ACR X TKOF ON OCCUPIED RWY HAD LTSS FROM ACR Y. SYS ERROR. NIGHT OP.

Narrative

ACR Y AHEAD; A B-727; WAS CLRED FOR TKOF. ACR X CLRED INTO POS AND HOLD. AS WE WERE TURNING ONTO THE RWY WE WERE TOLD TFC AHEAD IS A R TURNOUT -- YOU ARE CLRED FOR TKOF; STRAIGHT OUT. WE ADDED PWR -- CHKED THE INSTS; IT WAS NIGHT. AT 80 KTS; THRUST NORMAL. WE REALIZED ACFT AHEAD WAS STILL ON RWY; APPEARED TO BE ROTATING FOR TKOF. WE WERE APPROX 25800 LBS LESS THAN MAX GROSS WT SO I BELIEVE WE WERE STARTING OUR ROTATION ABOUT 4000 FT DOWN THE RWY. ACFT AHEAD ROLLED APPROX 10000 FT. I BELIEVE HE WAS DOING A FLAPS 5 DEG TKOF AND WAS HVY. HE DEPARTED RWY AT THE END. WE DEPARTED THE RWY APPROX MID FIELD. OUR CLB RATE WAS MUCH STEEPER SO WE NEEDED TO LOOK OVER THE NOSE TO KEEP HIM IN SIGHT. THE DANGER IN THE SIT WOULD BE IF THE FIRST ACFT ABORTED HIS TKOF AND THE SECOND ACFT NEEDED TO ALSO. 2 ACFT TRYING TO STOP ON THE END OF 1 RWY COULD BE DISASTROUS. IT IS DIFFICULT TO TELL AT NIGHT IF THE ACFT AHEAD IS REALLY AIRBORNE UNTIL IT IS 50 FT OR SO IN THE AIR. FROM THE TWR PERSPECTIVE; I DOUBT THEY CAN TELL IF AN ACFT IS AIRBORNE UNTIL IT MAY BE HIGHER THAN THAT. ALSO; THEY MAY ASSUME THAT SAME TYPE ACFT WOULD HAVE SIMILAR TKOF ROLL -- WHICH IS NOT TRUE BECAUSE OF DIFFERENT LOADS AND FLAP SETTINGS. WHILE I LIKE TO SEE TFC MOVED EFFICIENTLY; SAFETY IS OF THE UTMOST IMPORTANCE. TO PREVENT A RECURRENCE -- DON'T TAKE OFF -- UNTIL YOU ARE SURE ACFT AHEAD IS AIRBORNE. FOR TWR -- IF THEY KNEW ESTIMATED TKOF ROLL OF THE DEPARTING ACFT -- MAY HELP THEM IN THEIR SPACING PROBS.