Narrative:

While on approach to the montreal airport, the tower visibility and RVR fluctuated widely due to areas of thick fog moving across the airport. After initially being cleared for the localizer/back course to runway 6R, the visibility dropped below those minimums. However, the RVR for runway 6L improved from 1000 ft to 6000 ft, and an ILS approach was approved to runway 6L (which has approach minimums of 2600 ft RVR). After being cleared for the ILS to runway 6L, aircraft was on the localizer and descending on the GS, at approximately 2000 ft MSL, tower advised that the runway 6L RVR was now 1800 ft. Since we were on the final approach segment (aircraft descending on GS, below the GS intercept altitude of 2500 ft) the approach was continued. At decision ht the runway was visible and the landing was made. Later I realized that the final approach segment for canadian airports begins at the final approach fix, in this case at 'birpo.' the approach should have been discontinued since the below minimums report was received prior to birpo. With the large number of xboarded flts between the united states and canada, there should be commonality of all approach definitions and terms. My situation fell between the united states definition (2500 ft MSL) and the canadian definition (birpo fix) of the final approach segment. The final approach of an ILS should be free from these conflicting definitions.

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Original NASA ASRS Text

Title: CAPT OF AN LGT CONTINUED AN INST APCH AFTER RECEIVING BELOW MINIMUMS RPT PRIOR TO THE FINAL APCH FIX.

Narrative: WHILE ON APCH TO THE MONTREAL ARPT, THE TWR VISIBILITY AND RVR FLUCTUATED WIDELY DUE TO AREAS OF THICK FOG MOVING ACROSS THE ARPT. AFTER INITIALLY BEING CLRED FOR THE LOC/BACK COURSE TO RWY 6R, THE VISIBILITY DROPPED BELOW THOSE MINIMUMS. HOWEVER, THE RVR FOR RWY 6L IMPROVED FROM 1000 FT TO 6000 FT, AND AN ILS APCH WAS APPROVED TO RWY 6L (WHICH HAS APCH MINIMUMS OF 2600 FT RVR). AFTER BEING CLRED FOR THE ILS TO RWY 6L, ACFT WAS ON THE LOC AND DSNDING ON THE GS, AT APPROX 2000 FT MSL, TWR ADVISED THAT THE RWY 6L RVR WAS NOW 1800 FT. SINCE WE WERE ON THE FINAL APCH SEGMENT (ACFT DSNDING ON GS, BELOW THE GS INTERCEPT ALT OF 2500 FT) THE APCH WAS CONTINUED. AT DECISION HT THE RWY WAS VISIBLE AND THE LNDG WAS MADE. LATER I REALIZED THAT THE FINAL APCH SEGMENT FOR CANADIAN ARPTS BEGINS AT THE FINAL APCH FIX, IN THIS CASE AT 'BIRPO.' THE APCH SHOULD HAVE BEEN DISCONTINUED SINCE THE BELOW MINIMUMS RPT WAS RECEIVED PRIOR TO BIRPO. WITH THE LARGE NUMBER OF XBOARDED FLTS BTWN THE UNITED STATES AND CANADA, THERE SHOULD BE COMMONALITY OF ALL APCH DEFINITIONS AND TERMS. MY SIT FELL BTWN THE UNITED STATES DEFINITION (2500 FT MSL) AND THE CANADIAN DEFINITION (BIRPO FIX) OF THE FINAL APCH SEGMENT. THE FINAL APCH OF AN ILS SHOULD BE FREE FROM THESE CONFLICTING DEFINITIONS.

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.