thanks for your time.




ALTERNATE WEATHER MINIMA REQUIREMENTS

FACILITIES AVAILABLE AT SUITABLE ALTERNATE WEATHER REQUIREMENTS
TWO OR MORE USABLE PRECISION APPROACHES, each providing straight-in minima to separate
suitable runways 400-1 or 200-1/2 above lowest usable HAT and visibility, whichever is greater.

ONE USABLE PRECISION APPROACH 600-2* or 300-1 above the lowest usable HAT and visibility, whichever is greater.

NON-PRECISION ONLY AVAILABLE 800-2* or 300-1 above the lowest usable HAT/HAA and visibility, whichever is greater.

NO IFR APPROACH AVAILABLE Forecast weather must be no lower than 500 ft above a minimum IFR altitude that will permit a VFR approach
and landing.


*600-2 and 800-2, as appropriate, are considered to be STANDARD ALTERNATE MINIMA.

[aileron]

Think more conservative, or self-preserving ie the higher limit would be 600 & 2. Of course if it's standard then you can slide the limits, ie 700 & 1 1/2 or 800 & 1.

Good luck on your exam!

[theabcman]

Great thanks for that!! it was driving me nuts trying to work out what they wanted!!!

[Tim]

dont forget you must take the highest of both hat and vis, so mix and match as required for the biggest number

[Alpha Crit]

Sometimes it's easier to think of the ceiling and vis separately. For example, for your situation of One Useable Precision Approach, think of it as:

Ceiling: 600 feet, or 300 feet above the lowest useable HAT, whichever is higher; and then

Vis: 2 miles, or 1 mile above the advisory vis for that approach, whichever is higher.

Remember also, if you do the math on the vis, and get a number greater than 3 miles, round down to 3 miles.

[swordfish]

When you start flying this IFR game, you should note that not ALL ILS approaches are 200/½ minimums. Some are occasionally higher than the ½-mile and occasionally higher than 200' - Inuvik ILS 06, for example.

The DH is limiting - not the visibility. i.e. you get down to 200' and you can see the landing environment well enough to continue visually, you are not constrained by the ½-mile vis. But if you can't see anything at 200', it's "Goodbye Charlie".

Also, on sliding the minima that aileron mentioned: you can only slide if you meet the standard criteria. For example, you cannot slide the 34 approaches at Red Deer.

Another thing to keep in mind is that for visibilities over 2 miles, they do not report ¼-mile increments. Let's say you are using Fort Simpson as an alternate for Fort Nelson, and you have to do a VOR/DME 31 - you will need 2½ miles in the TAF.

One last thing you will have to be cool on (i.e. understand it completely) is the approach ban stuff. There are different tables for 602 operations, 700 and 704 with the Ops Spec.

[Aviatard]

So, here's a dumb question. The alternate ceiling and visibility limits. When looking at the CAP GEN, it gives you 2PA, 1PA, No PA. Is that based on the airport as a whole, or just on the approach?

The reason I ask is sometimes, you'd only have 1 ILS up on a runway but not for the reciprocal runway (it's down). That would be 1 Precision Approach. But lets say you have LPV available. Is LPV a precision approach or is it not? Because if it is, then the minima for this airport goes from 1 PA, to 2 PA's. Then we're looking at 400-1 and 200-1/2

The rules for taking credit for LPV approaches are explained in the CAPGEN.

[CpnCrunch]

So, here's a dumb question. The alternate ceiling and visibility limits. When looking at the CAP GEN, it gives you 2PA, 1PA, No PA. Is that based on the airport as a whole, or just on the approach?

The reason I ask is sometimes, you'd only have 1 ILS up on a runway but not for the reciprocal runway (it's down). That would be 1 Precision Approach. But lets say you have LPV available. Is LPV a precision approach or is it not? Because if it is, then the minima for this airport goes from 1 PA, to 2 PA's. Then we're looking at 400-1 and 200-1/2

It says "separate suitable runways", so it can't be a reciprocal approach on the same bit of asphalt. There needs to be more than one runway at the airport, each with a precision approach.

