A 100000 LB ERROR IN TKOF PERFORMANCE CALCULATIONS LED TO EARLY ROTATION AND SUBSEQUENT TAIL SKID STRIKE ON B767- 300.

Narrative

DUE TO TIME COMPRESSION; I BECAME TASK RUSHED AND SELECTED A WT AND SPD CARD THAT A PREVIOUS CREW USED TO LAND. THIS WT WAS APPROX 100000 LBS LIGHTER THAN ACTUAL. THE 25 NUMBER ON THE CARD WAS OBSCURED. REFS TO THE WT VIA CHKLISTS WERE TO THE CDU NOT THE CARD. MY MISTAKE WAS THE PRINCIPLE CAUSE OF THE INCIDENT. THE CAPT MADE THE TKOF. HE REALIZED SOMETHING WAS NOT CORRECT AT ROTATION. HE HELD THE ACFT IN A 'CHKED' ATTITUDE UNTIL THERE WAS MORE AIRSPD. REGARDLESS; WE STILL BARELY STRUCK THE TAIL SKID (NOT THE TAIL). BASED ON NORMAL RETRACTION AND EYE WITNESS ACCOUNT; WITH THE ADVISE AND CONCURRENCE OF THE DISPATCHER; MAINT AND DUTY MGR; THE CAPT ELECTED TO CONTINUE TO SFO. PREDICATED ON PREVIOUS ACFT INCIDENTS ETC; I STRONGLY ADVISED THE CAPT TO RETURN TO LHR. HE CONSIDERED IT AND DUE TO PREVIOUSLY DESCRIBED EVENTS; ELECTED TO CONTINUE AND ADVISED ME THAT MY INPUT WAS 'DULY NOTED' AND HE ALONE WOULD TAKE RESPONSIBILITY FOR THE DECISION. I THEN CONSIDERED IT MORE RESPONSIBLE TO AID THE CAPT AS BEST I COULD. THE CAPT'S FLT SKILLS AND JUDGEMENT PREEMPTED MY ERROR FROM ALLOWING A SEVERE SIT TO DEVELOP.