Narrative:

En route from montreal, canada, to wilmington, oh, charter X checked in with ZBW and they cleared us to FL350. They then amended the climb to FL260. Climbing through FL245, both my first officer and I heard, 'charter X cleared to FL350.' the first officer read back 'charter X cleared to FL350.' nothing further was heard. Climbing through FL285, ZBW asked for our altitude. The first officer replied and we heard ZBW advise some other aircraft that 'the traffic is above you now.' ZBW then asked us if we remembered our climb being amended to FL260. The first officer replied 'yes, but then we were reclred to FL350.' ZBW then told us that that call was for company charter Y. We had not heard company on frequency. Both of us heard FL350 for charter X and charter X definitely read back FL350. During this discussion, we observed traffic pass to our right, approximately 150 degree heading difference, approximately 2000 ft below our altitude. I assume that aircraft likely had a TCASII indication and that 10 NM separation may have been broken. After our original FL260 restr, ZBW reported our traffic as northbound (our heading was 235 degrees) at our 9 O'clock. If that was the position of our traffic, when we heard our clearance to FL350, it made sense as that traffic would have been behind us at that point. This incident may have been avoided if ZBW had advised us that company charter flight was on frequency and more importantly it would have been avoided if they had reacted to our readback of FL350. The resulting loss of separation did not result in a conflict, but the potential was there.

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Original NASA ASRS Text

Title: FLC OF AN LTT CARGO JET RESPONDED TO ANOTHER SIMILAR SOUNDING CALL SIGN AND CLBED FROM ASSIGNED ALT.

Narrative: ENRTE FROM MONTREAL, CANADA, TO WILMINGTON, OH, CHARTER X CHKED IN WITH ZBW AND THEY CLRED US TO FL350. THEY THEN AMENDED THE CLB TO FL260. CLBING THROUGH FL245, BOTH MY FO AND I HEARD, 'CHARTER X CLRED TO FL350.' THE FO READ BACK 'CHARTER X CLRED TO FL350.' NOTHING FURTHER WAS HEARD. CLBING THROUGH FL285, ZBW ASKED FOR OUR ALT. THE FO REPLIED AND WE HEARD ZBW ADVISE SOME OTHER ACFT THAT 'THE TFC IS ABOVE YOU NOW.' ZBW THEN ASKED US IF WE REMEMBERED OUR CLB BEING AMENDED TO FL260. THE FO REPLIED 'YES, BUT THEN WE WERE RECLRED TO FL350.' ZBW THEN TOLD US THAT THAT CALL WAS FOR COMPANY CHARTER Y. WE HAD NOT HEARD COMPANY ON FREQ. BOTH OF US HEARD FL350 FOR CHARTER X AND CHARTER X DEFINITELY READ BACK FL350. DURING THIS DISCUSSION, WE OBSERVED TFC PASS TO OUR R, APPROX 150 DEG HDG DIFFERENCE, APPROX 2000 FT BELOW OUR ALT. I ASSUME THAT ACFT LIKELY HAD A TCASII INDICATION AND THAT 10 NM SEPARATION MAY HAVE BEEN BROKEN. AFTER OUR ORIGINAL FL260 RESTR, ZBW RPTED OUR TFC AS NBOUND (OUR HDG WAS 235 DEGS) AT OUR 9 O'CLOCK. IF THAT WAS THE POS OF OUR TFC, WHEN WE HEARD OUR CLRNC TO FL350, IT MADE SENSE AS THAT TFC WOULD HAVE BEEN BEHIND US AT THAT POINT. THIS INCIDENT MAY HAVE BEEN AVOIDED IF ZBW HAD ADVISED US THAT COMPANY CHARTER FLT WAS ON FREQ AND MORE IMPORTANTLY IT WOULD HAVE BEEN AVOIDED IF THEY HAD REACTED TO OUR READBACK OF FL350. THE RESULTING LOSS OF SEPARATION DID NOT RESULT IN A CONFLICT, BUT THE POTENTIAL WAS THERE.

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.