ACR STARTED UNAUTHORIZED TKOF.

Narrative

FO READ BACK CLRNC THAT WAS ISSUED TO ACFT Y IN POS FOR TKOF ON 5R. COMPANY Y ALSO ACCEPTED CLRNC FOR TKOF AND DID NOT RESPOND. MY FO READ BACK TKOF CLRNC USING OUR FULL CALL SIGN; AND WE BEGAN TKOF ROLL AT SAME TIME AS COMPANY TRIP Y. TWR ASKED US TO CANCEL OUR TKOF CLRNC. WE ABORTED PRIOR TO REACHING 70 KTS. CTLR HAD NOT CAUGHT THE INCORRECT CALL SIGN ON THE READBACK (TWR TAPE RECORDING DOES INDICATE THAT WE READ BACK CLRNC WITH NO ACKNOWLEDGEMENT FROM TWR CTLR). TWR SUPVR; WORKING GND CTL AT THE TIME; NOTICED BOTH BEGINNING TKOF ROLL AT SAME TIME AND POINTED IT OUT TO THE TWR CTLR. THE ERROR WAS CAUGHT EARLY ENOUGH THAT NO SEPARATION OR MISHAP OCCURRED. IT WAS BASICALLY A BREAKDOWN IN COMS. I CONTRIBUTED TO THE ERROR BY NOT QUESTIONING THE CLRNC THE FO READ BACK WHILE I WAS CONCENTRATING ON TAXIING INTO TKOF POS. ACTUALLY; I DO NOT RECALL HEARING THE CTLR ISSUE THE CLRNC; JUST THE FO READING IT BACK. I SHOULD HAVE QUESTIONED IT EVEN MORE BECAUSE IT WAS A TKOF ON 5L WITH A R TURN TO 095 DEGS. THAT SHOULD HAVE CLUED ME IN; BUT I MISSED IT. WE TAXIED CLR AND REJOINED SEQUENCE FOR DEP. SUPPLEMENTAL INFO FROM ACN 197865: OUR FLT; ACR X; WAS CLRED INTO POS AND HOLD ON RWY 5L. AFTER RECEIVING TKOF CLRNC I REPLIED 'CALL SIGN CLRED FOR TKOF 5L; R TURN 095 DEGS.' AT APPROX 70 KTS; TWR INSTRUCTED US TO CANCEL TKOF CLRNC. WE ABORTED TKOF WITHOUT INCIDENT. WE WERE THEN INFORMED THAT THE TKOF CLRNC WAS FOR COMPANY TRIP Y (WHO WAS ROLLING ON RWY 5R). AFTER COMPLETING ALL APPROPRIATE CHKLISTS WE THEN DEPARTED RWY 5L FOR ORD. WHILE AT ORD; WE CONTACTED CLE TWR TO VERIFY CLRNC. AFTER LISTENING TO THE CTL TWR TAPE IT WAS VERIFIED THE TKOF CLRNC WAS ISSUED TO ACR Y. ACCORDING TO THE TAPE; Y NEVER ACKNOWLEDGED TKOF CLRNC AND THE TWR CTLR FAILED TO DETECT MY ACKNOWLEDGEMENT OF Y'S CLRNC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR GAVE INFO REF OTHER ACFT Y. SAYS ATC TWR SUPVR INDICATED THAT THERE WOULD BE NO FOLLOW-UP ACTION BY FAA AS A RESULT OF THE INCIDENT. RPTR THINKS THAT LOW EXPERIENCE LEVEL OF HIS FO IN MLG ACFT WAS A BIG FACTOR. BELIEVES THAT TKOF CLRNC WAS FOR ACFT Y; BUT ACFT X FO TOOK THE CLRNC AND ACKNOWLEDGED FOR IT. THEN LCL CTLR FAILED TO NOTE THAT WRONG CALL SIGN ACFT READ BACK THE TKOF CLRNC. RPTR (PIC) SAYS HE SHOULD HAVE QUESTIONED THE CLRNC WHICH CONTAINED THE INSTRUCTION TO TURN R HDG 095. THE HDG WAS NOT APPROPRIATE FOR DEP OFF 5L RWY.