UNAUTH INTXN TKOF DURING A NIGHT OP.

Narrative

WE WERE CLRED TO TAXI TO RWY 27L AND GIVEN A EDC TIME OF XA17Z (52 MINS AFTER PUSHBACK). WE WERE IN THE RWY 27L HOLDING PAD FACING S. AT XB05Z WE WERE GIVEN A NEW EDC OF XB10Z. WE STARTED OUR ENGS AND WHEN READY WERE GIVEN TAXI TO AND CLRED FOR TKOF ON RWY 22L. WE CHKED OUR TPS AND ALL DATA FOR STANDARD PWR WAS THE SAME FOR RWY 22L. I SAW THE RED RWY 4R-22L SIGN AHEAD AND THE NORMAL PICTURE OF THE END OF THE RWY WAS IN MY MIND. I MADE THE L TURN ON THE END FROM THE SLIGHT ANGULAR APCH TO MAKE THE 90 DEG R TURN FOR LINEUP. I GAVE THE ACT TO THE COPLT AND TKOF WAS INITIATED. AT APPROX 100 KIAS TWR CALLED TO SAY HE THOUGHT WE STARTED TKOF AT S5 INTXN AND ASKED IF WE HAD ENOUGH RWY TO TKOF. AS A PRECAUTION I SELECTED TKOF ON THE TRI (MAX PWR) AND BASED ON WT; AIRSPD AND RWY REMAINING I DECIDED TO CONTINUE TKOF RATHER THAN MAKE A HIGH SPD ABORT. LIFTOFF OCCURRED WITH APPROX 3000 FT REMAINING. WE WERE NOT SURE EVEN AFTER ANALYZING THE SIT LATER IN THE FLT THAT WE HAD REALLY USED THE S5 INTXN. AFTER MUCH DELIBERATION WE FELT THIS RPT SHOULD BE MADE IN THE INTEREST OF PREVENTING SIMILAR OCCURRENCES. THE MAIN REASON I FEEL AN ERROR MAY HAVE BEEN MADE WAS NOT ANTICIPATING TKOF ON RWY 22L. MY BELIEF THAT I WAS AT THE END OF RWY 22L WAS BACKED UP BE SEEING THE RED RWY 4R-22L SIGN. I DON'T KNOW IF THERE IS A YELLOW S5 SIGN AT THAT INTERSECTION. IF NOT; MAYBE THAT SHOULD BE LOOKED INTO. SUPPLEMENTAL INFO FROM ACN 297857: THE CAPT TAXIED TOWARD RWY 22L; TWR ASKED IF WE WERE TAXING ONTO RWY 22L; I CONFIRMED THE TKOF CLRNC PRIOR TO TAXING ON THE RWY. I ASKED FOR THE LATEST WIND INFO AND COMPLETED THE CHKLIST ITEMS. AFTER RWY LINEUP THE CAPT TRANSFERRED THE ACFT TO ME. I CHKED OUR HDG TO ENSURE WE WERE ON THE PROPER RWY. AFTER CLBOUT WE DISCUSSED THE SIT AND WERE STILL UNSURE IF WE USED S5 INTXN. AFTER SOME DELIBERATION WE DECIDED THIS RPT SHOULD BE MADE IN THE INTEREST OF PREVENTING SIMILAR OCCURRENCES.