Narrative:

Our scheduled flight was from mdw to our next city. Operations at mdw were using runways 31C and 22L for takeoffs and runway 31C circle to land runway 22L. After an on time pushback, we were given taxi clearance to runway 31C via txwys Y, P and G. As we approached runway 31C, we changed over to tower frequency and immediately heard tower say, 'company flight XXXX, if you can get to the runway, we will make a gap.' the first officer answered with a 'roger.' as we taxied up to the runway 31C hold short line, a company aircraft was taking off on runway 31C and another airline was on our right side. A few moments later, we heard tower say, 'company flight XXXX, taxi into position and hold. Be ready, company is on 3 mi final.' the first officer answered with our call sign, 'company flight XXXX position and hold -- we'll be ready.' the next tower transmission was, 'company flight XXXX, cleared for takeoff.' the tower transmission was slightly garbled so I asked the first officer to reconfirm the takeoff clearance. The first officer did so. We then heard, 'cleared for takeoff' (a short pause followed by) 'company flight XXXX -- stop.' I had just started to bring up the power when tower told us to stop, so I immediately reduced the thrust levers to idle and stopped the aircraft. I had not advanced the thrust levers to takeoff thrust and we were not above taxi speed when we stopped. I then told tower we had stopped. Then tower transmitted to a company flight XXXY, which until this time, we didn't even know existed. Company flight XXXY was apparently operating on runway 22L, also. Tower asked who was on runway 31C. Confused by the question, I replied that company flight XXXX was on runway 31C. After some discussion with tower, we cleared the runway at taxiway P. A few mins later, tower cleared us back onto runway 31C for takeoff. We reaccomplished the checklist to include the opc and made an uneventful takeoff and departure. Tower operations were extremely busy during this period and because of this, both the first officer and myself were paying very close attention to the radios. We had done all cockpit procedures by the book. At no time were we told that a company flight XXXY was on tower frequency. At no time did anyone question our responses to tower's radio xmissions. The first time we knew there was even a company flight XXXY was when tower asked us who was on runway 31C. We did not know that tower had been talking to company flight XXXY instead of company XXXX until we arrived at our next city and I talked to the mdw tower supervisor. Without a doubt, the main reason for this incident was the similar sounding call signs. Distinguishing between company flight XXXX and XXXY, one of which was operating on runway 22L, in a clam environment, is difficult enough, but to do it in a congested environment like mdw tower during peak hours at night, departing on 2 runways, is asking for trouble. Ways to prevent this from happening again: first, we should deconflict these call signs as soon as possible and check the entire schedule for any other possible conflicts. Also, ATC should advise aircrews when similar sounding call signs are on their frequency. Finally, everyone should make sure their radio terminology is as clear, concise and as standardized as possible. I have not heard the tape, but I'm sure terminology on both sides of the radio could have been better. In closing, the cadence of radio xmissions and sequence of events led both my first officer and myself to not only believe that we were talking to tower and tower was talking to us, but we were complying with their instructions. Supplemental information from acn 596980: our company flight XXXY aborted takeoff at midway airport runway 22L, because of a possible conflict with another aircraft. The other aircraft, possibly company flight XXXX, may have mistakenly taken active runway 31C. This runway crosses ours about midfield. I believe that tower spotted the other aircraft on the other runway. Tower made an emphatic radio call, 'company flight XXXY stop.' we had just started our roll and made an immediate slow speed (20-30 KTS) reject. We cleared the runway at taxiway P. Until tower's call to stop, I was not aware of the other flight's existence, complex operations. Our company needs to aggressively eliminate similar call sign issues. Tower needs to consider simplifying departure operations. In this case, departures from a single runway, although slower, would have been safer. Supplemental information from acn 596812: numerous xmissions from both tower and other act were overlapping each other. Supplemental information from acn 596982: tower cleared us to 'taxi into position and hold runway 22L, be ready for expeditious, traffic on X mi final.' I read back the complete clearance, including call sign. Tower then cleared us for 'takeoff runway 22L, maintain heading 220 degrees. After reading back the complete clearance (including call sign), we started our takeoff roll. Tower then called a 'company flight XXXY, stop takeoff immediately.' the captain immediately aborted the takeoff at very slow speed, while I was searching the runway for any incursion. After we cleared the active, we found out that company with the call sign 'company flight XXXX' was also on frequency.

