ECON cruise, LR cruise...
Join Date: Apr 2002
Location: MIRSI hold - give or take...
Age: 52
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Visibility is different to CMV - it's generally used to obtain an 'RVR equivalent' when outside RVR range. The Aerodrome Meteorological Observation and Forecast Study Group (AMOFSG) 10th meeting, Agenda Item 5: Aerodrome observations: Inconsistency Between Visibility and CMV, a Converted Meteorological Visibility:
"Straight-in approach minima are often expressed in terms of RVR. Following widely used procedures, many airline operators convert the reported meteorological visibility into an equivalent RVR value, called CMV. This conversion is applied by the pilot only for landing, when the required RVR minimum is equal or above 800 m (1/2 sm) and when the RVR is not available (a reported RVR above its 2000 m limit is considered as being not available)."
Visibility is only used for those approaches that are not straight-in, ie offset more than 4˚ for Cat C/D, classed as side-step or circling. The credit for light sources differs - basically, in visibility reporting, only limited account is taken for looking at a light-source - very different from looking at a battery of approach lights.