AN A320 FO RPT ON A CLRNC MISUNDERSTANDING WHILE IN DSCNT ON THE PDZ 3 ARR INTO LAX; CA.

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ZLA CLRED US 'DIRECT KONZL; FLT PLAN RTE (TNP; PDZ 3; LAX) AFTER PASSING TNP VOR.' SUBSEQUENTLY ISSUED CLRNC TO 'CROSS KONZL AT 17000 FT.' ALL WAS FINE UP UNTIL WE PASSED KONZL. ZLA THEN SWITCHED US TO APCH. CAPT HAD BEEN BUSY WITH APCH CHKLIST AND FMS; BUT IMMEDIATELY SWITCHED FREQS. MEANWHILE; I; BELIEVING WE WERE CLRED ON THE PDZ 3 ARR AND FINDING US JUST 4 MI FROM THE NEXT FIX (TRTLE); BEGAN A DSCNT TO COMPLY WITH THE 'CROSS AT 16000 FT' RESTR PUBLISHED ON THE CHART. APCH THEN QUERIED US AS TO OUR ALT; WHICH AT THAT POINT WAS 16400 FT. CAPT REPLIED THAT WE WERE DSNDING ON THE PDZ 3. CTLR STATED THAT WE WERE NEVER CLRED FOR THE PDZ 3; BUT IMMEDIATELY ISSUED SUCH CLRNC. CTLR THEN GAVE US A REVISED RWY; QUICKLY FOLLOWED BY 2 SPD RESTRS. CAPT BECAME IMMERSED IN FMS (NORMAL IN SUCH SIT) AND SLOWING DOWN/GOING DOWN BECAME A PROB. A MISUNDERSTOOD AND AMBIGUOUS CLRNC; COUPLED WITH CTR'S AND APCH'S FAILURE TO PROVIDE TIMELY INSTRUCTIONS CONTRIBUTED. THEY CAN'T REASONABLY EXPECT US TO COMPLY WITH AN ALT RESTR 4 MI FROM THE FIX AT 320 KIAS; WITH CLRNC STILL PENDING. (TOO MANY LAST MIN CHANGES AT LAX. WE ALWAYS MANAGE TO COMPLY; BUT IT'S HARDLY EVER PRETTY!) ADD TO THE MIX A 12 1/2 HR DUTY DAY AND EVEN 2 VERY EXPERIENCED PLTS ARE QUICKLY BURIED!