Narrative:

The WX at dca was foggy and the visibility was reported as variable between 800-1600 RVR. CAT ii approachs were being flown to runway 1. On the downwind for the approach while being radar vectored; potomac approach control reported the RVR as being unreliable on several occasions. They reported the tower visibility as variable between 1/2 and 1 mi. We were cleared for the approach and were told that the tower could see most of the runway. When checking in with the tower; they issued a landing clearance and reported the current RVR; which was below the required minimum. At approximately 3 NM and at 500 ft AGL; we broke out of the clouds and could see the entire runway. After landing I questioned the ground controller about the RVR reading and he responded that they were located close to the potomac river and did not always accurately indicate the visibility. Since the approach controller had reported several times that the RVR readings were unreliable; I found it puzzling why the local controller would continue to issue these readings to landing aircraft.

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Original NASA ASRS Text

Title: FLT CREW OF B737-400 RPT RVR READINGS AT DCA WERE THOUGHT TO BE INACCURATE YET WERE BEING RPTED TO ARRIVING ACFT. TWR CITES PROX TO POTOMAC RIVER AS KNOWN TO PRODUCE FALSE READINGS.

Narrative: THE WX AT DCA WAS FOGGY AND THE VISIBILITY WAS RPTED AS VARIABLE BTWN 800-1600 RVR. CAT II APCHS WERE BEING FLOWN TO RWY 1. ON THE DOWNWIND FOR THE APCH WHILE BEING RADAR VECTORED; POTOMAC APCH CTL RPTED THE RVR AS BEING UNRELIABLE ON SEVERAL OCCASIONS. THEY RPTED THE TWR VISIBILITY AS VARIABLE BTWN 1/2 AND 1 MI. WE WERE CLRED FOR THE APCH AND WERE TOLD THAT THE TWR COULD SEE MOST OF THE RWY. WHEN CHKING IN WITH THE TWR; THEY ISSUED A LNDG CLRNC AND RPTED THE CURRENT RVR; WHICH WAS BELOW THE REQUIRED MINIMUM. AT APPROX 3 NM AND AT 500 FT AGL; WE BROKE OUT OF THE CLOUDS AND COULD SEE THE ENTIRE RWY. AFTER LNDG I QUESTIONED THE GND CTLR ABOUT THE RVR READING AND HE RESPONDED THAT THEY WERE LOCATED CLOSE TO THE POTOMAC RIVER AND DID NOT ALWAYS ACCURATELY INDICATE THE VISIBILITY. SINCE THE APCH CTLR HAD RPTED SEVERAL TIMES THAT THE RVR READINGS WERE UNRELIABLE; I FOUND IT PUZZLING WHY THE LCL CTLR WOULD CONTINUE TO ISSUE THESE READINGS TO LNDG ACFT.

Data retrieved from NASA's ASRS site as of January 2009 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.