Narrative:

The WX was marginal VFR when we left bdr. The visibility reported as variable to 2 1/2 mi at bwi. We had left bwi for bdr at XA30. I didn't think bwi was going to go down--they had 15 mi visibility when we left. We came into bwi from kenton VOR (east) and were turned over to bwi approach control. I was told, 'the prevailing visibility was 1 mi, could I accept an ILS to runway 10?' I said, 'affirmative.' the first officer had gotten the ATIS and for some reason, possible the checklist he was doing plus he had only 2 or 3 weeks of line experience, I didn't get the contents of ATIS. We were turned over to the next controller who was vectoring us for the approach. We flew past the north side of the airport on downwind and I could see the field which had patchy fog over it. I asked for the visibility again and it was reported as 1/4 mi RVV on runway 15R and variable 1400 RVR on runway 10 with prevailing visibility of 1 mi. I didn't know which would be controling. Medium large transport were landing on runway 10, which is a CAT ii runway. As I was turned back on the localizer after being vectored through it for spacing I told the final controller I had a visibility on the runway and would take it visibility from there (approximately 2 mi outside facsimile). I was turned over to tower and reported in as 'visibility.' I was given an RVR of 1200' and cleared to land. All the runway was visible, including the first 2000-3000', but the center portion was harder to see. The fog was thicker there. I wasn't, and I'm still not, clear as to what the controling visibility was, prevailing RVR or my own view? I would have had not doubt if I would have been told the RVR was 1400' or visibility wasn't 1/2 mi. 'RVR 1800 or 1/2 mi' is on the approach plate. What confused me was 'prevailing' visibility. As I was cleared to land and approximately 2 mi from takeoff, the tower reported 15R RVR to an air carrier as either 3/4 or 1 1/4 mi, I can't remember which. I started to ask for a visibility to that runway, but I didn't. Would you please tell me if I did the wrong thing by landing on runway 10?

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Original NASA ASRS Text

Title: REQUESTED A VISUAL APCH WHEN RVR FOR THE RWY REPORTER AS 1200.

Narrative: THE WX WAS MARGINAL VFR WHEN WE LEFT BDR. THE VISIBILITY RPTED AS VARIABLE TO 2 1/2 MI AT BWI. WE HAD LEFT BWI FOR BDR AT XA30. I DIDN'T THINK BWI WAS GOING TO GO DOWN--THEY HAD 15 MI VISIBILITY WHEN WE LEFT. WE CAME INTO BWI FROM KENTON VOR (E) AND WERE TURNED OVER TO BWI APCH CTL. I WAS TOLD, 'THE PREVAILING VISIBILITY WAS 1 MI, COULD I ACCEPT AN ILS TO RWY 10?' I SAID, 'AFFIRMATIVE.' THE F/O HAD GOTTEN THE ATIS AND FOR SOME REASON, POSSIBLE THE CHKLIST HE WAS DOING PLUS HE HAD ONLY 2 OR 3 WKS OF LINE EXPERIENCE, I DIDN'T GET THE CONTENTS OF ATIS. WE WERE TURNED OVER TO THE NEXT CTLR WHO WAS VECTORING US FOR THE APCH. WE FLEW PAST THE N SIDE OF THE ARPT ON DOWNWIND AND I COULD SEE THE FIELD WHICH HAD PATCHY FOG OVER IT. I ASKED FOR THE VISIBILITY AGAIN AND IT WAS RPTED AS 1/4 MI RVV ON RWY 15R AND VARIABLE 1400 RVR ON RWY 10 WITH PREVAILING VISIBILITY OF 1 MI. I DIDN'T KNOW WHICH WOULD BE CTLING. MLG WERE LNDG ON RWY 10, WHICH IS A CAT II RWY. AS I WAS TURNED BACK ON THE LOC AFTER BEING VECTORED THROUGH IT FOR SPACING I TOLD THE FINAL CTLR I HAD A VIS ON THE RWY AND WOULD TAKE IT VIS FROM THERE (APPROX 2 MI OUTSIDE FAX). I WAS TURNED OVER TO TWR AND RPTED IN AS 'VIS.' I WAS GIVEN AN RVR OF 1200' AND CLRED TO LAND. ALL THE RWY WAS VISIBLE, INCLUDING THE FIRST 2000-3000', BUT THE CENTER PORTION WAS HARDER TO SEE. THE FOG WAS THICKER THERE. I WASN'T, AND I'M STILL NOT, CLEAR AS TO WHAT THE CTLING VISIBILITY WAS, PREVAILING RVR OR MY OWN VIEW? I WOULD HAVE HAD NOT DOUBT IF I WOULD HAVE BEEN TOLD THE RVR WAS 1400' OR VISIBILITY WASN'T 1/2 MI. 'RVR 1800 OR 1/2 MI' IS ON THE APCH PLATE. WHAT CONFUSED ME WAS 'PREVAILING' VISIBILITY. AS I WAS CLRED TO LAND AND APPROX 2 MI FROM TKOF, THE TWR RPTED 15R RVR TO AN ACR AS EITHER 3/4 OR 1 1/4 MI, I CAN'T REMEMBER WHICH. I STARTED TO ASK FOR A VIS TO THAT RWY, BUT I DIDN'T. WOULD YOU PLEASE TELL ME IF I DID THE WRONG THING BY LNDG ON RWY 10?

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.