What to compare minima (DH and RVR) with?

[Kriekos]

Hi everyone,

Assume you're planning a flight and you need to check whether the WX at the destination at ETA +/- 1hr is above minimum DH and minimum RVR.
1. Where do you look to see if WX is better than min DH? Do you look at the clouds reported in the TAF? If yes, which clouds bring the WX below DH?
2. Where do you look to see if WX is better than min RVR? I believe TAFs give visibility but not RVR (RVR is given in METARs but a METAR have a limited validity).

To conclude: I know the theory about operating and planning minima and appointing alternates, but I don't know how to actually check if the minima are met at the aerodrome.

Thanks in advance for the help!

Grtz

[OhNoCB]

Use the TAF.

If you are looking at clouds it will be ceiling you are looking for ie. broken or overcast.

RVR is controlling in when it comes to actually making an approach, for planning use the forecast vis.

[Kriekos]

OhNoCB So to check if min DH is met you look at the cloud ceiling (more than 4 octa's) in the TAF, not cloud base (any octa)? Where do you look for RVR? Because TAF doesn't give RVR, only prevailing visibility.

[OhNoCB]

Correct, ceiling not cloud base.

You don't look for an RVR at planning stage, use the visibility.

[FlightDetent]

Kriekos your confusion is justified, many are. It is the small terminology that matters.

In general:

DH is typically associated with precision approach and for those the minima is expressed by RVR value only. For the ceiling you don't look at all. When the weather gets bad enough there will be an RVR value in the TAF, don't worry. Well, that is the point where you actually need to start worrying. :E

For NPA approaches, both VIS and ceiling requirements need to be satisfied, you know well how to work from there.

As experience, training, and opinions differ, I find the well intended guidance provided in #2 and #4 quite misleading.
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[Intrance]

When the weather gets bad enough there will be an RVR value in the TAF, don't worry. Well, that is the point where you actually need to start worrying. :E
​​​​​​Correct me if I'm wrong, but RVR is only an observation, never a forecast, right? You should not find RVR in any TAF. They might note a trend in the METAR though, eg. R18/0500U or 0500D etc. But as mentioned, that is of limited validity and not a proper forecast.

So I suppose a more complete answer would be;

#1: For non-precision approaches and your (M)DA, use the ceiling and/or vertical visibility predicted in the TAF. For precision approaches, don't even worry about your DA/DH as the RVR will be limiting factor.
#2: Since RVR is not reported in TAF, use the reported visibility for planning. If visibility is forecast as 500m and you need 550m RVR for your CAT1 ILS, you will likely be able to land but for planning purposes the airport is considered below minima and you may need a second alternate for example.

Hope I am pulling all this out of my brain correctly.

[FlightDetent]

Darn! Correct, much apologies. Did I have an easy winter so far. 😅

How does the VIS/RVR conversion table apply for the planning phase?

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[Theholdingpoint]

No CMV for flight planning (or 1.0 factor if you wish).

[Kriekos]

Intrance Theholdingpoint
So you can just use visibility from the TAF as an RVR? Without applying the CMV factors? Are you sure about that?
Seeing that the factors increase visibility to RVR/CMV it would be the safer way not to apply them...

[Theholdingpoint]

Yes.
https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/631x522/image_236f1f555428419c7378b4f84f09e47504b5e614.png

[Kriekos]

Theholdingpoint
Perfect! Much appreciated!