An Operator should ensure that a meteorological visibility to RVR conversion is not used for takeoff, for calculating any other required RVR minimum less than 800 m, for visual/circling approaches, or when reported RVR is available.
When converting meteorological visibility to RVR in all other circumstances than those in
sub-paragraph above, an operator should ensure that Table below is used:
The only time you can use converted visibility is:
a) No RVR measurement available and either
b) CAT I ILS, or
c) Straight-in NPA
Assume for the moment that you want to land somewhere and there is no RVR available. You only have the visibility of 275M at night with HI app lights.
Your minimums are 550m 300M mid-end and 300m stop-end.
Are you allowed to convert the visibility to 550RVR ? 275x2
So for take off you can't use CMV if the visibility is less than 800m but what about if
you are already in the air?