WARNING HORN SOUNDED DURING TKOF ROLL ON ACR MLG. FLT CREW TKOF ABORT AND FOUND TRIM TAB SET OUTSIDE GREEN BAND.

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ON TKOF ROLL AS THROTTLE ADVANCED RECEIVED TKOF WARNING HORN. ABORTED TKOF AT LESS THAN 60 KTS AND ROLLED OFF FIRST TURNOFF. UPON CHKING DISCOVERED TRIM TO BE NEAR AFT EDGE OF GREEN BAND. INITIAL TRIM SETTING HAD BEEN 14.7%. MANIFEST CHK HAD GIVEN REVISED TRIM SETTING OF 10.7%. NORMAL PRACTICE AMONG CREWS ON THIS MLG HAS BEEN TO SET TRIM SLIGHTLY LIGHT (BENEATH) THAT GIVEN TO AID IN MAINTAINING PROPER PITCH UP FOR NOISE ABATEMENT CLBOUT. THE NATURE OF THE TRIM SETTING INDICATION IS NOT VERY PRECISE (CERTAINLY NOT TO TENTHS OF A PERCENT). IN THIS CASE THE SETTING HAD BEEN JUST LOW ENOUGH THAT OUR TENDENCY TO GO TO THE LOWER OF WHERE WE PERCEIVED THE SETTING TO BE HAD PUT US AT THE EDGE OF THE GREEN BAND AND TRIGGERED THE TKOF WARNING. ON THE TXWY WE ADJUSTED THE TRIM; RAN UP THE ENGS; RECEIVED NO WARNING AND THEN PROCEEDED WITH A NORMAL TKOF. IN THE FUTURE ANY TRIM SETTING CLOSE TO THE GREEN BAND EDGE SHOULD BE CHKED CLOSELY--PERHAPS EVEN TO THE POINT OF AN INITIAL RUN UP IN POS BEFORE STARTING ROLL. WHEREAS THE METHOD OF COMPUTING TRIM IS RELATIVELY PRECISE; THE METHOD OF SETTING IS IMPRECISE TO SAY THE LEAST.