THE ATIS BROADCAST INDICATED ALL ACFT TO EXPECT AN ARR NOT BEING FLOWN. WHILE LOADING NEW ARR INTO THE FMS APCH CTL CLRED ACFT TO REMAIN ON PREVIOUS ARR RTE. DURING EFFORT TO RELOAD ARR ACFT WAS UNABLE TO COMPLY WITH A XING RESTR.

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OUR FLT WAS ON THE PDZ 3 ARR TO LAX VIA THE TNP TRANSITION. WE WERE JUST E OF TNP AT FL350 WHEN WE WERE 'CLRED' FOR THE ARR. ZLA ASKED US TO BEGIN AN EARLY DSCNT FOR THE PLANNED FIRST XING RESTR OVER KONZL AT 17000 FT. I WAS THE PF; AND THE FO WAS PERFORMING THE COMPUTER DATA ENTRY AND ATIS GATHERING CHORES. HE WAS RELATIVELY INEXPERIENCED ON THE A320; HAVING ONLY BEEN ON THE ACFT SINCE SEP/98 AND FLYING HIS FIRST TRIP IN 2 MONTHS. AFTER BEGINNING THE DSCNT; A NEW ATIS WAS RECEIVED INDICATING THAT ALL ACFT COULD EXPECT TO BE CLRED TO LAX VIA THE MUDDE 4 ARR AND ALSO TO EXPECT RWY 25R SIDESTEP TO RWY 25L. (NORMALLY; THE PDZ 3 ASSUMES AN APCH TO RWY 25L.) AS THE FO BEGAN TO TRY TO INSERT THE MUDDE 4 ARR; IT BECAME APPARENT TO US THAT IT WOULD NOT WORK IN CONJUNCTION WITH OUR PREVIOUS ROUTING. (PDZ 3 USES PDZ VOR; THE MUDDE 4 USES LAX.) EACH SUCCEEDING ATTEMPT TO INSERT A NEW ARR BASICALLY WAS 'CLRING' THE PREVIOUSLY INSERTED XING RESTRS AND THE VERT PATH CALCULATIONS HAD TO BE REDONE BY THE FMGC. FINALLY; WE QUERIED ZLA AS TO THE ARR ROUTING TO EXPECT; AND WERE TOLD TO PLAN ON THE PDZ 3. BY THIS TIME; I HAD BEEN DIVIDING MY ATTN FOR SO LONG BTWN FLYING THE ACFT AND HELPING THE FO WITH THE COMPUTER ENTRIES; THAT WE WERE GOING TO BE ABOUT 700 FT HIGH OVER KONZL. SEEING THAT; I IMMEDIATELY SELECTED 'OPEN DSCNT' AND INCREASED OUR AIRSPD BY 20 KTS. (THE ALT WINDOW STILL DISPLAYED THE 8000 FT XING ALT FOR FUELR THAT I HAD PREVIOUSLY SELECTED TO COMPLY WITH THE PDZ 3 ARR.) THE VERT PATH WAS INTERCEPTED AGAIN OVER KONZL AT 17000 FT AND I RE-ENGAGED MANAGED VERT DSCNT TO MAKE THE 16000 FT XING AT TRTLE; NOTING THE APPROPRIATE 'ENGAGED' INDICATION ON THE FMA. THE ACFT WAS PROBABLY DSNDING AT ABOUT 3200 FPM WHEN 'MANAGED DSCNT' WAS ENGAGED; AND ZLA WAS DIRECTING US TO SLOW TO 280 KTS; SO I EXTENDED THE SPD BRAKES AND SELECTED 280 KTS ON THE FMS CTL PANEL. AS I LOOKED AT THE PFD AGAIN TO CHK OUR POS ON THE VERT PATH; WE WERE APCHING 15700 FT ABOUT 3 NM E OF TRTLE -- OBVIOUSLY BELOW THE PATH. I IMMEDIATELY DIALED IN 16000 FT AND SELECTED 'OPEN CLB;' SEEING THE ACFT SAG TO ABOUT 15600 FT BEFORE STARTING ITS CLB BACK