ALTDEV ALT OVERSHOT IN DSCNT DURING APCH PROC.

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CLRNC TO MAINTAIN 2600 FT AND HDG TO INTERCEPT 1L LOC. FO FLYING AND HIGH. INSTRUCTED FO TO LOWER GEAR AND USE SPD BRAKES TO GET DOWN AND SET UP EARLY FOR APCH. AFTER INTERCEPT; FO DSNDED TO 2000 FT (STILL BELOW GS). I INSTRUCTED HIM TO LEVEL AT 2000 FT AND STAY THERE UNTIL INTERCEPTING THE GS. THIS ALT ACTIVATED A 'LOW ALT ALERT.' ADVISED TWR OF SITUATION AND CONTINUED NORMAL APCH AND LNDG. FO WAS NEW AND RETURNING FROM OVER 80 DAYS OFF OCCUPATIONAL INJURY. HE NEEDED 3 LNDGS AND REFRESHER. CAPT/LINE CHK AIRMAN BACK FROM 3 WK VACATION. BOTH OF US WERE ALERT; BUT RUSTY. IT WAS A BUSY APCH AND THERE WERE SEVERAL DISTRS WHICH CONTRIBUTED TO DSCNT BELOW 2000 FT; HOWEVER; I AM FAMILIAR WITH MC AND FELT IT MADE MORE SENSE TO STAY AT 2000 FT RATHER THAN OVERLOAD THE FO MORE WITH A CLB BACK TO 2600 FT. IN RETROSPECT IT WOULD HAVE MADE MORE SENSE FOR ME TO FLY THE FIRST LEG (WHICH I SUGGESTED); BUT SINCE WE WERE ONLY GOING TO HAVE 4 LEGS AND THE FO SEEMED VERY CONFIDENT I ACQUIESCED. MORE SUBTLE; BUT PROBABLY A FACTOR WAS THE URGE TO ACCOMPLISH THE MISSION WITHIN THE 4 LEG CONSTRAINT. WITH THE EXCEPTION OF THIS LAPSE THE FO WAS VERY CAPABLE.