A B737-300 PIC TURNS OFF THE LOC FOR RWY 25L TOO SOON WHEN READING 6 DME ON BLD VOR INSTEAD OF THE REQUIRED 6 DME OFF THE VOR AT LAS; NV.

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INBOUND TO LAS ON NOOTN 3; LNDG RWYS 1L&R. INSTRUCTED TO INTERCEPT RWY 25L LOC; TRACK INBOUND TO 6 MI FROM LAS AND THEN TURN 190 DEGS DOWNWIND RWY 1L. INSTEAD OF TURNING AT 6 NM FROM LAS TO 190 DEGS; STARTED TURN AT 6 NM OFF OF BOULDER CITY VOR. AFTER APPROX 30 DEGS OF TURN; APCH ASKED WHAT WE WERE DOING; SAID 'TURNING 190 DEGS;' AT WHICH TIME THEY GAVE FLY 230 DEGS. I CONFIRMED THAT I HAD HEARD THE INSTRUCTIONS CORRECTLY AND THEN REALIZED I WAS ON THE WRONG NAVAID. APCH SAID 'NO PROB OR CONFLICT.' WERE TOLD TO LOOK FOR B767 TO FOLLOW VISUAL RWY 14. UNEVENTFUL APCH AND LNDG. FACTORS: MAIN FACTOR OF COURSE; WRONG NAVAID. CONTRIBUTORY FACTORS: USED LNAV TO TRACK INBOUND RWY 25L LOC; BOTH PLTS HAD BEEN ON BLD VOR TO MONITOR LNAV COURSE TRACKING ON NOOTN ARR. TURNING INBOUND; FO WAS UPDATING INFO TO REFLECT RWY 1L/R INSTEAD OF NORMAL RWY 25L; THEREFORE; HE WAS IN THE COMPUTER AND NOT MONITORING NAV AT THAT MOMENT. WHEN ESTABLISHED ON RWY 25L LOC USING LNAV; SWITCHED TO 111.75 AND VOR/LOC TO TRACK INBOUND OF NEW DME. FAILED TO SWITCH SECOND FREQ TO 116.9; READ 6 DME OFF 116.7 AND THE REST IS HISTORY. FLT CONDITIONS WERE CLR WITH REDUCED VISIBILITY IN HAZE AND SUN DIRECTLY IN YOUR EYES (IE; COULD NOT SEE LAS ARPT OR CITY -- BASICALLY IMC). COULD IT HAPPEN AGAIN? YOU BET. USING LNAV TO NAV ON NOOTN TOLD TO INTERCEPT A NON DME LOC AND TURN AT A POINT OFF A VOR WHICH FREQ IS .20 DIFFERENT FROM NAVAID PREVIOUSLY USED. YES IT WOULD BE NICE IF BLD 116.7 AND LAS 116.9 FREQS WERE NOT EASILY MISINTERPED BECAUSE OF THEIR SIMILAR FIRST 3 NUMBERS. BOTTOM LINE: ME -- THE PF -- SCREWED UP; KEPT EXPECTING TO SEE THE ARPT AND DIDN'T AND USED WRONG NAVAID. MY BACKUP -- THE FO WAS IN THE COMPUTER AND ALSO ON BLD VOR SO WHEN I TURNED AT 6 DME IT LOOKED RIGHT TO HIM.