MD80 FLC HAS TCASII RA BUT EQUIP DIFFICULT TO UNDERSTAND. EVASIVE ACTION TAKEN.

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DURING DEP WHILE FLYING THE NEWARK 5 SID WE WERE CLBING AT 330 KIAS ON A WESTERLY HDG TO INTERCEPT THE SAX VOR 252 DEG RADIAL. ZNY ADVISED OF AN EBOUND SAAB 340 VFR AT 15000 FT (NOT 15500 FT). OUR TCASII ALERTED US WITH AN RA. THE VISUAL PRESENTATION WAS A LITTLE BLURRY AND COULD NOT DECIPHER WHETHER CONFLICT WAS CLBING OR DSNDING. ALSO AUDIO WAS WEAK AND SOMEWHAT DIFFICULT TO UNDERSTAND. WHILE CLBING THROUGH 14000 FT AT APPROX 4000 FPM; ATC ADVISED US TO 'JUST GO AHEAD AND LEVEL OFF AT 15000 FT' TO AVOID A CONFLICT AND TCASII APPEARED TO BE CALLING FOR A DSCNT OF GREATER THAN 3000 FPM. AT THIS POINT WE ACQUIRED THE TFC VISUALLY AND DSNDED FROM 15300 FT TO 15000 FT AT THE SAME TIME TURNING L WITH A 30 DEG BANK TO AVOID THE CONFLICT. IRONICALLY; IT APPEARED THE CONFLICT TFC WAS ALSO AT 15000 FT AND NEVER APPEARED TO BE AVOIDING US. OUR FORTUNE WAS IN BEING ABLE TO SEE AND AVOID THE TFC AS ATC WAS VAGUE AND TCASII WAS DIFFICULT TO INTERPRET. TCASII WAS RPTED TO MAINT AS SUCH. SUPPLEMENTAL INFO FROM ACN 340213: THE SAAB 340 WAS VFR IN THE NE CORRIDOR AND THE CTLR WAS NOT REQUIRED TO PROVIDE SEPARATION; JUST A TFC CALL; BUT IT CAME LATE AND EVASION WAS REQUIRED. SUGGEST NO ONE WITH A FLT NUMBER (SCHEDULED ACR; ETC) BE ALLOWED VFR IN NE CORRIDOR.