Narrative:

We were cleared into position and hold on runway 4R at mdw. I called for the below the line checklist. As we were taxiing onto the runway, doing the checklist, we heard tower tell us to turn left to a heading, which I missed, and cleared for takeoff. The first officer replied, 'company number turn left to 025 degrees and cleared for takeoff.' I wasn't sure of the heading, so I questioned the first officer. He stated that it was 025 degrees and had already set 025 degrees in the heading select window. I advanced the thrust levers and pushed up toward takeoff thrust, as I called set takeoff thrust, I saw a company airplane rolling through the intersection, taking off on runway 31C. I immediately realized that we had accepted his takeoff clearance and aborted the takeoff. The tower noticed us rolling on runway 4R and asked us to clear the runway. An airplane was taxiing on taxiway Y approaching taxiway K, so we taxied up to, and cleared, at runway 31L. The airspeed had not yet come off the peg when we aborted and a check of the opc indicated that we did not have a brake cooling problem, so we taxied back to runway 4R and made an uneventful takeoff. When I got to tpa I called the mdw tower and he said that the other flight's transmission had overridden ours. I think several things contributed to this incident: similar sounding call signs and using crossing runways. The call signs were similar and easy to confuse, especially while doing the checklist. I don't know if we were still on ground frequency when the other flight was cleared onto runway 31C, but an advisory of traffic departing runway 31C when we were cleared onto runway 4R would have helped. This also emphasizes the need to 'listen up,' particularly when the airport is using crossing runways. I also should have had the first officer reconfirm the heading with the tower, that would have gotten us all on the same game page. I certainly will not hesitate to reconfirm any clrncs that I have the slightest doubt about from now on. Supplemental information from acn 579210: the rest of the flight was uneventful. I believe I mistakenly read back company number's takeoff clearance, and when I read it back, tower didn't hear me because I was cutout by company reading back his takeoff clearance. The call came right in the middle of the 'below the line' portion of the pre takeoff checklist, and I should have noticed the 025 degree heading looked unusual (pointed to the north side of downtown). Lessons learned: prioritize. If given a clearance for takeoff (at a high volume airport, with crossing runways, or multiple parallel runways), while accomplishing the remainder of the pre takeoff checklist, finish the checklist, then respond to the takeoff clearance. Anytime there is a question about a heading, altitude, or clearance, query the controller. Radio calls are free!

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Original NASA ASRS Text

Title: B737 FLT CREW ATTEMPTS TO TAKE OFF USING ANOTHER ACFT'S CLRNC AND REJECTS THE TKOF WHEN THE OTHER ACFT IS OBSERVED ROLLING ON A XING RWY AT MDW.

Narrative: WE WERE CLRED INTO POS AND HOLD ON RWY 4R AT MDW. I CALLED FOR THE BELOW THE LINE CHKLIST. AS WE WERE TAXIING ONTO THE RWY, DOING THE CHKLIST, WE HEARD TWR TELL US TO TURN L TO A HEADING, WHICH I MISSED, AND CLRED FOR TKOF. THE FO REPLIED, 'COMPANY NUMBER TURN L TO 025 DEGS AND CLRED FOR TKOF.' I WASN'T SURE OF THE HEADING, SO I QUESTIONED THE FO. HE STATED THAT IT WAS 025 DEGS AND HAD ALREADY SET 025 DEGS IN THE HEADING SELECT WINDOW. I ADVANCED THE THRUST LEVERS AND PUSHED UP TOWARD TKOF THRUST, AS I CALLED SET TKOF THRUST, I SAW A COMPANY AIRPLANE ROLLING THROUGH THE INTXN, TAKING OFF ON RWY 31C. I IMMEDIATELY REALIZED THAT WE HAD ACCEPTED HIS TKOF CLRNC AND ABORTED THE TKOF. THE TWR NOTICED US ROLLING ON RWY 4R AND ASKED US TO CLR THE RWY. AN AIRPLANE WAS TAXIING ON TXWY Y APCHING TXWY K, SO WE TAXIED UP TO, AND CLRED, AT RWY 31L. THE AIRSPD HAD NOT YET COME OFF THE PEG WHEN WE ABORTED AND A CHK OF THE OPC INDICATED THAT WE DID NOT HAVE A BRAKE COOLING PROB, SO WE TAXIED BACK TO RWY 4R AND MADE AN UNEVENTFUL TKOF. WHEN I GOT TO TPA I CALLED THE MDW TWR AND HE SAID THAT THE OTHER FLT'S XMISSION HAD OVERRIDDEN OURS. I THINK SEVERAL THINGS CONTRIBUTED TO THIS INCIDENT: SIMILAR SOUNDING CALL SIGNS AND USING XING RWYS. THE CALL SIGNS WERE SIMILAR AND EASY TO CONFUSE, ESPECIALLY WHILE DOING THE CHKLIST. I DON'T KNOW IF WE WERE STILL ON GND FREQ WHEN THE OTHER FLT WAS CLRED ONTO RWY 31C, BUT AN ADVISORY OF TFC DEPARTING RWY 31C WHEN WE WERE CLRED ONTO RWY 4R WOULD HAVE HELPED. THIS ALSO EMPHASIZES THE NEED TO 'LISTEN UP,' PARTICULARLY WHEN THE ARPT IS USING XING RWYS. I ALSO SHOULD HAVE HAD THE FO RECONFIRM THE HEADING WITH THE TWR, THAT WOULD HAVE GOTTEN US ALL ON THE SAME GAME PAGE. I CERTAINLY WILL NOT HESITATE TO RECONFIRM ANY CLRNCS THAT I HAVE THE SLIGHTEST DOUBT ABOUT FROM NOW ON. SUPPLEMENTAL INFO FROM ACN 579210: THE REST OF THE FLT WAS UNEVENTFUL. I BELIEVE I MISTAKENLY READ BACK COMPANY NUMBER'S TKOF CLRNC, AND WHEN I READ IT BACK, TWR DIDN'T HEAR ME BECAUSE I WAS CUTOUT BY COMPANY READING BACK HIS TKOF CLRNC. THE CALL CAME RIGHT IN THE MIDDLE OF THE 'BELOW THE LINE' PORTION OF THE PRE TKOF CHKLIST, AND I SHOULD HAVE NOTICED THE 025 DEG HDG LOOKED UNUSUAL (POINTED TO THE N SIDE OF DOWNTOWN). LESSONS LEARNED: PRIORITIZE. IF GIVEN A CLRNC FOR TKOF (AT A HIGH VOLUME ARPT, WITH XING RWYS, OR MULTIPLE PARALLEL RWYS), WHILE ACCOMPLISHING THE REMAINDER OF THE PRE TKOF CHKLIST, FINISH THE CHKLIST, THEN RESPOND TO THE TKOF CLRNC. ANYTIME THERE IS A QUESTION ABOUT A HEADING, ALT, OR CLRNC, QUERY THE CTLR. RADIO CALLS ARE FREE!

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.