AN A320 FLC IS CONFUSED ABOUT THE ARR AND DSCNT CLRNC WHILE ON THE PDZ 3 STAR INTO LAX; CA.

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FLT FROM PHX TO LAX. ASSIGNED PDZ 3 ARR; CLRED TO CROSS KONZL INTXN AT 17000 FT. AFTER PASSING KONZL; STAR HAS YOU DSND TO 16000 FT AT TRTLE INTXN. SOCAL APCH CTLR CLRED US FOR PDZ.3 ARR FOR RWY 25L. THE FMGC WAS PROGRAMMED FOR RWY 24R. AS PNF; I BEGAN TO MODIFY THE STORED FLT PLAN. THERE WAS CONFUSION WHETHER WE WERE CLRED TO DSND TO 16000 FT BY TRTLE INTXN; BUT THE CAPT AND I WERE HAVING SMALL DIFFICULTY WITH A PROPER REPROGRAMMING OF FMGC. I HAD ENTERED 1 TOO MANY WAYPOINTS AND THE CAPT WAS POINTING THAT OUT TO ME. STILL LEVEL AT 17000 FT AND APCHING TRTLE INTXN; I QUESTIONED ATC IF WE WERE CLRED TO DSND VIA THE PDZ.3 ARR. WE WERE .3 DME FROM TRTLE; BUT NOT AT 16000 FT MSL. I STATED WE WOULD NOT MAKE TRTLE IF WE WERE CLRED. THE ATC CTLR SAID NO PROB; 'DSND YOUR DISCRETION' (14000 FT; WHICH IS THE NEXT FIX). WE COMPLIED AND EXECUTED THE ENTIRE APCH WITHOUT FURTHER INCIDENT. LESSONS LEARNED: 1) ALWAYS VERIFY IF A DSCNT IS REQUIRED TO EXECUTE DSCNT. 2) MAKE SURE 1 PLT IF FLYING THE ACFT. 3) SUGGEST CTLR USE PHRASE 'DSND VIA' WHEN AUTOMATIC STEPDOWNS ARE BUILT INTO ARR (AS IN OLYMPIA.2 ARR -- SEATAC). 4) XCHK WHEN A SID/STAR SAYS 'EXPECT' VERSUS 'CROSS AT.' THERE IS A BIG DIFFERENCE.