CAPT FLYING LGT HIT TAIL SKID ON ROTATION.

Narrative

FLT PUSHED FROM GATE WITH A WHEELS-UP TIME OF XX. ATC STRONGLY ADVISED US THAT AN EARLIER WHEELS-UP TIME WAS IMMINENT; SO WE PUSHED AT THE XX TIME. THE DELAYED ENG PROC WAS UTILIZED; AND DURING TAXI WE RECEIVED THE ACARS TKOF. PITCH ATTITUDE OF 15 DEG (3 ENG CLB). TKOF EPR REDUCED AT 190/192/190 WHICH WE USED AND A STABILIZER TRIM OF 6.1. THE TKOF ROLL WAS NORMAL AND NO SIGN OF WIND SHEAR WAS EVIDENT. I WAS FLYING AND AT V1/VR INITIATED A NORMAL ROTATE OF 2 TO 3 DEG PER SECOND TO 15 DEG PITCH ATTITUDE; AS PER SOPA CRITERIA. IMMEDIATELY AFTER LIFTOFF I HEARD A FAINT NOISE WHICH I THOUGHT RESEMBLED THE GEAR STRUT EXTENSION. SO INFORMED ME THAT THE TAIL SKID LIGHT WAS STILL ILLUMINATED. WE ASSUMED THAT THE SKID HAD BEEN STRUCK AND WE WENT TO THE BOOK FOR THE PROC AND FOLLOWED IT. BOTH DISPATCH AND ORD MAINT WERE INFORMED AS TO OUR SITUATION AND WE CHOSE TO PROCEED TO OUR DEST. WE MADE THE APCH AT ORD; RWY 9R; AND LANDED NORMALLY WITH NO FURTHER INCIDENT. IN REVIEWING; THE ACARS WT TAB GIVEN US AT DEP AND THE TAB WE PROCURED AT OUR DEST FROM THE COMPUTER SHOWED A DIFFERENCE OF 400 POUNDS DUE TO; APPARENTLY; 2 ADDITIONAL PAX BOARDING LATE. A MINOR DIFFERENCE; BUT NEVER XMITTED TO US. OTHER THAN THIS; ALL THE WTS; NUMBERS; SPDS; TKOF AND ROTATION PROCS WERE ACCORDING TO SOPA AND CAN BE ATTESTED TO BY MYSELF; FO; AND SO. IN CONCLUSION; THE LGT WITH XXX ENGS; WHEN NEW; WAS AN UNDERPWRED ACFT; AND NOW AFTER YRS OF USE AND THOUSANDS OF ENG CYCLES; THESE ENGS DO NOT DEVELOP THE SAME PWR AND THRUST NUMBERS REPRESENTED IN THE QUICK REF MANUAL; ESPECIALLY AT REDUCED EPR. IT IS MY RECOMMENDATION; IF YOU WILL; TO ELIMINATE REDUCED PWR SETTINGS AND/OR SLOW THE ROTATION RATE TO 2 DEG PER SECOND MAX (AS OPPOSED TO 2-3 DEG PER SECOND PER SOPA) UNTIL THERE IS FURTHER INVESTIGATION.