When do you convert RVR to visibility
 

Ladies and Gents,my question is when do you convert RVR to visiblity or VIS to RVR?

Runway Visual Range (RVR) measured by a transmissometer defines the distance one can see down the centerline of the runway. It is one of the main criteria used to determine the instrument approach minima. The maximum RVR measured is 2000 meters and no conversion to visibility is made. As long as the published approach RVR for a given runway is met an instrument approach can be made down to the D.H. and a landing carried out. :ok:

You can convert met viz to RVR .... if there are no RVR readings taken at the airport you are flying in/out of.

Think it's something like met viz x 1.5 will give you your equivalent RVR figure for day time ... and x 2.0 for night ??

Anyone else know the exact details ???

Firstly, met visibility may not be converted to RVR when RVR reports are available, and nor may it be used for calculating take off minima or CAT II or CAT III minima.

Secondly, the conversion depends upon day or night, and also the lighting facilities:

High Intensity approach & runway lighting
RVR = met vis x 1.5 (daytime), met vis x 2.0 (night time)

Any other lighting facilities
RVR = met vis x 1.0 (daytime), met vis x 1.5 (night time)

No lighting
RVR = met vis x 1.0 (daytime). Cannot be converted at night.


I have no idea why anybody would want to convert RVR to met visibility.

On the (new) Jepp plates we have instead of the normal RVR section some plates have the three letter acronym CMV and its not decoded in the Jepp supplement My guesstimate for CMV is Calculated Met Viability Can anyone correct this assumption

Splitting hairs I know but just cos the machine says the RVR is above the minima there is no guarantee of actually getting and maintaining the required visual references at the bottom of the approach.

Splitting Hairs!
 

Good point Daysleeper - and while we are on the subject (of splitting hairs) - the transmissometers (for there are normally three at any significant airfield) sit in the grass to one side of the r/w about 25m away from the c/l so they don't actually measure viz on the c/l. In shallow drifting fog this can be a right royal pain in the bum!

The original post/er seems a little confused/confusing..?
Care to expand upon the question?

OK - back in box...

Why would anyone need to convert RVR to vis anyway?

For a circling approach, when met visibility was unavailable due to the official weather observer being on a tea break.
Yes...it can happen in Africa.:}

Coupla points.

IRVR Equipment now can associate calculations to the centreline lights at 300m, edge lights otherwise -except in the UK where only edge lights figure in the algorithms.

Also, there is a massive downgrade of AGL performance within the calcs to account for degraded lamp performance.

So, when you next make an approach in LVOs and the RVR is OK, but you don't see the lights it might be 'cos the system has not been maintained to standard and therefore punches below its weight.

Oh, and a lamp is us when it falls to 50% of rated output - so you can still see them as you drive down the runway. Tricky things lights.

Sir George Cayley

RVR to visiblity or VIS to RVR
 

Thanks folks for all the knowledge banks

TAF says 400m vis for your destination with ILS, mim 550R, only 1 suitable alternate avaliable, can you go? Ab-so-lutely.

There's conversion for you.