A B737-300 CREW ATTEMPTS TO APCH AND LAND RWY 19L AT LAS AFTER THEY HAD BEEN ASSIGNED AND ACKNOWLEDGED RWY 25L FOR LNDG. A POTENTIAL CONFLICT OCCURS ON THAT APCH.

Narrative

ON FUZZY ARR FROM NW (OAK) APCHING LAS; ATIS INFO SHOWED GUSTY WINDS FROM S; LNDG RWY 19L/R LAS WITH 'RWY 25L AVAILABLE ON REQUEST.' APCH GAVE US DSCNT TO 10000 FT; 'EXPECT VISUAL TO RWY 19L.' ABEAM LAS; GIVEN DSCNT TO 8000 FT; THEN 5600 FT. ABOUT 8 NM E; CLRED 'VISUAL APCH TO RWY 25L.' FO ACKNOWLEDGED 'VISUAL TO RWY 25L;' HOWEVER BOTH PLTS WERE EXPECTING RWY 19L AND CONTINUED APCH PROFILE TO THAT RWY UNTIL AFTER SWITCHING TO TWR AND GIVEN CLRNC TO LAND ON RWY '25L.' REALIZING THIS WAS A DIFFERENT RWY THAN THEY WERE HEADED TOWARDS; FO ATTEMPTED TO CLARIFY 'UNDERSTAND CLRED TO LAND RWY 19L.' TWR RECONFIRMED 'RWY 25L.' ABOUT THIS TIME TCASII TFC ALERT SOUNDED FOR ACFT AT R; 3 O'CLOCK; DIRECTING A DSCNT. CREW TURNED L AND CLBED TO CLR TFC (WHICH WAS ON STRAIGHT-IN TO RWY 19L/R) AND THEN CONTINUED APCH (NOW TO RWY 25L). NEAREST APCH WAS APPROX 1 NM TO OTHER ACFT (TURBOPROP COMMUTER). REMAINDER OF APCH TO LNDG ON RWY 25L WAS RELATIVELY UNEVENTFUL CONSIDERING CONFUSION AS TO HOW SIT HAD DEVELOPED. HOW DID IT HAPPEN: CALL IT THE 'CASE OF UNMET EXPECTATIONS.' TOLD TO EXPECT RWY 19L (NOT THE NORMAL RWY AT LAS) CREW WAS FOCUSED ON MAKING GOOD APCH TO UNUSUAL RWY. CREW WAS NOT NOTIFIED OF ATIS CHANGE FOR RWY CHANGE TO LNDG ON RWY 25L; NOR DID APCH INFORM THEM OF CHANGE IN PLANS TO LAND ON RWY 25L. EITHER WOULD HAVE BROKEN CREWS FOCUS ON RWY 19L. CREWED DID ACKNOWLEDGED 'RWY 25L;' BUT HEARD 'RWY 19L' (HEARING WHAT WE EXPECTED TO HEAR). IT WAS OUR FAULT BUT WE WERE ALSO SET UP FOR IT. HOW TO PREVENT: 1) CREWS DON'T FIXATE ON WHAT YOU'RE EXPECTING -- BE ALERT FOR CHANGES. 2) WHEN CHANGING RWY CONFIGNS; MAKE SURE ALL PLANES ON APCH ARE INFORMED. SUPPLEMENTAL INFO FROM ACN 431293: WE WERE LED DOWN THE 'ROSEY' PATH BECAUSE OF ATIS AND APCH TELLING US THAT WE SHOULD EXPECT RWY 19L. HAD APCH TOLD US A NEW ATIS WAS CURRENT; THAT WOULD HAVE BROKEN THE CHAIN. THE NEW ATIS WOULD HAVE TOLD US THAT RWY 25L WAS THE ACTIVE.