INFLT WX ENCOUNTER; SEVERE TURB. INJURIES. CAPT THOUGHT HE COULD PENETRATE A CIRRI LINE; BUT WAS CLOSED IN ONCE GOING THROUGH IT AND EXPERIENCED SEVERE TURB. RPTR FO WAS UNHAPPY WITH THE DECISION; BUT DIDN'T ADVOCATE STRONGLY.

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WE WERE ON A SCHEDULED PAX FLT BTWN FLL AND ATL. IT WAS LATE AFTERNOON IN THE SUMMER; WITH THE USUAL CONVECTIVE ACTIVITY IN FL. TO THE NW OF CRAIG VOR WAS A LINE OF TSTMS WE WOULD NEED TO GET THROUGH OR AROUND IN ORDER TO GET TO ATLANTA. THE LINE APPEARED TO EXTEND ABOUT 100 MI BEYOND OUR POS. WE HAD BEEN GIVEN CLRNC TO DEVIATE AS NECESSARY; DIRECT TO THE DUBLIN FIX ON THE ATL ARR WHEN ABLE. WE WERE AT FL370; APPROX .80 MACH; IN CLR AIR WITH LIGHT CHOP. THE SEAT BELT LIGHT WAS ON. THE CELLS WERE IMBEDDED IN CIRRIFORM CLOUDS; BUT OUR WX RADAR INDICATED A NARROW GAP BTWN 2 CELLS. THE CAPT (PF) BEGAN A TURN TOWARD THE GAP RATHER THAN END RUN THE LINE. WE STUDIED IT ON THE RADAR AND I ASKED HIM IF HE WAS GOING TO 'THREAD THAT NEEDLE.' I CONSIDERED THE 2 LARGE CELLS TO BE IN TOO CLOSE PROX; BUT HE ELECTED TO CONTINUE. ALTHOUGH I DID NOT THINK IT WAS A WISE DECISION; I SAID NOTHING MORE. PENETRATING THE CIRRUS I CALLED THE FLT ATTENDANTS ON THE INTERPHONE AND ADVISED THEM TO PREPARE FOR SOME TURB. BOTH CABIN SECTIONS ACKNOWLEDGED. WE BROKE INTO THE CLR BTWN THE 2 CELLS TO FIND ANOTHER CELL BUILDING RAPIDLY DIRECTLY IN OUR PATH. THERE WAS NO ROOM TO MANEUVER TO AVOID IT AND UPON PENETRATION WE ENCOUNTERED APPROX 30 SECONDS TO 1 MIN OF HVY TO SEVERE TURB; WITH ALT FLUCTUATIONS OF PLUS 400 TO MINUS 700 FT. ONCE CLR OF THE TURB WE HAD 3 FLT ATTENDANTS AND 1 PAX INJURED. WE LANDED IN ATL ABOUT 25 MINS LATER; WERE MET AT THE GATE BY PARAMEDICS AND THE INJURED PAX AND CREW MEMBERS WERE TREATED AND TRANSPORTED TO A LCL HOSPITAL. HUMAN FACTORS CONSIDERATIONS: THERE WAS NO NEED TO ATTEMPT PENETRATION OF THE LINE. A DEV AROUND THE END OF THE LINE WOULD HAVE COST NO MORE THAN 15 MINS ON OUR ARR TIME. I FELT IT UNWISE TO PENETRATE AT THE POINT THE CAPT HAD SELECTED; BUT CHOSE TO MAKE NOTHING MORE THAN A SMALL QUESTION ABOUT IT. OUR RAPPORT WAS GOOD; AND I BELIEVE HE WOULD HAVE RESPONDED WELL HAD I TOLD HIM OUTRIGHT OF MY MISGIVINGS. BUT I DID NOT WANT TO APPEAR PUSHY. PART OF MY JOB IS TO PROVIDE INPUTS; CHKS AND BALS. I FAILED IN THIS AREA AND ITS COST WAS SEVERAL PEOPLE INJURED (FORTUNATELY NOT SEVERELY); THE REST TERRIFIED (SEVERELY); AND AIRPLANE TAKEN OFF FLYING STATUS FOR MAINT INSPECTIONS AND REPAIRS; AND A LOT OF PAPERWORK. IT WASN'T WORTH IT.