Narrative:

While descending into the phl area, at 25000', we were given a clearance to cross the lrp VOR at 11000'. At 15000' we were given a 15 degree turn to the left and told to maintain 13000' for traffic. 3 mins later we were given (or so we thought!) a clearance to 10000'. We read it back to the controller and started to descend. At 12500' our altitude was questioned by the controller, and we immediately returned to 13000'. The aircraft we were in conflict with was a light twin at 12000', directly ahead 3-4 mi in the opp direction, whose call sign was xyz bca. There was an awful lot of talk on the frequency. I assume the controller had his hands full--so much so, perhaps, the readback by air carrier bca just didn't trigger his mind. After having our descent delayed, we heard what we wanted to hear. We had heard no previous communication between ATC and xyz bca. This problem of identical flight #'south on the same frequency is not new. Now that we have radar and computers, couldn't we assign one of the aircraft a temporary call sign while it's operating in the sector? I.e., air carrier X/red, air carrier Y/blue, air carrier Z/white, etc. Perhaps even something as simple as the registration # of the aircraft for 'ATC' purposes. There's only 'one' each of them in the world!!

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Original NASA ASRS Text

Title: ALT DEVIATION EXCURSION FROM CLRNC ALT CAUSES POSSIBLE LESS THAN STANDARD SEPARATION WITH OPPOSITE DIRECTION TRAFFIC.

Narrative: WHILE DSNDING INTO THE PHL AREA, AT 25000', WE WERE GIVEN A CLRNC TO CROSS THE LRP VOR AT 11000'. AT 15000' WE WERE GIVEN A 15 DEG TURN TO THE LEFT AND TOLD TO MAINTAIN 13000' FOR TFC. 3 MINS LATER WE WERE GIVEN (OR SO WE THOUGHT!) A CLRNC TO 10000'. WE READ IT BACK TO THE CTLR AND STARTED TO DSND. AT 12500' OUR ALT WAS QUESTIONED BY THE CTLR, AND WE IMMEDIATELY RETURNED TO 13000'. THE ACFT WE WERE IN CONFLICT WITH WAS A LIGHT TWIN AT 12000', DIRECTLY AHEAD 3-4 MI IN THE OPP DIRECTION, WHOSE CALL SIGN WAS XYZ BCA. THERE WAS AN AWFUL LOT OF TALK ON THE FREQ. I ASSUME THE CTLR HAD HIS HANDS FULL--SO MUCH SO, PERHAPS, THE READBACK BY ACR BCA JUST DIDN'T TRIGGER HIS MIND. AFTER HAVING OUR DSCNT DELAYED, WE HEARD WHAT WE WANTED TO HEAR. WE HAD HEARD NO PREVIOUS COM BTWN ATC AND XYZ BCA. THIS PROB OF IDENTICAL FLT #'S ON THE SAME FREQ IS NOT NEW. NOW THAT WE HAVE RADAR AND COMPUTERS, COULDN'T WE ASSIGN ONE OF THE ACFT A TEMPORARY CALL SIGN WHILE IT'S OPERATING IN THE SECTOR? I.E., ACR X/RED, ACR Y/BLUE, ACR Z/WHITE, ETC. PERHAPS EVEN SOMETHING AS SIMPLE AS THE REGISTRATION # OF THE ACFT FOR 'ATC' PURPOSES. THERE'S ONLY 'ONE' EACH OF THEM IN THE WORLD!!

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.