A320 CREW DSNDS EARLY ON ARR INTO LAX.

Narrative

WE WERE PROCEEDING TO THE CIVET INTXN AND ANTICIPATING THE CIVET ARR TO LAX. THE ARR WAS SELECTED FROM THE DATABASE AND INSERTED INTO THE FLT PLAN; THE XING RESTRS WERE REVIEWED AND THE APCH FOR RWY 25L REVIEWED. PRIOR TO CIVET WE WERE CLRED DIRECT TO SNRKL INTXN WITH A CLRNC TO DSND ON THE MITTS ONE ARR; THE FO INSERTED THE NEW ARR INTO THE FMGC AND CLRED UP THE REMAINDER OF THE FLT PLAN. WE REVIEWED THE XING ALTS AND BRIEFED THE APCH TO RWY 24R. WHEN THE APCH WAS SELECTED FROM THE DATABASE IT WAS INSERTED USING THE 'VIA' FUNCTION FROM THE STAR; WHICH IS NORMAL FOR THAT APCH TO LAX. THE END OF THE STAR AND THE IAF FOR RWY 24R ARE THE DENAY INTXN AT AN ALT OF 8000 FT (AT OR ABOVE). WE WERE GIVEN A FREQ CHANGE AT ABOUT THE SAME TIME WE ARRIVED AT DENAY DSNDING TO 8000 FT. AS THE FO WAS CHKING IN ON THE NEXT FREQ; I WAS LOOKING AT THE APCH PLATE AND THE DISPLAY ON MY NAV DATA SCREEN WHICH HAD THE ALT CONSTRAINTS DISPLAYED FOR THE STAR AND THE APCH. BECAUSE THE A320 IS HARD TO 'SLOW DOWN AND GO DOWN' I WAS A LITTLE CONCERNED WITH MAKING THE NEXT ALT OF 4000 FT IN ABOUT 8 MI. THERE WAS NO DISCONTINUITY BTWN THE STAR AND THE APCH AND I MISTAKENLY SET 4000 FT IN THE FCU AND STARTED A DSCNT. THE FO AND THE CTLR BOTH QUESTIONED OUR ALT AT THE SAME TIME BUT BECAUSE OF OUR RELATIVELY HIGH RATE OF DSCNT; WE WERE ALREADY 500-700 FT LOW. TOO GREAT A RELIANCE ON THE NAV DISPLAY; COUPLED WITH A BUSY APCH ENVIRONMENT AND A FAILURE ON MY PART TO CONFIRM THE ALTS WITH THE OTHER PLT LED TO THIS ALTDEV WHICH FORTUNATELY CAUSED NO CONFLICTS WITH OTHER ACFT. SUPPLEMENTAL INFO FROM ACN 453578: ON DSCNT INTO LAX WE WERE GIVEN A LAST MIN CHANGE TO DSND VIA THE MITTS ARR. WE HAD PREVIOUSLY ANTICIPATED THE CIVET ARR. THE DSCNT WAS ACCOMPLISHED USING SELECTED AIRSPDS AND SELECTED ALTS FLOWN USING THE AUTOPLT. THE CAPT WAS THE PF. OUR CLRNC LIMIT WAS DENAY INTXN AT OR ABOVE 8000 FT; THE LAST FIX ON THE ARR. ATC DID NOT TURN US OVER TO THE APCH CTLR UNTIL WE WERE AT DENAY. DENAY IS ALSO DEPICTED ON THE ILS APCH RWY 24R. THE CAPT MENTIONED HE WAS CONTINUING THE DSCNT TO 4000 FT (THE ACFT WAS IN CONTINUOS DSCNT AND WAS OBVIOUSLY GOING TO BE SLIGHTLY ABOVE 8000 FT AT DENAY). THE CAPT PROBABLY SAW 4000 FT WAS THE ALT SHOWN AT THE NEXT INTXN ON THE APCH PLATE AND WAS ALSO DEPICTED ON THE NAV DISPLAY. AS I WAS DIALING THE NEW FREQ I MENTIONED TO THE CAPT THAT WE ARE NOT CLRED FOR THE APCH. I TRIED TO GET MY CALL INTO ATC QUICKLY SO WE MAY CONTINUE THE DSCNT AND RECEIVE CLRNC TO JOIN THE APCH. AS I CALLED THE CTLR I NOTICED WE WERE AT 7700 FT AND DSNDING. AT THE SAME TIME THE CAPT DISCONNECTED THE AUTOPLT AND ATTEMPTED TO STOP THE DSCNT. THE CTLR QUERIED MY CALL AND REMINDED US THE ARR ENDED AT DENAY AT 8000 FT THEN IMMEDIATELY CLRED US FOR THE APCH. IT WAS OUR RESPONSIBILITY TO FOLLOW THE ASSIGNED CLRNC ALTHOUGH ATC HAD NOT GIVE US CLRNC BEYOND DENAY UNTIL WE WERE AT DENAY; BUT THAT IS NOT UNUSUAL IN A BUSY AREA SUCH AS THIS. FLYING ACFT IS OUR PRIMARY TASK; ATC AND OTHER DUTIES ARE SECONDARY. AS THE PNF I COULD HAVE BEEN MORE PROACTIVE TOWARDS ENSURING THE PF REMAINS FOCUSED TO THE TASK OF FLYING THE ACFT AND ADHERING TO THE CLRNC. A THOROUGH BRIEFING PRIOR TO THE DSCNT PHASE IS GOOD TECHNIQUE; BUT ATC SOMETIMES OPERATES IN A DYNAMIC ENVIRONMENT THAT LAST MIN CHANGES ARE NECESSARY. DURING A BUSY PHASE OF FLT SUCH AS IN A DSCNT; THESE CHANGES CAN LEAD TO INCREASED WORKLOAD AND POTENTIAL FOR ERRORS.