My understanding (and that of our CAA approved ops. manual) is that:
You may commence an approach regardless of the reported RVR but may not continue beyond the OM or equivalent position unless if the RVR is below minima. ie. approach ban.
Once past the OM if the RVR falls below minima the approach may be continued to MDA/DA/DH and IF required visual reference is established and maintained at that point you can land perfectly legally.
So basically once past the OM it's up to the commander and if you are visual at DH/DA you can land quite legally, a report may very well have to be filed but there is no proof that visual reference was not obtained and that the landing was illegal. If you were in a 2/3 crew aircraft you may well get reported, quite rightly, by the other crew members but they and you are the only ones who really know.
The situation is no different from ANY instrument approach, the tower may well be reporting a value much higher than minimum but due to the uneven nature of fog patches you may not see the runway at DA/DH so you go around. If you continue below DA and land you would have broken the law regardless of the reported vis.
In short, landing with reported vis. below the minima for the approach is NOT illegal, landing without the required visual reference at DA/DH most certainly is.
Our manual also has a note saying that visual approaches may not be conducted with the RVR less than 800m so in answer to orginal question my opinion is that if the reported RVR is less than 800m you can't start a visual approach. It is grey area though because once you have started one (inside OM?, what measure do we use? it's a visual after all) and the RVR falls below 800m what do you do?, if you can "maintain visual reference" there is no difference between that and the visual segment following an SRA or NDB that might terminate some way out at say 800ft. If you loose visual reference in either case you have to go-around and you could be well below MDA or DH when you do.
Anyone care to comment, can't find anything in my documents and manuals that covers it.
Last edited by Max Angle; 24th Nov 2005 at 14:14.