Charles Oppermann wrote:

Something that bugs me is that
the ILS for 31C requires RVR of 4000 or 3/4 of mile visibility. The METAR
from just before the accident pegged visibility at 1/2 mile. Seems to me
that the approach shouldn't have even started.

Possibly.

However, the RVR report is not the same as prevailing visibility
reported in the METAR. It's not unusual for the two to be quite
different when there is a reduced visibility condition on or near the
airport.



Jack