AN ACR PILOT ON IMC VECTORS FOR JFK RPTS ALTERING HDG AFTER A VFR ACFT IN IMC GENERATED A TCAS TA WHILE CLAIMING AN IMPOSSIBLE VISUAL SEPARATION.

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WE WERE ON VECTORS FOR THE ILS RWY 22L APCH INTO JFK. THE WX AT THE FIELD WAS IFR WITH RAIN AND FOG. WE WERE IN IMC CONDITIONS WITH RAIN SHOWERS AND HAD BEEN SINCE OUR DSCNT FROM CRUISE ALT OF FL310. NEW YORK APCH WAS HANDLING US. WE WERE HDG 180 DEGS AND IN A DSCNT FROM 13000 FT TO 4000 FT. WE WERE VERY FAMILIAR WITH THE SEQUENCE OF CTLR VECTORS AND ALTS FOR RWY 22L. THE DSCNT FROM 13000 FT TO 4000 FT WAS A LARGE ALT CHANGE. WE ARE ACCUSTOMED TO A CLRNC FROM 13000 FT TO 8000 FT INITIALLY BUT WE DIDN'T QUESTION IT. THEN WE WERE ISSUED A HDG CHANGE TO 040 DEGS. NOW THIS DID SEEM ODD SINCE WE USUALLY RECEIVE ABOUT A 130 DEG OR SO HDG PRIOR TO THE 040 DEG HDG. THIS PROMPTED THE FO AND I TO COMMENT THAT THIS WAS A STRANGE HDG. AS I ASKED THE CTLR TO VERIFY THE HDG FOR ACR X AS 040 DEGS; THE FO STOPPED THE ACFT TURN UNTIL CONFIRMATION WAS RECEIVED AS HE FELT THAT TO BE AN ODD HDG FOR OUR LOCATION ALSO. THE CTLR VERIFIED THE HDG AS 040 DEGS AND FO RESTARTED THE TURN. SHORTLY AFTER HIS XMISSION ATC THEN STATED; ACR X LEVELOFF AT WHATEVER ALT YOU ARE AT NOW. I MESSED UP. (OR WORDS VERY SIMILAR) I REPLIED THAT WE WERE LEVEL AT 6000 FT AND I THINK I ASKED IF HE WANTED US TO CLB BACK UP. I THINK HE SAID NO THIS WAS OK. IN THE INTERIM THE FO HAD DISCONNECTED THE AUTOPLT TO HAND FLY TO RESPOND RAPIDLY TO HIS COMMAND TO LEVEL OFF AT 6000 FT AS WE WERE PROBABLY AT 5800 FT OR SO WHEN HE CLBED BACK UP. THIS WAS VERY UNNERVING TO BOTH OF US GIVEN THE FACT THAT WE WERE IMC AND AT AN ALT THAT WAS NOT USUALLY ASSIGNED. WE WERE CONVINCED THAT WE SHOULD HAVE BEEN ON A SE HDG THAT WOULD HAVE PUT US S OF OUR PRESENT POS. IN THE NEXT FEW XMISSIONS TO ATC I MADE A POINT TO ADVISE WE WERE AT 6000 FT TO EMPHASIZE TO THE CTLR WE WERE NOT AT HIS ORIGINALLY CLRED ALT OF 4000 FT. I FELT THIS WAS NECESSARY TO DRAW HIS ATTN TO OUR GEOGRAPHICAL POS AND ALT. WE THEN NOTICED THAT WE HAD TFC AHEAD OF US JUST OUTSIDE OF 5 MI CO-ALT OF 6000 FT. AGAIN; THIS SEEMED VERY ODD TO BE FOLLOWING AN ACFT THAT WAS ALSO AT AN 'OFF ALT.' WE WATCHED THE TCAS AS HE BECAME A SOLID WHITE INTRUDER AND IT THEN APPEARED THAT THE TFC WAS COMING TOWARDS US. I TOLD THE FO TO PREPARE FOR A TURN TO THE E AND ASKED ATC ABOUT THIS TFC. THE ACFT WAS NOW APCHING AT 4 MI AND THE TCAS GAVE US A YELLOW TFC TA WARNING. I ADVISED ATC OF THE WARNING AND WAS TOLD THE ACFT WAS AT 6000 FT VFR AND WAS MAINTAINING SEPARATION OR WORDS TO THAT EFFECT. THERE WAS NO WAY THIS TFC COULD SEE US AS WE WERE IN SOLID IMC AND RAIN. AT THIS POINT I HAD LOST CONFIDENCE IN THE CTLR'S SITUATIONAL AWARENESS. THE FACT THAT THIS CTLR HAD LEVELED US OFF AT AN ODD ALT IN A LOCATION CLOSER TO THE ARPT THAN WE NORMALLY ARE AND HIS BELIEVING THAT THIS TFC WAS VFR AND COULD SEE US FURTHER UNDERMINED MY CONFIDENCE IN HIS GRASP OF THE SITUATION. I TOLD THE FO TO TURN IMMEDIATELY TO A HDG OF 100 DEGS SINCE THE AREA WAS CLR ON TCAS. IN MY HASTE TO ADVISE ATC OF OUR INTENTIONS I MISSPOKE AND SAID WE WERE TURNING R TO 010 DEGS AS OPPOSED TO R TO 100 DEGS. ATC WAS CONFUSED BY MY MISSTATEMENT BUT DIDN'T SEEM TO FEEL THAT THE OTHER ACFT WAS A THREAT TO US. THE ACFT PASSED OFF THE L AND WE THEN CONTINUED WITH ATC INSTRUCTIONS AND LANDED WITHOUT FURTHER INCIDENT. I WAS SHAKEN BY THIS INCIDENT. I BELIEVE THAT WHEN ATC TOLD US TO LEVEL OFF IMMEDIATELY; FROM THAT POINT ON I WAS CONVINCED THAT WE WERE NOT AT THE RIGHT PLACE FOR OUR SEQUENCE. THAT LED ME TO DOUBT THE CTLR'S EXPLANATION OF THE TARGET AND TO TAKE MY OWN CORRECTIVE ACTION PRIOR TO GETTING A TCAS RA. I DID NOT DECLARE AN EMER DURING THIS RAPID SEQUENCE OF EVENTS; HOWEVER I DID ADVISE THE CTLR OF OUR HDG CHANGE FOR TFC AVOIDANCE. THE WAY THE EVENTS UNFOLDED NECESSITATED MY COM AND ACTIONS TAKING PRECEDENCE OVER VERBALLY DECLARING AN EMER.