B747-400 HAS POTENTIAL GND ENCOUNTER WITH PUSH BACK TUG AFTER RECEIVING SALUTE.

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WE PUSHED BACK; STARTED ENGS; AND RECEIVED THE 'SALUTE AND RELEASE FROM GUIDANCE.' I CALLED FOR TAXI CLRNC; AND WHEN RECEIVED; I SAID CLR L; LOOKED L; THEN LOOKED R AS MY FO LOOKED R AND WE BOTH NOTICED THE TUG VEHICLE VERY CLOSE TO THE R WING FACING THE SAME DIRECTION AS THE AIRPLANE. I ASKED THE FO IF THE TUG WAS UNDER THE WING OR WAS OUTSIDE IT. SHE SAID SHE THOUGHT IT WAS OUTSIDE; JUST BARELY; AND I BELIEVED THAT TO BE CORRECT AS WE HAD RECEIVED THE SALUTE AND RELEASE. IN THE 5-10 SECONDS THAT WE SPENT BRIEFLY DISCUSSING THE TUG CLRNC; HE; AND I STILL CAN'T BELIEVE THIS; BEGAN TO DO A 180 DEG TURN; INTO THE ACFT; TURNING L AND GOING UNDER THE WING. IT IS MY CERTAIN OPINION THAT IF I HAD BEGUN TO TAXI AS THE NORMAL TIME SEQUENCE WOULD DICTATE; I WOULD HAVE PROBABLY STRUCK THE TUG WITH THE R OUTBOARD ENG. IT WAS ONLY THE 5-10 SECOND DELAY WE TOOK DISCUSSING THE TUG CLRNC THAT PROBABLY PREVENTED A POSSIBLE SERIOUS INJURY TO THE TUG DRIVER AND DAMAGE TO THE ACFT. I BELIEVE THAT THE TUG CREWS NEED CONSTANT REVIEW ON THE SERIOUS NATURE OF SAFETY COMPLIANCE. THEY TEND TO GET VERY MOTIVATED TO DO A GOOD JOB BUT I BELIEVE THEY LOSE SIGHT OF SAFETY FIRST. THEY NEED TO BE REPEATEDLY BRIEFED THAT A 'SALUTE AND RELEASE' MEANS THAT ALL PERSONNEL AND VEHICLES ARE CLR OF THE ACFT AND WILL REMAIN CLR. NO EXCEPTIONS. IF A VEHICLE IS NOT CLR THEN THEY CANNOT GIVE THE SALUTE AND RELEASE.