Narrative:

While being radar vectored to runway 3R at dtw, visibility was reported as 3/4 mi with runway 3R RVR 4500 ft. We were then changed to runway 3L at dtw with no reports of lower RVR for runway 3L. We were switched to dtw tower once past the OM and below the GS intercept altitude on the localizer and GS. Tower then reported runway 3L RVR 1400 ft. The runway 3L approach procedure requires 1800 ft RVR. We informed the tower we needed 1800 ft RVR to land. Tower then reported runway 3L touchdown zone RVR 1400 ft, midpoint RVR 2200 ft, rollout RVR 2000 ft. We continued the approach and had the runway in sight at 400 ft AGL and therefore landed with no incident. After landing we evaluated the situation and decided we should not have landed because the touchdown zone RVR is controling. I believe this situation wouldn't have occurred if we were given an earlier report of the low RVR on runway 3L. If we had received a report prior to the OM/GS intercept altitude, we would not have been able to start the approach to runway 3L. The dtw ATIS had no RVR reports and while originally being vectored to runway 3R the RVR was reported well above landing minimums. We did not receive any indication of the low RVR for runway 3L until on the approach inside the OM. This is the most critical phase of flight and when crew workload is at its highest.

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Original NASA ASRS Text

Title: ACR LTT CREW QUESTIONS LEGALITY OF IAP ILS APCH AFTER RWY CHANGE AND RPTED RVR IS LOWER AFTER THE LOM, FAF.

Narrative: WHILE BEING RADAR VECTORED TO RWY 3R AT DTW, VISIBILITY WAS RPTED AS 3/4 MI WITH RWY 3R RVR 4500 FT. WE WERE THEN CHANGED TO RWY 3L AT DTW WITH NO RPTS OF LOWER RVR FOR RWY 3L. WE WERE SWITCHED TO DTW TWR ONCE PAST THE OM AND BELOW THE GS INTERCEPT ALT ON THE LOC AND GS. TWR THEN RPTED RWY 3L RVR 1400 FT. THE RWY 3L APCH PROC REQUIRES 1800 FT RVR. WE INFORMED THE TWR WE NEEDED 1800 FT RVR TO LAND. TWR THEN RPTED RWY 3L TOUCHDOWN ZONE RVR 1400 FT, MIDPOINT RVR 2200 FT, ROLLOUT RVR 2000 FT. WE CONTINUED THE APCH AND HAD THE RWY IN SIGHT AT 400 FT AGL AND THEREFORE LANDED WITH NO INCIDENT. AFTER LNDG WE EVALUATED THE SIT AND DECIDED WE SHOULD NOT HAVE LANDED BECAUSE THE TOUCHDOWN ZONE RVR IS CTLING. I BELIEVE THIS SIT WOULDN'T HAVE OCCURRED IF WE WERE GIVEN AN EARLIER RPT OF THE LOW RVR ON RWY 3L. IF WE HAD RECEIVED A RPT PRIOR TO THE OM/GS INTERCEPT ALT, WE WOULD NOT HAVE BEEN ABLE TO START THE APCH TO RWY 3L. THE DTW ATIS HAD NO RVR RPTS AND WHILE ORIGINALLY BEING VECTORED TO RWY 3R THE RVR WAS RPTED WELL ABOVE LNDG MINIMUMS. WE DID NOT RECEIVE ANY INDICATION OF THE LOW RVR FOR RWY 3L UNTIL ON THE APCH INSIDE THE OM. THIS IS THE MOST CRITICAL PHASE OF FLT AND WHEN CREW WORKLOAD IS AT ITS HIGHEST.

Data retrieved from NASA's ASRS site as of July 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.