TKOF ABORTED DUE TO FLAPS NOT DOWN.

Narrative

CAPT AND COPLT WERE UNFAMILIAR WITH ORD (CAPT HAD LESS EXPERIENCE). DURING PUSHBACK; RWY WAS CHANGED FROM RWY 14R OR RWY 9L TO RWY 27L. BOTH PLTS HAD TRIED TO STUDY POSSIBLE TAXI RTES TO RWY 14R-RWY 19L. AS WE STARTED TAXI TO RWY 27L; COPLT SUGGESTED WE HOLD OFF ON TAXI CHKLIST UNTIL ESTABLISHED ON TAXI RTE. CAPT AGREED. ORD METERING INSTRUCTED US TO TAXI RWY 27L AND CONTACT GND AT A17. GND INSTRUCTED US TO FOLLOW AN ACR 727 APCHING ON TXWY FROM OUR R. CHKLIST WAS CONDUCTED. UPON PWR APPLICATIONS; THE TKOF WARNING INDICATED FLAP CONFIGN. THE FLAPS HAD NOT BEEN EXTENDED. WE TAXIED CLR OF RWY AT M6 AND LOWERED FLAPS; DID CHKLIST AGAIN AND TOOK OFF UNEVENTFULLY. OUR UNFAMILIARITY OF ORD COMBINED WITH THE CHANGES AND MISTAKES LED US TO BE PRE-OCCUPIED. THE COMPLICATED TAXI LED US TO NOT PAY ENOUGH ATTN TO THE ACFT ITSELF. TKOF WARNING SYS WORKED PROPERLY. SUPPLEMENTAL INFO FROM ACN 288147: I MISTAKENLY TURNED R ON BRAVO TO FOX TO M TO FOLLOW ACR B. DURING THE ENSUING DISCUSSION OF OUR MISTAKE IN TAXI; THE CHKLISTS WERE CONDUCTED. READ THE CHKLISTS; BUT DID NOT DO THEM PROPERLY!