XING RESTR NOT MET NEAR LAS; NV. CREW COMPLAINS OF FLT MGMNT SYS DESIGN.

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THIS HAPPENED ON THE ARR TO LAS VEGAS THAT I HAVE FLOWN MANY TIMES BEFORE. THE XING RESTR WAS INSERTED IN THE FMC. THE FO WAS FLYING. I LEFT THE ATC FREQ TO GET THE ATIS WHILE WE WERE STILL AT CRUISE ALT. WHILE STILL OFF I INFORMED THE FO OF THE RWY IN USE. HE INSERTED THE NEW RWY IN THE FMC. SOON THEREAFTER HE RECEIVED THE ANTICIPATED XING RESTR AND STARTED TO DSND NOT REALIZING THAT THE XING RESTR HAD DROPPED OUT OF THE FMC. THE FMC VERT DSCNT PATH WOULD NOW BE ABOUT 2000 FT HIGH. ABOUT THIS TIME I CAME BACK FROM GETTING THE ATIS; GATE ASSIGNMENT; ETC. I QUICKLY SAW WE WERE HIGH; BROUGHT IT TO HIS ATTN; AND TOLD HIM TO DSND AS QUICKLY AS POSSIBLE. I BELIEVE WE WERE ABOUT 600 FT HIGH XING THE FIX. WHILE WE THE PLTS ARE RESPONSIBLE TO MEET THESE RESTRS AND GREATER SITUATIONAL AWARENESS IS DUE ON MY PART WHEN I AM OFF FREQ; IT MUST BE RECOGNIZED THAT AN FMC THAT DELETES A XING RESTR WHEN A NEW RWY IS INSERTED IS A POOR DESIGN. IT IS WORKING AGAINST THE PLT NOT FOR HIM. AIRBUS REALLY SHOULD CHANGE THIS FEATURE.