TO 16000 FT. WE MANAGED TO CROSS TRTLE WITHIN 100 FT OR SO OF THE RESTR; AND PROCEEDED ON TO A LNDG AT LAX WITH NO COMMENT FROM CTR. WITHOUT A DOUBT; THE PRIMARY RESPONSIBILITY FOR THE FAILURE TO OBSERVE THE XING RESTR AT TRTLE RESTS WITH ME. AS THE PF AND AS THE CAPT; I AM RESPONSIBLE TO ENSURE THAT WE COMPLY WITH THE CLRNC; REGARDLESS OF DISTRS. AN ARR TO LAX IS SELDOM A ROUTINE EVENT; IN MY EXPERIENCE. THERE ARE USUALLY ADDITIONAL REQUESTS BY ATC TO ADHERE TO ALT OR AIRSPD RESTRS THAT ARE NOT PART OF THE STAR AND WHICH (UNFORTUNATELY) USUALLY ARE ASSIGNED AFTER THE DSCNT HAS BEGUN; LIMITING OUR ABILITY TO COMPLY. FOR ALL OF THE WORKLOAD 'REDUCTIONS' THAT THESE FMS-EFIS EQUIPPED ACFT PROMISE; THOSE ASSETS CAN QUICKLY BECOME 'LIABILITIES' WHEN OUR ATTEMPT CHANGES TO YOUR ROUTING OR RWY IN THE MIDDLE OF THE APCH. IF YOU ARE EXPERIENCED AND NIMBLE ENOUGH; YOU CAN DEAL WITH THESE 'MODIFICATIONS' WITH LITTLE DIFFICULTY. ALSO; SOME ARR/RWY COMBINATIONS CAN EASILY BE CHANGED BY SELECTING THE APPROPRIATE 'VIAS' TO STRING THE INTERVENING WAYPOINTS/XING RESTRS AHEAD OF YOU AUTOMATICALLY. OTHER APCHS; LIKE THIS ONE TO LAX; DO NOT AUTOMATICALLY 'STRING' ALL OF THE WAYPOINTS AHEAD OF YOU. AS A RESULT; EACH TIME WE ATTEMPTED TO CHANGE TO OUR ARR/RWY; IT WAS NECESSARY TO MANUALLY INSERT 3 WAYPOINTS AND THE ASSOCIATE XING RESTRS FOR THE APPROPRIATE RWY. THIS IS WAY TOO LABOR INTENSIVE FOR LATE-IN ARR CHANGES; AND REQUIRES TOO MUCH 'HEADS DOWN' FOR A BUSY ARR ARPT LIKE LAX. OUR AIRLINE HAS OUTGROWN THE CAPABILITIES OF THE PRESENT FMGC DATABASE TO STORE ALL THE NAV DATA NEEDED. AS A RESULT; THE COMPANY HAS BEEN 'SELECTIVELY' REDUCING THE AMOUNT OF STORED INFO WE HAVE ACCESS TO AND WE MUST MANUALLY INSERT MORE AND MORE WAYPOINTS IN THE ENRTE AND APCH ENVIRONMENT. I WOULD LIKE TO SEE THE ACFT CERTIFICATION PROCESS CHANGED OR THE ACFT SYS DESIGN MODIFIED TO MAKE IT EASIER TO UPGRADE AVIONICS AS TECHNOLOGY IMPROVES. A LOT OF OUR WORKLOAD COULD BE REDUCED BY HAVING EXPANDED DATABASE MEMORY CAPACITY AND/OR PROCESSOR CAPABILITY. IT COULD ALSO BE REDUCED BY GETTING ATC TO LET US KNOW AS MUCH IN ADVANCE OF OUR DSCNT AS POSSIBLE WHAT SORT OF CHANGES TO THE STAR OR APCH TO EXPECT. WHY WAS THE LAX ATIS ADVERTISING THE MUDDE 4 ARR WHEN THAT WAS NOT THE ONE IN USE? FOR OUR PART IT CREATED ONLY NEEDLESS CONFUSION THAT COULD EASILY HAVE BEEN AVOIDED HAD LAX APCH ONLY COMMUNICATED WITH THE LAX TWR A LITTLE BETTER.