Originally Posted by
oggers
Soncibum says:
Maybe, but in Europe it is not permitted to convert the met visibility to RVR when the RVR minimum is less than 800m according to CAT.OP.MPA.110 AMC10. The implications of this rule could be discussed at length but as far as answering the OP is concerned it is a moot point because in his company:
Furthermore...
...these two things imply to me that the OP needs 2 alternates for dispatch because the forecast visibility is below the quoted Cat 1 vis of 800m and it is not permitted to convert it to equivalent RVR for the purposes of dispatch planning.
oggers,
(a) A conversion from meteorological visibility to RVR/CMV should not be used:
(1) when reported RVR is available;
(2) for calculating take-off minima; and
(3) for any RVR minima less than 800 m.
point 3) in intended after a conversion i.e. with a Vis of 400 m and a conversion factor of 2.0 you would get a CMV of 800m, but with, let's say a min RVR of 550 you could not do the conversion with a Visibility of, let's say 300m.