AN A320 CREW CROSSED A LAS STANDARD ARR RTE AT A HIGHER ALT CONSTRAINT HIGH.

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WITH FO FLYING; WE CHKED IN WITH LAS APCH CTL AND WERE GIVEN A CLRNC TO CROSS CLARR INTXN AT 13000 FT; DELETE THE SPD; AND CLRED TO DSND VIA THE KEPEC ARR. THE FO SET SELECTED SPD AT 300 KIAS BUT NO LOWER ALT IN THE FCU. I DID NOT QUESTION THAT BECAUSE WE HAD 30 NM TO LOSE 1000 FT; THE NEXT ALT RESTR AT KEPEC. WHILE WHAT I DID NOT REALIZE IS THAT MY FO DID NOT CATCH THE DSND VIA CLRNC AND WE STARTED THE TURN FOR KEPEC WE WERE STILL AT 13000 FT. A 300 KTS OPEN DSCNT WAS INITIATED BUT WE STILL PASSED OVER KEPEC ABOVE THE REQUIRED 12000 FT. WE DID MAKE THE NEXT ALT AT IPUMY AT 11000 FT. AT THAT POINT; THE LAS APCH CTLR HANDED US OFF TO THE NEXT CTLR WITHOUT ANY COMMENTS. THE NEW CTLR DID NOT HAVE ANY COMMENTS FOR US EITHER. IT ALL HAPPENED SO FAST THAT WE HAD THE SIT CORRECTED BEFORE WE COULD SAY ANYTHING TO APCH ABOUT IT. AS FAR AS WE KNOW; THERE WAS NO TFC CONFLICTS AND COMPLETED A VISUAL APCH TO LNDG. IT IS IMPERATIVE THAT BOTH PLTS UNDERSTAND THE CURRENT CLRNC. THE NEXT ALT FCU XCHK IS THE FIRST CHK THAT THIS IS SO. THE DAY BEFORE ON THIS SAME ARR OUR CLRNC WAS TO MAINTAIN 13000 FT AND NOT TO DSND VIA THE ARR. THE FO SAID HE ANTICIPATED THAT CLRNC AND NEVER REGISTERED THE DSCNT VIA CLRNC THIS DAY. I SHOULD HAVE INSURED THAT THE LOWEST ALT WAS SET IN THE FCU FOR THE VIA CLRNC AND; IF NOT MANAGED AT THAT TIME (WHICH FROM PRIOR EXPERIENCE WOULD HAVE STARTED A 200 FPM DSCNT TO 12000 FT) ENSURED THAT IT WAS MANAGED FOR THE DSCNT IN TIME TO CROSS KEPEC AT 12000 FT. SETTING THE NEXT CLRED ALT WOULD HAVE BROUGHT THE FO BACK INTO THE LOOP AS WELL.