Is this the bit in JAR-OPS about calculating an equivalent RVR from the met vis if RVR is not available?
If so, I would suggest that there is little, if any, real relationship between the two values. It is simply a way of controlling whether an approach can be made or continued in poor visibility. As such, the conversion is is just an approximation rather than an attempt to relate the two (different) measuring systems in a real-world situation.
BTW, met vis is now reported in terms of prevailing visibility, at least that is the ICAO standard. The exact rules escape me for the moment but it means that the vis in a met report may not be the lowest in any direction.
PS - Just my understanding as a simple controller.
Last edited by Spitoon; 19th April 2007 at 16:38.