PLT OF AN SMT TWIN TOOK EVASIVE ACTION BY TURNING IN ORDER TO MAINTAIN SUFFICIENT SEPARATION. NMAC.

Narrative

WHILE WBOUND AT 12000 FT; ZNY PROVIDED A POS RPT OF AN HS125 AT MY 3 O'CLOCK AND APPROX 10 MI; DSNDING FROM 13000 FT TO 11000 FT. I PICKED UP THE HS125 VISUALLY AND RPTED SUCH TO CTR. I WAS GIVEN A 'MAINTAIN VISUAL SEPARATION' INSTRUCTION BY CTR AND HEARD CTR CLR THE JET TO 11000 FT WHILE ALSO PROVIDING A POS RPT ON MYSELF. THE JET PLT ACKNOWLEDGED THE CLRNC; BUT DID NOT RPT ME IN SIGHT. I CONTINUED TO TRACK THE JET AND AT ABOUT 4 MI SEPARATION DETERMINED THAT HIS DSCNT MIGHT TAKE HIM THROUGH MY ALT AT A VERY CLOSE RANGE. DUE TO FREQ CONGESTION; I WAS UNABLE TO COMMUNICATE THIS CONCERN WITH CTR. AS THE JET WAS CONVERGING ON ME AT A R ANGLE; IN A DSCNT; I FELT THAT NEITHER A CLB NOR DSCNT WOULD BE THE SAFEST ACTION TO TAKE AND INITIATED A SHARP; R TURN INTO THE JET. THIS WAS INITIATED IN ORDER TO MAINTAIN VISUAL CONTACT WITH THE JET AT ALL TIMES. HAVING COMPLETED A 90 DEG TURN TO THE R; THE JET PASSED SLIGHTLY ABOVE MY ALT (500 FT VERT SEPARATION; AND ABOUT 400 FT HORIZ SEPARATION) AND OFF MY L WING. THE JET APPEARED TO MAKE NO CORRECTIONS OR DEVS IN HIS DSCNT TO AVOID ME. I RETURNED TO ORIGINAL HDG; CONTACTED THE CTR AND INFORMED THEM OF MY DEV. LATER; I ASKED THE CTLR HOW CLOSE OUR SEPARATION WAS ON HIS SCREEN. HIS REPLY WAS; 'VERY CLOSE.' CONCLUSIONS: 1) SHOULD NOT HAVE ACCEPTED A VISUAL SEPARATION WITH A XING TFC WHICH WOULD DSND THROUGH MY ALT. 2) MIGHT HAVE ASKED CTLR TO HOLD THE JET AT 13000 FT UNTIL HE WAS CLOSER; OR HAD ME IN SIGHT. 3) EVEN ON AN IFR PLAN; VISUAL SEPARATION IS STILL THE PLT'S RESPONSIBILITY.