Visual assessment of visibility at minima (using complicated arithmetic nonetheless) is not required to descend below DA/MDA. Having visual reference on one of the 11 or so listed items (als/thrshold lights/etc) is.
Granted, the wording on the website is misleading and could easily be misinterpreted, but this is basic IR stuff.
I suppose they are really trying to give you a (clever?) method of "estimating" visibility based on the ALS properties, so you can look smart to the Capt and say "yeah, looks like we have 2635' of visibility".
ok, later edit:
after reading that whole page one more time: It is definitely written in a way that suggests visibility at minima is a requirement before descent.
At least in EASA-land,regs make this a bit less ambigous:
" CAT.OP.MPA.305 (d) If, after passing 1 000 ft above the aerodrome, the reported RVR/VIS falls below the applicable minimum, the approach may be continued to DA/H or MDA/H "
" CAT.OP.MPA.305 (e) The approach may be continued below DA/H or MDA/H and the landing may be completed provided that the visual reference adequate for the type of approach operation and for the intended runway is established at the DA/H or MDA/H and is maintained."
Kinda happy to have found this, as it is probably the only time I have ever seen EU-OPS be easier to understand than FAR !!
Last edited by Radu Poenaru; 11th Dec 2015 at 08:26.