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Original NASA ASRS Text

Title: INTXN RWY OPS, SIMILAR ACFT NUMBERS INCIDENT AT MDW RESULTS IN GAR AND 2 ABORTED TKOFS.

Narrative: OUR SCHEDULED FLT WAS FROM MDW TO OUR NEXT CITY. OPS AT MDW WERE USING RWYS 31C AND 22L FOR TKOFS AND RWY 31C CIRCLE TO LAND RWY 22L. AFTER AN ON TIME PUSHBACK, WE WERE GIVEN TAXI CLRNC TO RWY 31C VIA TXWYS Y, P AND G. AS WE APCHED RWY 31C, WE CHANGED OVER TO TWR FREQ AND IMMEDIATELY HEARD TWR SAY, 'COMPANY FLT XXXX, IF YOU CAN GET TO THE RWY, WE WILL MAKE A GAP.' THE FO ANSWERED WITH A 'ROGER.' AS WE TAXIED UP TO THE RWY 31C HOLD SHORT LINE, A COMPANY ACFT WAS TAKING OFF ON RWY 31C AND ANOTHER AIRLINE WAS ON OUR R SIDE. A FEW MOMENTS LATER, WE HEARD TWR SAY, 'COMPANY FLT XXXX, TAXI INTO POS AND HOLD. BE READY, COMPANY IS ON 3 MI FINAL.' THE FO ANSWERED WITH OUR CALL SIGN, 'COMPANY FLT XXXX POS AND HOLD -- WE'LL BE READY.' THE NEXT TWR XMISSION WAS, 'COMPANY FLT XXXX, CLRED FOR TKOF.' THE TWR XMISSION WAS SLIGHTLY GARBLED SO I ASKED THE FO TO RECONFIRM THE TKOF CLRNC. THE FO DID SO. WE THEN HEARD, 'CLRED FOR TKOF' (A SHORT PAUSE FOLLOWED BY) 'COMPANY FLT XXXX -- STOP.' I HAD JUST STARTED TO BRING UP THE PWR WHEN TWR TOLD US TO STOP, SO I IMMEDIATELY REDUCED THE THRUST LEVERS TO IDLE AND STOPPED THE ACFT. I HAD NOT ADVANCED THE THRUST LEVERS TO TKOF THRUST AND WE WERE NOT ABOVE TAXI SPD WHEN WE STOPPED. I THEN TOLD TWR WE HAD STOPPED. THEN TWR XMITTED TO A COMPANY FLT XXXY, WHICH UNTIL THIS TIME, WE DIDN'T EVEN KNOW EXISTED. COMPANY FLT XXXY WAS APPARENTLY OPERATING ON RWY 22L, ALSO. TWR ASKED WHO WAS ON RWY 31C. CONFUSED BY THE QUESTION, I REPLIED THAT COMPANY FLT XXXX WAS ON RWY 31C. AFTER SOME DISCUSSION WITH TWR, WE CLRED THE RWY AT TXWY P. A FEW MINS LATER, TWR CLRED US BACK ONTO RWY 31C FOR TKOF. WE REACCOMPLISHED THE CHKLIST TO INCLUDE THE OPC AND MADE AN UNEVENTFUL TKOF AND DEP. TWR OPS WERE EXTREMELY BUSY DURING THIS PERIOD AND BECAUSE OF THIS, BOTH THE FO AND MYSELF WERE PAYING VERY CLOSE ATTN TO THE RADIOS. WE HAD DONE ALL COCKPIT PROCS BY THE BOOK. AT NO TIME WERE WE TOLD THAT A COMPANY FLT XXXY WAS ON TWR FREQ. AT NO TIME DID ANYONE QUESTION OUR RESPONSES TO TWR'S RADIO XMISSIONS. THE FIRST TIME WE KNEW THERE WAS EVEN A COMPANY FLT XXXY WAS WHEN TWR ASKED US WHO WAS ON RWY 31C. WE DID NOT KNOW THAT TWR HAD BEEN TALKING TO COMPANY FLT XXXY INSTEAD OF COMPANY XXXX UNTIL WE ARRIVED AT OUR NEXT CITY AND I TALKED TO THE MDW TWR SUPVR. WITHOUT A DOUBT, THE MAIN REASON FOR THIS INCIDENT