In article , Charles Oppermann
wrote:

The FAA accident report has the following for the weather:

0115 11007KT 1/2SM SN FZFG VV003 M04/M05 A3006 R31C/4500V500

This doesn't appear properly formatted, as with a V separator, it's supposed
to be minimum and maximum. It's possible that it's supposed to be a minimum
of 4,500 and a maximum of 5,000 feet, and the extra zero was dropped off.

That's incorrect -- it's not minimum to maximum. It's 4500, variable
to 500. In the ops specs for every airline operation with which I'm
familiar, including my current 121 airline, the "variable" portion is
advisory only. So as far as weather for starting the approach, it was
4500.

It'll be interesting to get the CVR and ATC transcripts and find out what
the pilots were told.

Yep. If the tower gave them a more up-to-date RVR (which is pretty
likely), that's controlling over the sequence weather you posted above.

Second, Southwest's 737-700 airplanes have a heads-up display that lets
them use 3000 RVR on that runway at MDW.

Interesting! Do you any additional info on that?

I don't have much info beyond that, specific to SWA. The HUD is an
option on the next-generation 737s, and many of SWA's are so-equipped.
It's a real safety enhancement in low visibility. (That should also
discredit the notion that the airline skimps on safety equipment -- it
doesn't.)

Here's a picture of it in one of their cockpits:
http://www.airliners.net/open.file/868375/L/