Narrative:

As we approached the duty runway 18R (#2 in line), the copilot switched to tower frequency. The aircraft ahead was cleared into position, then cleared for takeoff. Tower then broadcast 'air carrier xx position and hold.' due to the similarity of call sign (we were air carrier xy) I assumed that the tower controller had simply misspoken our call sign, so I proceeded into position on the runway as the copilot responded, 'that's air carrier xy position and hold.' although the tower's response was prompt, by the time he said, 'oh, if that's air carrier xy, hold short, we need a release from ord (our destination), I had proceeded 20' past the hold short line. At this point the tower operator had an aircraft on final and us on the runway west/O a release, so he cleared us for takeoff. I should have cleared up the call sign confusion before acting.

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Original NASA ASRS Text

Title: CALL SIGN CONFUSION RESULTED IN ACR LGT TAXIING INTO POSITION FOR TKOF WITHOUT CLRNC.

Narrative: AS WE APCHED THE DUTY RWY 18R (#2 IN LINE), THE COPLT SWITCHED TO TWR FREQ. THE ACFT AHEAD WAS CLRED INTO POS, THEN CLRED FOR TKOF. TWR THEN BROADCAST 'ACR XX POS AND HOLD.' DUE TO THE SIMILARITY OF CALL SIGN (WE WERE ACR XY) I ASSUMED THAT THE TWR CTLR HAD SIMPLY MISSPOKEN OUR CALL SIGN, SO I PROCEEDED INTO POS ON THE RWY AS THE COPLT RESPONDED, 'THAT'S ACR XY POS AND HOLD.' ALTHOUGH THE TWR'S RESPONSE WAS PROMPT, BY THE TIME HE SAID, 'OH, IF THAT'S ACR XY, HOLD SHORT, WE NEED A RELEASE FROM ORD (OUR DEST), I HAD PROCEEDED 20' PAST THE HOLD SHORT LINE. AT THIS POINT THE TWR OPERATOR HAD AN ACFT ON FINAL AND US ON THE RWY W/O A RELEASE, SO HE CLRED US FOR TKOF. I SHOULD HAVE CLRED UP THE CALL SIGN CONFUSION BEFORE ACTING.

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.