ALT EXCURSION BY THE FO OF AN A319 PASSING KONZL INTXN ON THE PDZ 4 ARR INTO LAX; CA.

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INBOUND LAX ON THE PDZ 4; FO'S LEG. LEVELING 17000 FT OVER KONZL; ZLA CLRED US TO RWY 24R VIA THE PDZ 4. WHILE I WAS ENTERING THE DATA; THE CTR CLRED US TO DSND VIA THE PDZ 4. TRTLE IS 6 MI AWAY; CROSS BTWN 16000 FT AND 17000 FT. FO MISTAKENLY ENTERED 15000 FT IN ALT SELECTOR. CAUGHT HIS MISTAKE AND ENTERED 16000 FT. ALT ALERTER WENT OFF; WHICH WAS THE FIRST I KNEW ABOUT IT BECAUSE I WAS HEADS DOWN; AS WE WERE UNDER 16000 FT AND DSNDING. WE BOTTOMED OUT AT ABOUT 15100 FT AS HE WAS CORRECTING BACK. THERE WAS NO EVENT. THERE ARE NUMEROUS REASONS WHY THIS HAPPENED AND WHY IT SHOULD NOT HAVE HAPPENED. YOU KNOW THEM AS WELL AS I. WHAT YOU MAY NOT KNOW IS THAT THE CTLRS THAT HANDLE INBOUND LAX TFC FREQUENTLY CHANGE ARRS AND RWYS. ALL HAVE NUMEROUS ALT RESTRS AND WHEN THEY DO THIS; THE WORKLOAD ON AN AUTOMATED ACFT SKYROCKETS. LAX CAN BE THE MOST INTENSE OF THE WEST COAST ARPTS TO GET INTO. TO MAKE IT WORSE; THE ALT RESTRS ON ILS FINAL DO NOT ALIGN WITH THE ELECTRONIC GS; SO WE CAN'T JUST FOLLOW THE GS DOWN AND MAKE THEM ALL. IT ALL COMES UP VERY FAST AND IS A POOR SIT. SUPPLEMENTAL INFO FROM ACN 612928: ATC SLOWED ME DOWN AND HELD ME HIGH ON THE PROFILE SO I WENT OPEN DSCNT AND INCREASED THE SPD SLIGHTLY TO MAKE THE XING. ON THIS DSCNT; ATC CLRED US TO LOS ANGELES FOR ILS RWY 24R TO DSND VIA THE PDZ 4. WE HAD ILS RWY 25L PROGRAMMED IN THE FMS SO THE CAPT WAS NOW OUT OF THE LOOP CHANGING THE RWY. ADDITIONALLY; THE 'ACTIVATE' PROMPT ON THE FLT PLAN DISAPPEARED; FORCING HIM TO REPROGRAM THE REGULAR FLT PLAN ON WHICH I WAS NAVING. THAT TOOK HIM ABOUT 30 SECONDS TO FINISH. ALL THIS OCCURRED AT A CRITICAL POINT AND I WAS DISTR; LOSING SITUATIONAL AWARENESS AT KONZL INTXN AS I THEN DSNDED FOR THE NEXT INTXN; TRTLE. REASONS: 1) DISTR DUE TO RWY CHANGE. SEVERAL TIMES I GLANCED TO SEE WHAT THE PLT MONITORING WAS DOING; ESPECIALLY WHEN HE SAID THE FLT PLAN WITH THE NEW RWY COULD NOT BE ACTIVATED. 2) FATIGUE -- IT WAS EVENING ON MY BODY AND I HAD BEEN UP EARLY THAT MORNING TO COMMUTE TO WORK FOR A LATE AFTERNOON TRIP THAT PASSED THROUGH ZZZ BEFORE GOING TO LAX. PREVENTION: 1) STRICT CREW AND ALT AWARENESS. I AM METICULOUS ABOUT OUR PROCS BUT FOUND WITH THIS CAPT OUT OF THE LOOP AND ME DISTR; I MADE THE ERROR. 2) AUTOMATION -- I WAS FORCED OUT OF MANAGED DSCNT BECAUSE OF AIRSPD CHANGE REQUIRED BY ATC PRIOR TO KONZL INTXN. 3) WAIT TO DSND UNTIL PLT BACK IN LOOP; BUT TIGHT WINDOWS ON ALT RESTRS SO WE ARE FORCED TO DSND AGGRESSIVELY AT TIMES.