UPON ENCOUNTERING DETERIORATING WX CONDITIONS DURING A VFR PAX FLT; FLT CREW OF HELI ENTER HYA CLASS D AIRSPACE WITHOUT CLRNC.

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I WAS PLT FLYING FROM RIGHT SIDE OF COCKPIT ON A VFR PAX FLT. FIRST LEG OF FLT WAS GOOD VFR UNTIL PAST PVD. THE WX BEGAN TO DETERIORATE TO LOWER THAN FORECAST CONDITIONS (WORST FORECAST WAS APPROX 800 AND 3; ACTUAL FELL TO ABOUT 300 AND 1.5). FALLBACK PLAN WAS TO PICK UP IFR CLRNC PAST NEW BEDFORD; AND CONTINUE TO CQX; BUT CAPT SEEMED RELUCTANT TO EXECUTE PLAN B ON ACCOUNT OF FUEL RANGE (NO FUEL AVAIL AT CQX); AND FEAR OF GETTING DELAYED BY ATC. I FAILED TO ADVOCATE STRONGLY FOR PLAN B BECAUSE OF FUEL CONCERNS; TARGET FIXATION; AND PAST HISTORY WITH THIS CAPT. WE TRANSITED FMH'S CLASS D IN CONTACT WITH LOCAL CTLR; THEN CALLED HYA TWR FOR SPECIAL VFR CLRNC THROUGH THEIR AREA. THEY DENIED US CLRNC AND TOLD US TO REMAIN CLR ON ACCOUNT OF INBOUND IFR TFC. WE CONTINUED SE BOUND TO THE SHORELINE; AND THEN TURNED EBOUND ABOUT A HALF MILE OFFSHORE TO PARALLEL THE SHORELINE. DISTANCE TO HYA WAS APPROX 7.5 MI ACCORDING TO FMS. AT THIS POINT THE CAPT DECIDED TO ESTABLISH CONTACT WITH CAPE APCH FOR ADVISORIES; AND SELECTED 'DIRECT TO' THE NEXT POINT (CQX) ON OUR FLT PLAN; SO I COULD NO LONGER READ 'COUNT DOWN' DISTANCE TO HYA ON MY EFIS DISPLAY. CAPE APCH IDENTED US AND STATED (ROUGHLY): 'RADAR CONTACT 2 MI W OF HYA HDG E.' AS MENTIONED; I WAS PF; NOT THE PLT ON THE MAP; BUT I DON'T BELIEVE THAT GEOMETRY IS POSSIBLE FOR AN ACFT OVER THE OCEAN S OF THE SHORELINE AND TRACKING E. I DO BELIEVE; HOWEVER; THAT WE PROBABLY PENETRATED THE SOUTHERN EDGE OF THE CLASS D AREA; AND MAY HAVE CLOSED WITHIN 3-4 NM OF HYA.