PLT OF C402C LANDS AT HYA WHERE RPTED WX MINIMA IS BELOW MINIMUMS.

Narrative

I LEFT NANTUCKET FOR HYANNIS; MA; ON A SCHEDULED PAX FLT; PLTING A C402C. THE ATIS WAS CALLING HYA AS 200 FT OVCST AND 2 MI VISIBILITY. THE ILS RWY 24 HYA WAS IN USE REQUIRING AN RVR OF 5000 FT. AS APCH CTL TURNED ME OVER TO THE TWR JUST OUTSIDE THE OM; I CHKED IN AND TWR INFORMED ME THAT THE VISIBILITY WAS DETERIORATING RAPIDLY AND THE RVR WAS 3000 FT. I ACKNOWLEDGED AND CONTINUED THE APCH AND LNDG WITHOUT INCIDENT. I WAS WRONG IN CONTINUING WITH THE APCH PAST THE OM BECAUSE THE REQUIRED VISIBILITY ON THE RVR WAS BELOW MINIMUMS. IT HAD BEEN A DAY OF SEVERAL LOW APCHS IN ACK REQUIRING ONLY 1800 FT RVR; SO THE 3000 FT RVR SEEMED LIKE NO PROB. AFTER LNDG; THE TWR ASKED FOR MY FLT CONDITIONS ON APCH; AND I RPTED SEEING THE LIGHTS AT 400 FT AND ABOUT 1 MI VISIBILITY. THE NEXT PLT CHKED IN. THE TWR GAVE HIM THE SAME 3000 FT RVR RPT. HE ADVISED HE WAS NOT ABLE TO ACCEPT THE APCH AND REQUESTED THE ILS RWY 15 WITH ONLY 1/2 MI VISIBILITY REQUIRED. THAT IS WHAT I SHOULD HAVE DONE AS WELL. I HAVE DONE THIS APCH COUNTLESS TIMES BEFORE AND KNEW THAT 5000 FT RVR WAS THE MINIMUM VISIBILITY REQUIRED; HOWEVER; AT THAT PARTICULAR MOMENT IT DID NOT REGISTER IN MY MIND THAT IT WAS BELOW MINIMUMS. I WILL DEFINITELY BE MORE VIGILANT WHEN GETTING RPTS FROM THE TWR.