WAS THE SIMILAR SOUNDING CALL SIGNS. DISTINGUISHING BTWN COMPANY FLT XXXX AND XXXY, ONE OF WHICH WAS OPERATING ON RWY 22L, IN A CLAM ENVIRONMENT, IS DIFFICULT ENOUGH, BUT TO DO IT IN A CONGESTED ENVIRONMENT LIKE MDW TWR DURING PEAK HRS AT NIGHT, DEPARTING ON 2 RWYS, IS ASKING FOR TROUBLE. WAYS TO PREVENT THIS FROM HAPPENING AGAIN: FIRST, WE SHOULD DECONFLICT THESE CALL SIGNS AS SOON AS POSSIBLE AND CHK THE ENTIRE SCHEDULE FOR ANY OTHER POSSIBLE CONFLICTS. ALSO, ATC SHOULD ADVISE AIRCREWS WHEN SIMILAR SOUNDING CALL SIGNS ARE ON THEIR FREQ. FINALLY, EVERYONE SHOULD MAKE SURE THEIR RADIO TERMINOLOGY IS AS CLR, CONCISE AND AS STANDARDIZED AS POSSIBLE. I HAVE NOT HEARD THE TAPE, BUT I'M SURE TERMINOLOGY ON BOTH SIDES OF THE RADIO COULD HAVE BEEN BETTER. IN CLOSING, THE CADENCE OF RADIO XMISSIONS AND SEQUENCE OF EVENTS LED BOTH MY FO AND MYSELF TO NOT ONLY BELIEVE THAT WE WERE TALKING TO TWR AND TWR WAS TALKING TO US, BUT WE WERE COMPLYING WITH THEIR INSTRUCTIONS. SUPPLEMENTAL INFO FROM ACN 596980: OUR COMPANY FLT XXXY ABORTED TKOF AT MIDWAY ARPT RWY 22L, BECAUSE OF A POSSIBLE CONFLICT WITH ANOTHER ACFT. THE OTHER ACFT, POSSIBLY COMPANY FLT XXXX, MAY HAVE MISTAKENLY TAKEN ACTIVE RWY 31C. THIS RWY CROSSES OURS ABOUT MIDFIELD. I BELIEVE THAT TWR SPOTTED THE OTHER ACFT ON THE OTHER RWY. TWR MADE AN EMPHATIC RADIO CALL, 'COMPANY FLT XXXY STOP.' WE HAD JUST STARTED OUR ROLL AND MADE AN IMMEDIATE SLOW SPD (20-30 KTS) REJECT. WE CLRED THE RWY AT TXWY P. UNTIL TWR'S CALL TO STOP, I WAS NOT AWARE OF THE OTHER FLT'S EXISTENCE, COMPLEX OPS. OUR COMPANY NEEDS TO AGGRESSIVELY ELIMINATE SIMILAR CALL SIGN ISSUES. TWR NEEDS TO CONSIDER SIMPLIFYING DEP OPS. IN THIS CASE, DEPS FROM A SINGLE RWY, ALTHOUGH SLOWER, WOULD HAVE BEEN SAFER. SUPPLEMENTAL INFO FROM ACN 596812: NUMEROUS XMISSIONS FROM BOTH TWR AND OTHER ACT WERE OVERLAPPING EACH OTHER. SUPPLEMENTAL INFO FROM ACN 596982: TWR CLRED US TO 'TAXI INTO POS AND HOLD RWY 22L, BE READY FOR EXPEDITIOUS, TFC ON X MI FINAL.' I READ BACK THE COMPLETE CLRNC, INCLUDING CALL SIGN. TWR THEN CLRED US FOR 'TKOF RWY 22L, MAINTAIN HDG 220 DEGS. AFTER READING BACK THE COMPLETE CLRNC (INCLUDING CALL SIGN), WE STARTED OUR TKOF ROLL. TWR THEN CALLED A 'COMPANY FLT XXXY, STOP TKOF IMMEDIATELY.' THE CAPT IMMEDIATELY ABORTED THE TKOF AT VERY SLOW SPD, WHILE I WAS SEARCHING THE RWY FOR ANY INCURSION. AFTER WE CLRED THE ACTIVE, WE FOUND OUT THAT COMPANY WITH THE CALL SIGN 'COMPANY FLT XXXX' WAS ALSO ON FREQ.

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.