ZNY CTLR EXPERIENCED LOSS OF SEPARATION DURING HOLDING FOR PHL.

Narrative

WHILE WORKING R26; I WAS HOLDING 8000 FT THROUGH 14000 FT AT BUNTS; INBOUND FOR PHL. 8000 FT THROUGH 12000 FT WAS COORD WITH PHL AND WERE ON PHL FREQ. ACR X WAS HOLDING AT 13000 FT ON MY FREQ. PHL CALLED AND SAID ACR Y; WHO WAS HOLDING AT 12000 FT; WAS OUT OF THE PATTERN AND THAT 8000 FT WAS AVAILABLE. I OBSERVED A TARGET IN THE PATTERN AT 10000 FT AND ASKED PHL WHO THAT WAS. PHL RESPONDED IT WAS ACR Z AND I WAS WORKING HIM. I SAID I WAS NOT AND THEN PHL SAID ACR Z WAS ON HIS FREQ AND DSNDING; WHICH I TOLD HIM I WOULD DSND ACR X REF HIM. UNFORTUNATELY; ACR W WAS RIGHT UNDER ACR X AT 11000 FT THAT I COULD NOT SEE BECAUSE OF LIMITED DATA BLOCK OVERLAP. PHL DID NOT ADVISE ME THAT THIS ACFT WAS STILL IN THE PATTERN AND WHEN I DSNDED ACR X TO 9000 FT REF ACR Z; ACR X THEN INFORMED ME OF A TCASII RESOLUTION AND CLBED TO 11500 FT. SUPPLEMENTAL INFO FROM ACN 606273: ZNY DSNDED AN ACFT ON TOP OF ONE I WAS HOLDING AT 11000 FT. HE MUST HAVE MISUNDERSTOOD WHO WAS STILL HOLDING IN THE PATTERN. THE PLT QUESTIONED WHO WAS DSNDING ABOVE HIM AND I ISSUED A DSCNT TO MY PLT AND TOLD HIM I WOULD FIND OUT THE SIT. THE PROB CAN BE CORRECTED BY HAVING ZNY STOP TERMINATING RADAR SVC OF ACFT IN A HOLDING PATTERN. THEY SHOULD CONTINUE MONITORING ACFT IN RADAR CONTACT.