A POTENTIAL CONFLICT OCCURS BTWN A B757 ON A VISUAL APCH TO RWY 19L AND A TRANSITING HELI N OF THAT RWY AT LAS; NV.

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FPR FILED FOR A KSINO 1 RNAV ARR PROC INTO LAS. LAS ARR ATIS TIME XA54Z; RPTED VISUAL APCHS IN USE TO RWY 25L. FMC PROGRAMMED FOR THE KSI25B RNAV APCH TO RWY 25L. ON CHK-IN WITH LAS APCH; THE CTLR DIRECTED US TO PROCEED DIRECT TO THE WHSKY INTXN AND THEN A 250 DEG HDG AFTER WHSKY FOR A VISUAL APCH TO RWY 19L. AFTER REPROGRAMMING THE FMC; THE PF NOTICED THAT WE WERE NOW HIGH ON THE VNAV PTH DSCNT PROFILE AND REQUESTED A LOWER ALT. ON THE DSCNT TOWARD 7000 FT; APCH ISSUED FURTHER DSCNT CLRNC TO 5100 FT. SOMEWHERE ABOVE 5100 FT AND ON THE 250 DEG HDG ASSIGNED; APCH ASKED IF WE HAD THE ARPT IN SIGHT TO OUR L. WE RESPONDED IN THE AFFIRMATIVE AND APCH THEN CLRED US FOR THE VISUAL APCH TO RWY 19L. AT THIS POINT ON THE APCH; ON THE ASSIGNED HDG OF 250 DEGS; WE WERE 80 DEGS OFF THE FINAL APCH COURSE; JUST OUTSIDE OF THE FAF; JABNA; AND THE VTK ERROR IN THE FMC STILL SHOWED US HIGH ON THE VNAV PTH PROFILE. WE IMMEDIATELY ADVISED APCH THAT WE NEEDED A VECTOR OFF COURSE FOR FURTHER DSCNT AS WE WERE PRESENTLY TOO HIGH FOR A STABILIZED APCH AT THE POINT APCH CTL CLRED US FOR THE VISUAL. APCH ISSUED A R TURN TO A HDG OF 310 DEGS FOR VECTORS ACROSS THE FINAL APCH COURSE FOR FURTHER DSCNT. DURING THE R TURN OFF COURSE AND PRIOR TO REACHING THE 310 DEG HDG ASSIGNED; THE PF REVERSED COURSE BACK TOWARD THE FINAL APCH COURSE TO LIMIT THE OVERSHOOT OF RWYS 19L&R. APCH CTL THEN RECLRED US FOR THE VISUAL APCH TO RWY 19L AND ADVISED US TO SWITCH TO TWR FREQ. DURING THE L TURN BACK TOWARD JABNA AND THE FINAL APCH COURSE; DSNDING TOWARD 2300 FT; WE RECEIVED A TCASII RA OF 'MONITOR VERT SPD.' ON INITIAL CONTACT WITH LAS TWR; WE WERE TOLD NOT TO OVERSHOOT RWYS 19L&R DUE TO HELI TFC AT OUR 1 O'CLOCK POS LOW. THE FO HAD VISUAL CONTACT WITH THE CONFLICTING HELI TFC TO OUR R. UPON COMPLIANCE WITH THE TCASII RA; WE IMMEDIATELY RECEIVED A 'CLR OF CONFLICT' MESSAGE. TWR THEN ISSUED LNDG CLRNC TO RWY 19L. ACFT WAS CONFIGURED; STABILIZED AND ON THE PAPI GLIDE PATH BY 1000 FT AGL. LNDG WAS UNEVENTFUL. LAS APCH CTL; CHANGING THE PLANNED AND FORECAST ARR PROC AND RWY IN CLOSE TO THE ARPT. DURING AND AFTER OUR ARR; ACFT WERE STILL ARRIVING AND LNDG ON THE FORECAST RWY OF RWY 25L. WE WERE PULLED OFF THE NORMAL ARR FOR REASONS UNKNOWN. APCH CTL DID NOT PROVIDE ADEQUATE VECTORS AND SEQUENCING FOR A STABILIZED APCH. LAS APCH CTL WAS SEEMINGLY UNAWARE OF THE HELI TFC UNDER TWR CTL AND OPERATING IN CLOSE PROX TO AN ACTIVE RWY. WHAT IS THE PURPOSE AND USE OF AN RNAV ARR PROC IF APCH CTL MODIFIES OR CHANGES THE ARR PROC ALREADY PROGRAMMED IN THE ACFT'S FMC CLOSE IN TO THE ARPT. I SHOULD HAVE ELECTED TO EXECUTE A MISSED APCH AND ASKED FOR VECTORS OUT OF THE APCH SEQUENCE IN ORDER TO PROPERLY PREPARE AND BRIEF THE APCH ASSIGNED.