Narrative:

Thought 2 aircraft took clearance for an mlt X to 9000 ft. Ask who took it and no response. To make sure, I told large transport Y to maintain 11000, but I said 9000. Don't know why, I wanted to say 11000 to make sure large transport Y stayed at 11000. Large transport Y did not respond, but descended shortly after issuance. Planning error on my behalf.

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Original NASA ASRS Text

Title: ACR REPLY TO WRONG CALL SIGN. CTLR DIDN'T CATCH ERROR AT FIRST, THEN COULDN'T CONTACT LGT. LTSS OCCURRED.

Narrative: THOUGHT 2 ACFT TOOK CLRNC FOR AN MLT X TO 9000 FT. ASK WHO TOOK IT AND NO RESPONSE. TO MAKE SURE, I TOLD LGT Y TO MAINTAIN 11000, BUT I SAID 9000. DON'T KNOW WHY, I WANTED TO SAY 11000 TO MAKE SURE LGT Y STAYED AT 11000. LGT Y DID NOT RESPOND, BUT DSNDED SHORTLY AFTER ISSUANCE. PLANNING ERROR ON MY BEHALF.

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.