Narrative:

The bos sequence was partial observation ceiling 300-400', visibility 1/4-1/2 mi and RVR 4R 4000', variable 6000+. We were vectored for an ILS to 4R. During the approach we heard various RVR readings, the lowest of which was 3500', given a flight which needed 4500'. Shortly thereafter he was given 5000'. That was the last RVR I remember before our approach. We set up for an autoplt-autoland approach. When clearance for the approach we were not given an RVR, but were not concerned since all reports were well above our limits. After passing the OM at about 700', the tower controller gave us a report of 'tall ships in the harbor.' we reset our altitude bugs to 359' (tall ships DH) and at about 500' the first officer called 'approach lights.' between 500 and 400' we had runway environment. We determined visually that we had the required 1 mi visibility and continued to a successful autolndg. In retrospect there was some question as to the legality of continuing the approach under the circumstances. In any case, there are several things about this situation that are of concern safety-wise. First we were not given the current RVR along with the ships in harbor report. This puts the crew in the position of having to make a decision west/O all the pertinent information. I was about to ask for an RVR when we saw the lights and got runway environment. Second, I don't think it is appropriate to give that sort of report at that stage of a low visibility approach. The whole concept of the sterile cockpit is to keep unnecessary distrs out of the cockpit during INS approachs. I find it hard to believe that between our arrival at 700' and the landing of the aircraft 4 mi ahead of us that a large ship could suddenly pop-up in an position that would compromise the safety of our flight. One would think that with modern communications and considering the speed at which large ships move through congested harbors in bad WX, that if indeed a ship was going to pose a safety threat, it could be known prior to the flight's arrival at the OM, and the flight could be notified at that time. On the other hand, if through error or delayed communications the controller became aware that a real threat did exist, it would seem that the proper thing to do would be to instruct the aircraft to make a missed approach. Another gray area worth mentioning is that the tall ships minimums box is on the category I ILS approach plate, which leads us to believe that it is legal to reset bugs and continue a CAT I approach to tall ships DH, just as you would if a NAVAID or other component failed. However I haven't found anyone knowledgeable who completely sure that is true. If it is not legal to do so, then those minimums should either be on a different approach chart or there should be a note plainly stating that fact. The fact that bos is the only place I know of that has such a situation can sometimes lead to unnecessary confusion during the critical stages of an approach.

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Original NASA ASRS Text

Title: 3 REPORTS PROTEST TIMING OF TWR ADVISORY OF TALL SHIPS IN CHANNEL.

Narrative: THE BOS SEQUENCE WAS PARTIAL OBSERVATION CEILING 300-400', VISIBILITY 1/4-1/2 MI AND RVR 4R 4000', VARIABLE 6000+. WE WERE VECTORED FOR AN ILS TO 4R. DURING THE APCH WE HEARD VARIOUS RVR READINGS, THE LOWEST OF WHICH WAS 3500', GIVEN A FLT WHICH NEEDED 4500'. SHORTLY THEREAFTER HE WAS GIVEN 5000'. THAT WAS THE LAST RVR I REMEMBER BEFORE OUR APCH. WE SET UP FOR AN AUTOPLT-AUTOLAND APCH. WHEN CLRNC FOR THE APCH WE WERE NOT GIVEN AN RVR, BUT WERE NOT CONCERNED SINCE ALL RPTS WERE WELL ABOVE OUR LIMITS. AFTER PASSING THE OM AT ABOUT 700', THE TWR CTLR GAVE US A RPT OF 'TALL SHIPS IN THE HARBOR.' WE RESET OUR ALT BUGS TO 359' (TALL SHIPS DH) AND AT ABOUT 500' THE F/O CALLED 'APCH LIGHTS.' BTWN 500 AND 400' WE HAD RWY ENVIRONMENT. WE DETERMINED VISUALLY THAT WE HAD THE REQUIRED 1 MI VISIBILITY AND CONTINUED TO A SUCCESSFUL AUTOLNDG. IN RETROSPECT THERE WAS SOME QUESTION AS TO THE LEGALITY OF CONTINUING THE APCH UNDER THE CIRCUMSTANCES. IN ANY CASE, THERE ARE SEVERAL THINGS ABOUT THIS SITUATION THAT ARE OF CONCERN SAFETY-WISE. FIRST WE WERE NOT GIVEN THE CURRENT RVR ALONG WITH THE SHIPS IN HARBOR RPT. THIS PUTS THE CREW IN THE POS OF HAVING TO MAKE A DECISION W/O ALL THE PERTINENT INFO. I WAS ABOUT TO ASK FOR AN RVR WHEN WE SAW THE LIGHTS AND GOT RWY ENVIRONMENT. SECOND, I DON'T THINK IT IS APPROPRIATE TO GIVE THAT SORT OF RPT AT THAT STAGE OF A LOW VISIBILITY APCH. THE WHOLE CONCEPT OF THE STERILE COCKPIT IS TO KEEP UNNECESSARY DISTRS OUT OF THE COCKPIT DURING INS APCHS. I FIND IT HARD TO BELIEVE THAT BTWN OUR ARR AT 700' AND THE LNDG OF THE ACFT 4 MI AHEAD OF US THAT A LARGE SHIP COULD SUDDENLY POP-UP IN AN POS THAT WOULD COMPROMISE THE SAFETY OF OUR FLT. ONE WOULD THINK THAT WITH MODERN COMS AND CONSIDERING THE SPD AT WHICH LARGE SHIPS MOVE THROUGH CONGESTED HARBORS IN BAD WX, THAT IF INDEED A SHIP WAS GOING TO POSE A SAFETY THREAT, IT COULD BE KNOWN PRIOR TO THE FLT'S ARR AT THE OM, AND THE FLT COULD BE NOTIFIED AT THAT TIME. ON THE OTHER HAND, IF THROUGH ERROR OR DELAYED COMS THE CTLR BECAME AWARE THAT A REAL THREAT DID EXIST, IT WOULD SEEM THAT THE PROPER THING TO DO WOULD BE TO INSTRUCT THE ACFT TO MAKE A MISSED APCH. ANOTHER GRAY AREA WORTH MENTIONING IS THAT THE TALL SHIPS MINIMUMS BOX IS ON THE CATEGORY I ILS APCH PLATE, WHICH LEADS US TO BELIEVE THAT IT IS LEGAL TO RESET BUGS AND CONTINUE A CAT I APCH TO TALL SHIPS DH, JUST AS YOU WOULD IF A NAVAID OR OTHER COMPONENT FAILED. HOWEVER I HAVEN'T FOUND ANYONE KNOWLEDGEABLE WHO COMPLETELY SURE THAT IS TRUE. IF IT IS NOT LEGAL TO DO SO, THEN THOSE MINIMUMS SHOULD EITHER BE ON A DIFFERENT APCH CHART OR THERE SHOULD BE A NOTE PLAINLY STATING THAT FACT. THE FACT THAT BOS IS THE ONLY PLACE I KNOW OF THAT HAS SUCH A SITUATION CAN SOMETIMES LEAD TO UNNECESSARY CONFUSION DURING THE CRITICAL STAGES OF AN APCH.

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.