B757 PLT ON DOWNWIND TO ANC DESCRIBED TCAS TA EVENT AT 2500 DURING VISUAL APCH WHEN FOLLOWING TFC ACTIVATED TCAS.

Narrative

THIS WAS A TROUBLING INCIDENT THAT I FEEL REQUIRES ACTION ON ATC PROCS. WE WERE ON A DOWNWIND VECTOR FOR RWY 7R AT ANC. ANOTHER ACFT WAS ON A DISTANT DOGLEG FINAL FOR RWY 7R. ATC CLRED US FOR THE VISUAL APCH FROM OUR DOWNWIND HDG AND TOLD US THAT THE OTHER ACFT HAD US IN SIGHT AND WOULD FOLLOW US. THIS IS ALL AT NIGHT WITH NO MOON (BUT CLR SKIES). UPON CLRNC FOR THE VISUAL; THE CAPT (IN MY ACFT) EXTENDED HIS DOWNWIND LEG ANOTHER MI OR TWO BEFORE TURNING BASE. THE CAPT WAS ALSO FLYING A CONSERVATIVE APCH AND WAS AT 180 KIAS NOW 8 NM FROM THE FIELD. BEFORE TURNING BASE; THE OTHER ACFT WAS ABOUT 6 NM AWAY. AFTER TURNING BASE; THE OTHER ACFT WAS ABOUT 2.5 NM AWAY AND ALL LOOKED GOOD. WE THEN GOT A TA (SURPRISINGLY NOT AN RA) AND NOTICED THE OTHER ACFT OFF OUR L WING ABOUT 1000 FT. WE TURNED AWAY FROM THEM AND THEN NOTICED HIS TCAS RETURN RAPIDLY DROP BACK TO 2 NM (HE MUST HAVE DONE AN AGGRESSIVE MANEUVER). EVERYONE LANDED UNEVENTFULLY. THE POINT I WANT TO BRING OUT IN THIS IS THAT AT NIGHT; ONE CANNOT DETERMINE ONE'S DISTANCE OR CLOSURE TO ANOTHER ACFT NOR THE HDG OF ANOTHER ACFT. THE CREW THAT SAID THEY WOULD FOLLOW US HAD NOTHING BUT A FEW AIRPLANE LIGHTS TO FOLLOW AND HE HAD NO IDEA OF THE CLOSURE UNTIL TOO LATE. THIS COULD HAVE BEEN AN NMAC ON A CLR NIGHT. I WOULD SUGGEST THAT ATC NOT BE ALLOWED TO ISSUE FOLLOW ANOTHER ACFT CLRNCS AT NIGHT UNLESS THEIR HDGS ARE NEARLY ALIGNED WITH THE RWY AND THE AIRSPD OF THE LEAD ACFT IS GIVEN TO THE TRAILING ACFT AS AN ADVISORY.