Factored Met Viz RVR's At Planning Stage?

[noblues]

Is it legal (in JAR/PAN ops) to use factored met viz from TAF's for the selection of alternates/diversion aerodromes?

[RYR-738-JOCKEY]

Nope. Not at planning stage. Not for T/O. Not if the plate has a RVR minimum. And not for circling approaches. Rgds.

[noblues]

Thanks RYR ... Maybe an added saftey margin to not allow it?

Quoted RVR is always much more than met viz ... makes using TAF data much more restrictive at planning stage ..

When you say
Not if the plate has a RVR minimum
I gues you mean for CATII or III ...

[Bbow]

Hmm...good question.
JAR-OPS states that you can not use converted viz to RVR for:
- take-off minima calculation
- CAT 2/3 minima
- or when a reported RVR is available.

in all other cases I think you can, planning or inflight...

Or did I miss something?

Anybody got a JAR-OPS reference? I looked at JAR-OPS Section 1 - Part E

Also, circling approaches are as far as I know based on met viz anyways...so no RVR conversion required.

[bookworm]

Nope. Not at planning stage.

Huh? What else can one use at the planning stage? TAFs forecast met visibility, not RVR. You must use that met vis against minimum RVR.

[RYR-738-JOCKEY]

Yes, you check forecasted Vis against minimum RVR. But unfactored. I can't find any references to JAR, but that's our company policy , anyway.

[bookworm]

Ah, I'm sorry, I understand what you were saying. "Nope" meant "use them unfactored". Obviously I can't speak for your company policy and conservatism is to be applauded. But I think JAR-OPS 1 permits the values to be factored:

Appendix 1 to JAR-OPS 1.430 (h) Conversion of Reported Meteorological Visibility to RVR
(1) An operator must ensure that meteorological visibility to RVR conversion not used for calculating take-off minima, Category II or III minima or when a reported RVR is available.

Note: If the RVR is reported as being above the maximum value assessed by the aerodrome operator, e.g. “RVR more than 1 500 metres”, it is not considered to a reported RVR in this context and the Conversion Table may be used.

(2) When converting meteorological visibility to RVR in all other circumstances than
those in sub-paragraph (h)(1) above, an operator must ensure that the following Table is used:

Planning minima don't fall under para 1, so I think you can use the table according to para 2

[Empty Cruise]

Bookworm,

I think the word you need to look at is: "...Conversion of reported meteorological visibility to RVR".

A reported visibilty can only be what is reported from the relevant ATC unit, in a METAR or in a SPECI. A TAF is - as the word implies - a forecast. Therefore, FCST viz > Min. RVR/visibility = go, FCST viz < Min. RVR/visibility = no-go (or go with 2 alternates in case of destination).

Hope this helps,
Empty

[bookworm]

Empty Cruise

Though I have to credit you with the correct observation of the word "reported" in the title, it doesn't change my opinion.

Met visibility and RVR are two different quantities and you can't simply compare one to the other as if equivalent. JAR-OPS 1 divides the circumstances into two:

1) those in which a met vis to RVR conversion is not permitted at all
and
2) those in which met vis (and the text, as opposed to the title, does not use the word "reported") is factored according to the conversion table.

There are no circumstances in which met vis should be compared with RVR by simply ignoring the factors in the table or pretending that they are all 1.