LGT ACFT ON STAR ARR AND DSNDING TO CAPTURE GS. RPTR FO; PNF; WAS INSTRUCTED BY CAPT TO RESET ALT ABOVE ACFT SO HE COULD CONTINUE IN 'OPEN DSCNT' TO CAPTURE GS; BUT THE FMA REVERTED TO VERT SPD. CAPT WANTED OPEN DSCNT SO WHEN RPTR SET IT THE ACFT REVERTED TO OPEN CLB; PWR INCREASING FOR CLB AND SPD INCREASED; OVERSPEEDING THE FLAP SETTING.

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CAPT WAS HAND FLYING; AUTOTHRUST 'ON.' WHILE STEPPING DOWN ON THE CIVIT 4 ARR AT LAX AND TRANSITIONING TO THE ILS FROM ABOVE THE GS WE EXPERIENCED A FLAP OVERSPD. WITH 5000 FT SET IN THE ALT WINDOW AND IN 'OPEN DSCNT;' SLOWING AS ASSIGNED BY ATC AND DSNDING TO CAPTURE THE GS; THE PF TOLD ME TO SET THE ALT ABOVE OUR PRESENT ALT (SO THE ACFT WOULD CONTINUE DSNDING PAST 5000 FT TO CAPTURE THE GS). I DID THIS AND THE FMA REVERTED TO VERT SPD. I TOLD THE CAPT I'D GIVE HIM 1000 FT VERT SPD DOWN TO CAPTURE THE GS; THIS WAY THE FLT DIRECTOR WOULD MATCH WHAT WE WERE DOING. HE SAID HE DIDN'T LIKE THAT MODE; AND TO GIVE HIM OPEN DSCNT INSTEAD; SO I PULLED THE ALT KNOB TO DO SO; FORGETTING THAT I HAD SPUN THE ALT KNOB UP TO SOMETHING ABOVE OUR PRESENT ALT; AND NOT CHKING THE FMA AFTER DOING SO. IF I HAD CHKED THE FMA; I WOULD HAVE SEEN 'OPEN CLB.' THIS CAUSED THE ENGS TO SPOOL UP TOWARDS CLB PWR; RAPIDLY ACCELERATING US TO VFE +10 KTS. CONTRIBUTING TO THIS WAS OUR ENTRY INTO A CLOUD BUILDUP; FURTHER INCREASING OUR AIRSPD. ALSO; THE THROTTLES ON THIS ACFT DON'T MOVE IN THE AUTOTHROTTLE MODE (ONE LESS CLUE AS TO ENG THRUST TRENDS). THIS COULD BE PREVENTED BY 1) CONTINUING TO STEP THE ALT DOWN UNTIL GS CAPTURE; 2) NEVER TOUCHING THE FLT CTL UNIT UNTIL TOLD TO DO SO BY THE PF; 3) ALWAYS CHKING THE FMA'S (FLT MODE ANNUNCIATOR) AFTER AN FCU INPUT.