Narrative:

En route to lga we began our descent out of FL290 to FL240. This clearance was superseded by a clearance to cross marcc (milton 5 arrival to lga) at FL180. Prior to reaching FL180 the ZNY controller again revised the clearance limit to 5 west of abe at what was thought to be 10000', but later turned out to be 13000'. 10000' however was what I read back and subsequently not challenged nor corrected by the issuing controller. During this time frame my attention as the PNF was diverted to getting the ATIS and gate information as well as saying goodbye to the passenger with ETA prior to sterile cockpit conditions. As I performed these essential duties I delegated the radio communication to the copilot who was flying. As I again assumed the communication duties the controller challenge our present altitude to which I responded passing 11000' plus (approximately) for 10000'. Obviously concerned he responded with the fact that our clearance limit was 13000', and that we had been issued 12 O'clock traffic at 12000'. Obviously startled by the situation I turned to the copilot for confirmation, who also believed our limit to be 10000' and that he had responded to the traffic with a stated 'in IMC conditions.' once on the ground I contacted the center by phone and spoke to the controller and supervisor who informed me that upon review the tapes, although 13000' was my issued clearance limit, 10000' was clearly my readback and that the controller had not caught it. A potentially dangerous situation occurred and although the controller did err, workload in our cockpit and distraction in handling additional duties that in a 3-M cockpit would be handled by the F/east was an obvious contributing factor limiting my ability to recognize some key 'red flags' (warnings) which might have alerted us to this potentially dangerous situation that was unfolding. Callback conversation with the reporter revealed the following: clarified types of aircraft. Reporter not aware of air carrier Y direction of flight. Has heard through company that FAA eastern region is investigating incident. Thinks now that he should have questioned descent to 10000' as chart shows expect altitude of 13000'. Also agrees that first officer should have questioned descent to 10000' when controller gave traffic at 12000'. ZNY supervisor gave him miss distances during phone review of incident.

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Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR.

Narrative: ENRTE TO LGA WE BEGAN OUR DSCNT OUT OF FL290 TO FL240. THIS CLRNC WAS SUPERSEDED BY A CLRNC TO CROSS MARCC (MILTON 5 ARR TO LGA) AT FL180. PRIOR TO REACHING FL180 THE ZNY CTLR AGAIN REVISED THE CLRNC LIMIT TO 5 W OF ABE AT WHAT WAS THOUGHT TO BE 10000', BUT LATER TURNED OUT TO BE 13000'. 10000' HOWEVER WAS WHAT I READ BACK AND SUBSEQUENTLY NOT CHALLENGED NOR CORRECTED BY THE ISSUING CTLR. DURING THIS TIME FRAME MY ATTN AS THE PNF WAS DIVERTED TO GETTING THE ATIS AND GATE INFO AS WELL AS SAYING GOODBYE TO THE PAX WITH ETA PRIOR TO STERILE COCKPIT CONDITIONS. AS I PERFORMED THESE ESSENTIAL DUTIES I DELEGATED THE RADIO COM TO THE COPLT WHO WAS FLYING. AS I AGAIN ASSUMED THE COM DUTIES THE CTLR CHALLENGE OUR PRESENT ALT TO WHICH I RESPONDED PASSING 11000' PLUS (APPROX) FOR 10000'. OBVIOUSLY CONCERNED HE RESPONDED WITH THE FACT THAT OUR CLRNC LIMIT WAS 13000', AND THAT WE HAD BEEN ISSUED 12 O'CLOCK TFC AT 12000'. OBVIOUSLY STARTLED BY THE SITUATION I TURNED TO THE COPLT FOR CONFIRMATION, WHO ALSO BELIEVED OUR LIMIT TO BE 10000' AND THAT HE HAD RESPONDED TO THE TFC WITH A STATED 'IN IMC CONDITIONS.' ONCE ON THE GND I CONTACTED THE CENTER BY PHONE AND SPOKE TO THE CTLR AND SUPVR WHO INFORMED ME THAT UPON REVIEW THE TAPES, ALTHOUGH 13000' WAS MY ISSUED CLRNC LIMIT, 10000' WAS CLEARLY MY READBACK AND THAT THE CTLR HAD NOT CAUGHT IT. A POTENTIALLY DANGEROUS SITUATION OCCURRED AND ALTHOUGH THE CTLR DID ERR, WORKLOAD IN OUR COCKPIT AND DISTR IN HANDLING ADDITIONAL DUTIES THAT IN A 3-M COCKPIT WOULD BE HANDLED BY THE F/E WAS AN OBVIOUS CONTRIBUTING FACTOR LIMITING MY ABILITY TO RECOGNIZE SOME KEY 'RED FLAGS' (WARNINGS) WHICH MIGHT HAVE ALERTED US TO THIS POTENTIALLY DANGEROUS SITUATION THAT WAS UNFOLDING. CALLBACK CONVERSATION WITH THE RPTR REVEALED THE FOLLOWING: CLARIFIED TYPES OF ACFT. RPTR NOT AWARE OF ACR Y DIRECTION OF FLT. HAS HEARD THROUGH COMPANY THAT FAA EASTERN REGION IS INVESTIGATING INCIDENT. THINKS NOW THAT HE SHOULD HAVE QUESTIONED DSCNT TO 10000' AS CHART SHOWS EXPECT ALT OF 13000'. ALSO AGREES THAT F/O SHOULD HAVE QUESTIONED DSCNT TO 10000' WHEN CTLR GAVE TFC AT 12000'. ZNY SUPVR GAVE HIM MISS DISTANCES DURING PHONE REVIEW OF INCIDENT.

Data retrieved from NASA's ASRS site as of August 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.