A RPTR PLT OF B757 FLYING INTO JFK; RECEIVES A PREMATURE LOC CAPTURE SIGNAL ON THE FLT DIRECTOR WHICH INDICATES A TURN THAT WOULD TAKE HIM ABOUT 5 MI TO THE S OF THE ARPT.

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XA29Z; JFK TWR; 2000 FT; JFK RWY 31R. ON APPROX 010 DEG HDG TO RWY 31R; LOC ACFT FLT DIRECTOR COMMANDED L TURN-IN PREMATURELY; ABOUT 5 MI S OF MALDE INTXN. ADI LOC CAPTURE ANNUNCIATED PREMATURELY. ALSO ALL FREQS AND IDENTS CHKED OK. CONTINUED ON HDG UNTIL PROPER RWY 31R LOC CAPTURE. THIRD TIME IN 2 WKS -- WAS NOT DRINKING TOO MUCH EGG NOG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR HAS HAD THIS HAPPEN ON 3 DIFFERENT DAYS. ALTHOUGH IT WAS IN THE SAME TYPE OF ACFT; B757; IT WAS IN DIFFERENT N-NUMBERS OF THE B757. ALL APCHS WERE IN VMC. THE ILS WAS ARMED FOR THE APCH. AS THE ILS LOC WOULD SWING ACROSS HIS DISPLAY AND THE CAPTURE INDICATION WOULD ILLUMINATE; HE WOULD DISCONNECT BOTH FLT DIRECTORS AND REARM THEM FOR THE PROPER ILS. FURTHER; HE STATED THE FLT DIRECTOR HELD THIS INDICATION FOR ABOUT 30-60 SECONDS BEFORE HE WOULD DISENGAGE AND RE-ENGAGE FOR THE PROPER INTERCEPT. IF HE WERE TO FOLLOW THE INDICATIONS; HE FELT IT WOULD TAKE HIM ABOUT 5 MI TO THE L OF THE ARPT. IT IS DIFFICULT TO TELL HOW FAR TO THE L IT MIGHT BE WITHOUT FLYING THE INDICATIONS; SO THE 5 MI IS AN ESTIMATE. ON 3 OTHER OCCASIONS WHERE THIS HAPPENED; RPTR WAS FLYING IN VISUAL CONDITIONS; SO RPTR NEVER FLEW THE FLT DIRECTOR INDICATIONS AS HE COULD SEE THAT THEY WOULD NOT TAKE HIM TO THE ARPT.