A B757 ACR FLC CLBS ABOVE THEIR ASSIGNED ALT WHEN THEY ARE OVERWHELMED BY THE AUTOMATION WORKLOAD INVOLVED IN A LOW ALT LEVELOFF WHILE CHANGING THE ACFT'S CONFIGN AND MAINTAINING ITS SPD; WITHIN ITS CONFIGN-BASED; LIMITATIONS.

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THE PROB AROSE ON DEP FROM LAX. OUR CLRNC CALLED FOR A DEP HDG OF 250 DEGS AND A CLB TO 2000 FT. AFTER RAISING THE GEAR AND MAKING THE INITIAL PITCH REDUCTION I REDUCED THE THRUST TO THE CLB SETTING AND STARTED RAISING THE FLAPS. 2000 FT ARRIVES VERY QUICKLY ON THIS DEP SO AS WE CLBED THROUGH ABOUT 1500 FT I REDUCED THE PITCH EVEN MORE SO AS TO NOT OVERSHOOT THE ALT. SHORTLY THEREAFTER I REALIZED THAT THE AIRSPD WAS BUILDING RAPIDLY AND WAS IN FACT ABOUT TO EXCEED THE FLAPS EXTEND SPD. THE FLAPS HAD ALREADY BEEN SELECTED TO THE UP POS BUT WERE STILL IN THE PROCESS OF MOVING UP; SO; TO NOT EXCEED FLAPS EXTEND SPD I DID WHAT I NORMALLY DO -- I INCREASED THE PITCH. BUT IN DOING SO I COMPLETELY FORGOT ABOUT MY PROXIMITY TO 2000 FT. THE FO YELLED A WARNING AS WE WENT THROUGH 2000 FT AND I PULLED THE THRUST TO IDLE AND PITCHED OVER TO REGAIN 2000 FT. THE HIGHEST ALT I SAW WAS ABOUT 2350 FT. HOW DID THIS HAPPEN? WELL; THIS IS A GLASS COCKPIT ACFT AND THIS IS ANOTHER EXAMPLE OF THE CONFLICT BTWN REQUIRED MANEUVERS AND SOPS IN SUCH ACFT. IN THIS CASE THE MANEUVER TO LEVEL AT 2000 FT AND THE SOP TO FLY THE ACFT USING AUTOMATION SUCH AS AUTOTHROTTLES. THE AUTOTHROTTLES WOULD HAVE REDUCED THRUST TO MAINTAIN THE AIRSPD HAD THE AUTO FLT SYS CAPTURED THE ALT; BUT SINCE I HAD DECREASED THE PITCH SOMEWHAT SO AS TO NOT APCH 2000 FT TOO RAPIDLY THE SYS DELAYED THE ALT CAPTURE WHICH IN TURN LEFT THE THROTTLES IN THE CLB THRUST MODE WHICH IN TURN FORCED THE AIRSPD TO BUILD RAPIDLY. CONTRIBUTING FACTORS INCLUDE THE ALT ASSIGNMENT OF 2000 FT. ALL HIGH PERFORMANCE ACFT SHOULD HAVE AN INITIAL ALT ASSIGNMENT OF AT LEAST 5000 FT ABOVE THE ARPT OR HIGHER. ANOTHER FACTOR IS THE DISTR OF THE FREQ CHANGE AND RADIO CALLS REQUIRED AT THIS STAGE OF FLT.