Yes, I'm talking about the approach ban. There is nothing to stop an aircraft commencing an approach. It could be 75m RVR on your CAT 1 runway - you
need 550m - but you can start an approach in the hope that the RVR will improve. However, the RVR must have improved by the time you reach 1000' ARTE (above runway threshold elevation). The outer marker or 4 miles are also usable as alternatives. If at the "approach ban" point (1000') the RVR is still below the required value - you MUST go around.
If the value is above required at 1000' - you can continue. If it falls below required RVR after you have passed the ban point, you can continue down to your applicable minima to land or go-around as required.
So on the incident in question is it highly likely that RVR was below required at the approach ban point so a go-around should have been executed....... breaking the sequence which lead to the subsequent events.
Clear?
A4