RPTR DEVIATED FOR WX THROUGH SAME GAP AS OPPOSITE DIRECTION SAME ALT TFC. FREQ CONGESTION DELAYED CTLR INTERVENTION. TCASII RA COMMANDS DSCNT TO RPTR FOLLOWED BY CTLR COMMANDS DSCNT TO OPPOSITE TFC. NMAC 300 FT VERT AND 500 FT HORIZ.

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OUR MD-80; WITH FULLY OPERATIONAL TCASII AND NAVAIDS; WAS IMC ON A JET AIRWAY APCHING MILTON VOR FROM THE W AT ABOUT XA40 LCL TIME ON JUL/XX/94. WE OBSERVED A LINE OF CELLS ON OUR RADAR AHEAD OF US. IT APPEARED THAT A LARGE CELL WAS SITTING DIRECTLY OVER MILTON VOR; WHICH WAS ALONG OUR AIRWAY ON OUR TRIP FROM ORD TO LGA. THERE APPEARED TO BE A BETTER CHANCE TO GO L (N) AROUND THE CELL AT MILTON; SO WE REQUESTED AND RECEIVED APPROVAL FROM CTR TO DO SO AT OUR CURRENT ALT FL290. SHORTLY AFTER; WE BROKE OUT OF THE CLOUDS AND VISUALLY OBSERVED THE LINE OF CELLS IN FRONT OF US. IT NOW WAS OBVIOUS THAT THE BUILDINGS WERE CONTINUOUS TO THE L OF MILTON (N); BUT THERE WAS A LARGE GAP TO THE R OF MILTON (S). WE REQUESTED FROM CTR A TURN S OF MILTON THROUGH THE GAP AND TOLD CTR IT WOULD BE APPROX A 170 DEG HDG. CTR APPROVED THE SOUTHERLY DEV. AS WE STARTED INTO OUR TURN TO 170 DEG WE CAME VERY CLOSE TO THE CELL; WHICH WAS NOW ON OUR L. WE TRIED TO REQUEST A TURN TO 210 DEG TO GO THROUGH THE GAP; BUT WE WERE STEPPED ON BY AN ACR Y ACFT WHICH WAS IN THE AREA. AS WE TURNED TO 210 DEGS TO AVOID CELL PENETRATION; THE CTLR FINALLY SAID 'ROGER' TO THE REQUEST TO TURN TO 210 DEGS (HE SAID NOTHING ELSE). THE SAME ACR Y ACFT THEN BEGAN TALKING FOR WHAT SEEMED LIKE 30 SECONDS ON THE RADIO ABOUT HIS PLANS TO GO THROUGH THE SAME GAP; BUT FROM THE OTHER DIRECTION. AT NO TIME DID WE KNOW HIS ALT OR LOCATION UNTIL WE RECEIVED A TA ON THE TCASII AT 12 O'CLOCK; SAME ALT. AT THIS POINT; THE CTLR TRIED TO ALERT ACR Y THAT WE WERE ON A COLLISION COURSE; BUT THE ACR Y PLT WAS STILL TALKING. THE TA QUICKLY BECAME AN RA; AND WE HEARD OUR TCASII SAY 'DSND; DSND.' WE IMMEDIATELY DSNDED FROM FL290 TO ABOUT FL280. THE CTLR FINALLY GOT IN ON THE RADIO AND TOLD ACR Y TO DSND ALSO; AND ACR Y SAID 'ROGER.' AS ACR Y PASSED ABOUT 300 FT OVER OUR HEAD AND JUST TO THE R OF US; THE CTLR TOLD US TO TURN L TO 090 (INTO THE CELL). WE TOLD CTR 'NEGATIVE' DUE TO SAFETY AND TOLD HIM WE HAD THE TFC IN SIGHT AND HE HAD JUST PASSED US. ALSO; THERE WAS ANOTHER AIRPLANE AT FL270 OR FL280 GOING W THROUGH THE GAP 10 MI IN FRONT. WE DID RPT OUR ALTDEV TO THE CTLR. WHY ACR Y ACCEPTED A DSCNT WHEN HIS TCASII MUST HAVE BEEN TELLING HIM TO CLB IS A MYSTERY.