Narrative:

I was working R19 at ZDC during a period of moderate traffic and WX deviations. Several aircraft on nanci 5 (lga) arrival needed to deviate near dqo VOR. I issued descent to 2 aircraft to 11000 ft and advised air carrier X to deviate east of course after leaving 16000 ft. After unkeying microphone, there was some garble on frequency and then air carrier X completed readback of altitude clearance. Several seconds later I observed air carrier Y descend below FL240 and cross with traffic below at FL230. I asked Y to verify assigned altitude as FL240 and crew responded I had given descent to 11000 ft. I was not aware that Y was on my frequency and attributed garbled noise to Y checking on at FL240. The aircraft missed by 4 plus mi and were already moving away from each other, so there was no further need for action on my part. The Y crew must have thought the clearance for X was theirs. I guess I could have responded to the garble to verify no one else took clearance, but there was really no need in my mind to verify since Y was not on the frequency as far as I knew. Review of tapes showed Y was on when I assumed position. My failure to recognize a potential conflict with aircraft accepting a clearance and the crew's part of not listening to call signs led to this occurrence. Supplemental information from acn 312940: first officer flying the warrd 4 arrival to ewr at FL240 at ridgy. Received clearance to descend to 11000 ft by ZDC. Approach has an expect clearance to cross holey at 11000 ft. Started descent upon receiving clearance. At about FL220, ZDC requested our clearance limit, we told them 11000 ft. They said to stop at 16000 ft. After changing controling frequency, we were asked to contact ZDC on the ground. We could have accepted another flight's clearance and our readback was possibly covered. We had TCASII set at 40 DME and below and had no targets. On the ground ATC said we had approached another aircraft by 400 ft vertically and 4.3 mi horizontally.

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Original NASA ASRS Text

Title: ACR Y TOOK ACR X CLRNC, HAD LTSS WITH ANOTHER ACFT.

Narrative: I WAS WORKING R19 AT ZDC DURING A PERIOD OF MODERATE TFC AND WX DEVS. SEVERAL ACFT ON NANCI 5 (LGA) ARR NEEDED TO DEVIATE NEAR DQO VOR. I ISSUED DSCNT TO 2 ACFT TO 11000 FT AND ADVISED ACR X TO DEVIATE E OF COURSE AFTER LEAVING 16000 FT. AFTER UNKEYING MIKE, THERE WAS SOME GARBLE ON FREQ AND THEN ACR X COMPLETED READBACK OF ALT CLRNC. SEVERAL SECONDS LATER I OBSERVED ACR Y DSND BELOW FL240 AND CROSS WITH TFC BELOW AT FL230. I ASKED Y TO VERIFY ASSIGNED ALT AS FL240 AND CREW RESPONDED I HAD GIVEN DSCNT TO 11000 FT. I WAS NOT AWARE THAT Y WAS ON MY FREQ AND ATTRIBUTED GARBLED NOISE TO Y CHKING ON AT FL240. THE ACFT MISSED BY 4 PLUS MI AND WERE ALREADY MOVING AWAY FROM EACH OTHER, SO THERE WAS NO FURTHER NEED FOR ACTION ON MY PART. THE Y CREW MUST HAVE THOUGHT THE CLRNC FOR X WAS THEIRS. I GUESS I COULD HAVE RESPONDED TO THE GARBLE TO VERIFY NO ONE ELSE TOOK CLRNC, BUT THERE WAS REALLY NO NEED IN MY MIND TO VERIFY SINCE Y WAS NOT ON THE FREQ AS FAR AS I KNEW. REVIEW OF TAPES SHOWED Y WAS ON WHEN I ASSUMED POS. MY FAILURE TO RECOGNIZE A POTENTIAL CONFLICT WITH ACFT ACCEPTING A CLRNC AND THE CREW'S PART OF NOT LISTENING TO CALL SIGNS LED TO THIS OCCURRENCE. SUPPLEMENTAL INFO FROM ACN 312940: FO FLYING THE WARRD 4 ARR TO EWR AT FL240 AT RIDGY. RECEIVED CLRNC TO DSND TO 11000 FT BY ZDC. APCH HAS AN EXPECT CLRNC TO CROSS HOLEY AT 11000 FT. STARTED DSCNT UPON RECEIVING CLRNC. AT ABOUT FL220, ZDC REQUESTED OUR CLRNC LIMIT, WE TOLD THEM 11000 FT. THEY SAID TO STOP AT 16000 FT. AFTER CHANGING CTLING FREQ, WE WERE ASKED TO CONTACT ZDC ON THE GND. WE COULD HAVE ACCEPTED ANOTHER FLT'S CLRNC AND OUR READBACK WAS POSSIBLY COVERED. WE HAD TCASII SET AT 40 DME AND BELOW AND HAD NO TARGETS. ON THE GND ATC SAID WE HAD APCHED ANOTHER ACFT BY 400 FT VERTLY AND 4.3 MI HORIZLY.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.