Narrative:

Air carrier X was a ferry flight from europe to philadelphia. Maintaining FL390 along na route 102. In boston center airspace received first descent clearance in preparation for arrival phase down to FL310. At approximately 140 NM east of sardi intersection we were cleared to FL280 to be at FL280 60 NM east of sardi. At approximately 105 NM east of sardi we were told to descend to FL280 now. Somewhere in here we were given a vector heading of 280 degree. As we descended through FL285 boston center told us to 'maintain FL290'. I replied, 'too late, we are at FL283'. I immediately broke the descent and started a climb back to FL290. The controller advised us we had converging traffic at 3 O'clock, FL280 and gave us another heading further left (240 degree, I believe). At this point we observed air carrier Y aircraft at our 2 O'clock position, about 1000 ft below, banking right. A few moments later the controller questioned me regarding our clearance to FL280 and inferred the error was ours. At this point it seemed there was some sort of discussion in the backgnd at boston center. The following instructions became quite 'concise'. It seemed the controller was being doubly careful all ATC instructions were being understood.

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Original NASA ASRS Text

Title: ACR X DSCNT TO OCCUPIED ALT HAD LTSS WITH ACR Y. SYSTEM ERROR.

Narrative: ACR X WAS A FERRY FLT FROM EUROPE TO PHILADELPHIA. MAINTAINING FL390 ALONG NA RTE 102. IN BOSTON CENTER AIRSPACE RECEIVED FIRST DSCNT CLRNC IN PREPARATION FOR ARR PHASE DOWN TO FL310. AT APPROX 140 NM E OF SARDI INTXN WE WERE CLRED TO FL280 TO BE AT FL280 60 NM E OF SARDI. AT APPROX 105 NM E OF SARDI WE WERE TOLD TO DSND TO FL280 NOW. SOMEWHERE IN HERE WE WERE GIVEN A VECTOR HDG OF 280 DEG. AS WE DSNDED THROUGH FL285 BOSTON CENTER TOLD US TO 'MAINTAIN FL290'. I REPLIED, 'TOO LATE, WE ARE AT FL283'. I IMMEDIATELY BROKE THE DSCNT AND STARTED A CLB BACK TO FL290. THE CTLR ADVISED US WE HAD CONVERGING TFC AT 3 O'CLOCK, FL280 AND GAVE US ANOTHER HDG FURTHER L (240 DEG, I BELIEVE). AT THIS POINT WE OBSERVED ACR Y ACFT AT OUR 2 O'CLOCK POS, ABOUT 1000 FT BELOW, BANKING R. A FEW MOMENTS LATER THE CTLR QUESTIONED ME REGARDING OUR CLRNC TO FL280 AND INFERRED THE ERROR WAS OURS. AT THIS POINT IT SEEMED THERE WAS SOME SORT OF DISCUSSION IN THE BACKGND AT BOSTON CENTER. THE FOLLOWING INSTRUCTIONS BECAME QUITE 'CONCISE'. IT SEEMED THE CTLR WAS BEING DOUBLY CAREFUL ALL ATC INSTRUCTIONS WERE BEING UNDERSTOOD.

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.