[Crewbunk]

I have no earthly idea what "take credit for" means in that context. That sounds like an accomplishment. What is the accomplishment behind using an LPV? NONE

So why use that term?

You really do have no earthly idea do you? That’s probably why you posed a “dumb question”, (your term).

In fact, that’s exactly how it’s termed. As correctly stated, the rules for “taking credit” for approaches are in the CAPGEN, or whatever governance you use, like an airline FOM. The concept being that an LPV approach could “take credit” for the existence or requirement of a precision approach.

How many, and under what circumstances depends under what rules you are restricted. The general public could use the CAPGEN. (I use an airline FOM).

[photofly]

. The concept being that an LPV approach could “take credit” for the existence or requirement of a precision approach.

If we’re going to be snippy about terminology, one should write that it’s actually the pilot that takes credit for the existence of the precision approach.

[Crewbunk]

Hey if answering questions is too difficult for you, perhaps you should retire from the forums. Didn't mean to get you all worked up old man.

You asked the “dumb question”, we answered your “dumb question”.

Then …. you decided to mock how it’s (correctly) expressed. I hope you learned something.

[Aviatard]

So, here's a dumb question. The alternate ceiling and visibility limits. When looking at the CAP GEN, it gives you 2PA, 1PA, No PA. Is that based on the airport as a whole, or just on the approach?

The reason I ask is sometimes, you'd only have 1 ILS up on a runway but not for the reciprocal runway (it's down). That would be 1 Precision Approach. But lets say you have LPV available. Is LPV a precision approach or is it not? Because if it is, then the minima for this airport goes from 1 PA, to 2 PA's. Then we're looking at 400-1 and 200-1/2

The rules for taking credit for LPV approaches are explained in the CAPGEN.

I have no earthly idea what "take credit for" means in that context. That sounds like an accomplishment. What is the accomplishment behind using an LPV? NONE

So why use that term?

The “take credit” terminology is how it’s expressed in the CAPGEN. It means you can’t use the LPV minima in determining whether an airport would be a legal alternate. Instead you have to use the LNAV minima which are higher than LPV and therefore more conservative.

[Aviatard]

I was under the impression that LPV is precision approach to the destination. But not to the alternate.

I'm trying to understand the alternate minima requirements. But those minima change based on THE NUMBER of precision approaches available. I'm not really interested in the type of precision approach to be honest, but the number of approaches available. Is that based on the aerodrome as a whole or per approach?

To me, it wouldn't make sense for the alternate minima to be dependent on the approach because who's picking the alternate approach before they depart? Instead, dependent on the amount of precision approaches for the airport as a whole.

Does that make sense?

It's not just the number of approaches, it's the number of usable approaches. What makes an approach useable? There's probably more but here are a few things:
- do I have the equipment to do that approach?
- could I actually land on that runway? A B737 approach to a 3000 foot runway isn't going to work
- are the tailwind / crosswind components doable for my aircraft?
- if it's a ground based approach, is the approach in service? ILS equipment needs periodic maintenance and may be offline at the time you expect to arrive


Who's picking the alternate approach before they depart? You are. That's the entire point of alternates. Will I likely have an approach that I can use in case I have to proceed to an alternate? Since you can't count LPV minima, you can't count those as precision approaches. The only airports where you're likely to have two or more usable precision approaches is airports which have parallel runways. Having an ILS to both ends of the same piece of pavement probably doesn't work since on one of them you've likely got a tailwind.

[Aviatard]

I mean that's the whole reasoning behind alternate minima being for planning purposes only. You can't use the alternate if in your planning stages, it doesn't meet alternate minima requirements. However if it DOES meet standards during planning, but then on arrival, the ceiling is much lower than forecast (under minima), you're ALLOWED to land.

I am quite aware of the reasons for alternates. I just answered the questions you asked.