ALTDEV ALT EXCURSION DUE TO TCASII RA.

Narrative

WE HAD JUST SWITCHED FROM PHL TRACON TO ZNY; LEVEL 10000 FT. CTR CALLED OUT VFR TFC AT 10500 FT; 1 O'CLOCK; AND 5 MI. TCASII WAS ON THE 10 MI SCALE. THERE WERE 2 TARGETS ON THE TCASII BOTH AT 1 O'CLOCK; THE FIRST 500 FT ABOVE US AND 5 MI; THE SECOND 1000 FT ABOVE US AND 8 MI. I THOUGHT I HAD A VISUAL ON THE VFR; 10500 FT TFC. I WAS WRONG. I HAD VISUAL ON THE TFC 1000 FT ABOVE US. THE WX WAS CLR AND EXCELLENT VISIBILITY. I BELIEVE IT WAS LESS THAN 2 MINS AFTER CTR CALLED OUT THE 10500 FT TFC WE GOT A TCASII RA TO DSND. CAPT IMMEDIATELY FOLLOWED RA. I ADVISED CTR WE WERE DSNDING WITH AN RA AND ASKED FOR VECTORS AWAY FROM TFC. AT 9600 FT RA STOPPED AND ADVISED CLR OF CONFLICT AND WE RETURNED TO 10000 FT. I WAS SURPRISED I NEVER SAW THE TFC. CTR DID NOT CALL OUT THE OTHER 1 O'CLOCK TFC 1000 FT ABOVE US. THAT WAS THE FIRST TARGET I SAW; MADE THE MISTAKE OF THINKING I HAD THE CLOSER 10500 FT TFC AND FIXATED ON IT. WHEN WE GOT THE RA I AGAIN FIXATED ON THE IVSI TO MAKE SURE THE CAPT WAS FOLLOWING THE RA. I DID NOTICE DURING THE RA THE TFC ON TCASII PASSING; I BELIEVE; 600 FT ABOVE AND ESTIMATE A 1/4 MI FROM US. THE CAPT SAID HE SAW THE TFC COME FROM THE CTR WINDSHIELD POST GOING R TO L. HE THOUGHT THE TFC WAS MUCH CLOSER AND 300 FT ABOVE US. IT WAS MY FIRST RA AND TCASII DID A GOOD JOB; GLAD IT IS REQUIRED EQUIP AND ABOARD! I CANNOT BELIEVE THE FAA DOES NOT REQUIRE TCASII ON ALL COMMUTER/REGIONAL AIRLINE EQUIP.