Narrative:

We were cleared onto runway 32L at intersection T10 to hold. I was expecting a takeoff clearance after the aircraft that had just landed cleared the runway. I was not aware that tower was working a flight with a similar call sign (air carrier Y XXX -- we were air carrier X yxx) on the same frequency, but a different runway. It is possible that my situational awareness was not at an all time high due to the hour, but it is also true that no special effort was made to make us aware of his presence on the frequency. At any rate, we responded to what all 4 of us (so operating experience in progress) thought was our takeoff clearance and read it back to tower. Tower made no comment and we heard no one else acknowledge the clearance. We released the brakes and as we were adding power and beginning to roll, tower advised us to hold our position, that the clearance was not for us but for air carrier Y XXX. It seems to me that similar call signs occur more often than necessary among different airlines in the same market/time slots.

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Original NASA ASRS Text

Title: AN ACR AT ORD STARTED TO TAKE OFF WHEN THE CREW HEARD A TWR CLRNC FOR ANOTHER FLT WITH A SIMILAR CALL SIGN.

Narrative: WE WERE CLRED ONTO RWY 32L AT INTXN T10 TO HOLD. I WAS EXPECTING A TKOF CLRNC AFTER THE ACFT THAT HAD JUST LANDED CLRED THE RWY. I WAS NOT AWARE THAT TWR WAS WORKING A FLT WITH A SIMILAR CALL SIGN (ACR Y XXX -- WE WERE ACR X YXX) ON THE SAME FREQ, BUT A DIFFERENT RWY. IT IS POSSIBLE THAT MY SITUATIONAL AWARENESS WAS NOT AT AN ALL TIME HIGH DUE TO THE HOUR, BUT IT IS ALSO TRUE THAT NO SPECIAL EFFORT WAS MADE TO MAKE US AWARE OF HIS PRESENCE ON THE FREQ. AT ANY RATE, WE RESPONDED TO WHAT ALL 4 OF US (SO OPERATING EXPERIENCE IN PROGRESS) THOUGHT WAS OUR TKOF CLRNC AND READ IT BACK TO TWR. TWR MADE NO COMMENT AND WE HEARD NO ONE ELSE ACKNOWLEDGE THE CLRNC. WE RELEASED THE BRAKES AND AS WE WERE ADDING PWR AND BEGINNING TO ROLL, TWR ADVISED US TO HOLD OUR POS, THAT THE CLRNC WAS NOT FOR US BUT FOR ACR Y XXX. IT SEEMS TO ME THAT SIMILAR CALL SIGNS OCCUR MORE OFTEN THAN NECESSARY AMONG DIFFERENT AIRLINES IN THE SAME MARKET/TIME SLOTS.

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.