Narrative:

Assigned to wrong way FL410 by ATC for traffic. Cleared to descend to FL390. I read back the clearance. At approximately FL403 ATC inquired our altitude and I replied descending to FL390. He said that was for another aircraft and to expedite back to FL410. Captain began climbing our aircraft and I read back the climb clearance and also stated that I had read back the descent clearance. 2 aircraft at FL390, one eastbound several mi to our left, one wbound approximately 8-9 NM to our right, separation never less than 1000- 1200 ft. No TCASII TA or RA, although target to south had just gone to cautionary (yellow). Supplemental information from acn 393833: descending through FL402 I noticed TCASII had yellow symbol near aircraft, so stopped descent as first officer saw aircraft. Later I was informed that the clearance was for our air carrier xy and was read back by that aircraft on another frequency. They also had our readback sort of -- it was garbled with another transmission. Since both pilots thought the call was for them (us) then the readback being the backup also did not work because of the controller having to transmit and receive multiple frequency and did not think anything of the garbled call. I believed we were the only air carrier X on our frequency and this may have contributed to our believing he was talking to us.

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Original NASA ASRS Text

Title: AN ACR LGT FLC TAKES A CLRNC MEANT FOR ANOTHER COMPANY ACFT AND STARTS DSCNT AFTER READBACK OF CLRNC. TCASII AND CTLR CATCH THE ERROR. RPTR STATES THAT THE CTLR WAS WORKING TWO SEPARATE FREQS AND MISSED HIS READBACK.

Narrative: ASSIGNED TO WRONG WAY FL410 BY ATC FOR TFC. CLRED TO DSND TO FL390. I READ BACK THE CLRNC. AT APPROX FL403 ATC INQUIRED OUR ALT AND I REPLIED DSNDING TO FL390. HE SAID THAT WAS FOR ANOTHER ACFT AND TO EXPEDITE BACK TO FL410. CAPT BEGAN CLBING OUR ACFT AND I READ BACK THE CLB CLRNC AND ALSO STATED THAT I HAD READ BACK THE DSCNT CLRNC. 2 ACFT AT FL390, ONE EBOUND SEVERAL MI TO OUR L, ONE WBOUND APPROX 8-9 NM TO OUR R, SEPARATION NEVER LESS THAN 1000- 1200 FT. NO TCASII TA OR RA, ALTHOUGH TARGET TO S HAD JUST GONE TO CAUTIONARY (YELLOW). SUPPLEMENTAL INFO FROM ACN 393833: DSNDING THROUGH FL402 I NOTICED TCASII HAD YELLOW SYMBOL NEAR ACFT, SO STOPPED DSCNT AS FO SAW ACFT. LATER I WAS INFORMED THAT THE CLRNC WAS FOR OUR ACR XY AND WAS READ BACK BY THAT ACFT ON ANOTHER FREQ. THEY ALSO HAD OUR READBACK SORT OF -- IT WAS GARBLED WITH ANOTHER XMISSION. SINCE BOTH PLTS THOUGHT THE CALL WAS FOR THEM (US) THEN THE READBACK BEING THE BACKUP ALSO DID NOT WORK BECAUSE OF THE CTLR HAVING TO XMIT AND RECEIVE MULTIPLE FREQ AND DID NOT THINK ANYTHING OF THE GARBLED CALL. I BELIEVED WE WERE THE ONLY ACR X ON OUR FREQ AND THIS MAY HAVE CONTRIBUTED TO OUR BELIEVING HE WAS TALKING TO US.

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.