A CPR JET PIC OVERSHOT HIS ALT IN DSCNT WHEN SEARCHING FOR ANOTHER APCH PLATE. STL APCH CTLR HAD CHANGED THE IAP TO A REGULAR ILS FROM AN LDA RWY 12 APCH.

Narrative

WE WERE BEING RADAR VECTORED BY STL APCH CTL FOR THE RWY 12L LDA APCH AT STL. APCH BRIEFING HAD BEEN COMPLETED AND WE WERE IN A SERIES OF TURNS AND STEPDOWNS. WX CONDITIONS WERE CHANGING AND I BELIEVED APCH WAS SETTING US UP FOR A SLAM-DUNK BASE TO FINAL. IT HAD BEEN A NICE CALM FLT BUT THINGS WERE STARTING TO HAPPEN FAST. APPROX 7 MI NW OF THE ARPT AT 7000 FT ON A 270 DEG HDG; WE WERE TOLD TO TURN TO A 290 DEG HDG AND DSND TO 6000 FT. SOMEWHERE ABOUT HERE WE WERE TOLD TO REDUCE TO 210 KTS AND DSNDING THROUGH 6400 FT WE WERE TOLD TO CHANGE TO THE RWY 12L ILS APCH! I FELT TIME WAS GETTING REAL SHORT BEFORE THEY WOULD TURN US ON A BASE (TO INTERCEPT THE LOC) AND I WAITED WITH ANXIETY WHILE THE COPLT TRIED TO FIND THE RWY 12L ILS APCH PLATE. MY ATTN WAS DIVERTED TO HELPING HIM FIND THE PROPER APCH AND GETTING IT CLIPPED TO THE YOKE; WHICH I DID CLUMSILY. THEN THE ALT ALERT CHIME RANG AND I LOOKED UP TO FIND US GOING THROUGH 5700 FT! WE DSNDED TO ALMOST 5600 FT BEFORE THE AIRPLANE STARTED BACK UP AND I QUICKLY LEVELED OFF AT 6000 FT WHEN APCH GAVE US ANOTHER SPD REDUCTION AND TURN. APCH MADE NO COMMENT ABOUT OUR ALT. FROM THERE ON IN WE WERE HURRIED GETTING SET UP FOR THE CHANGED APCH AND ONLY HAD TIME TO EACH DO A SELF BRIEF. LOOKING BACK AT THIS EVENT IS QUITE PAINFUL BECAUSE OF THE CONTRIBUTING FACTORS. FROM MY PERSPECTIVE: 1) STL APCH CTL STARTED THE BALL ROLLING BY CHANGING TO A NEW DIFFERENT APCH FOR US WAY TOO LATE AND CLOSE IN FOR OUR POS! WE FELT VERY PRESSURED! IF THEY WOULD HAVE TOLD US THAT WE COULD HAVE EXTRA TIME IF WE NEEDED IT TO SET UP FOR THE APCH; IT COULD HAVE MADE A WORLD OF DIFFERENCE. ON THE OTHER HAND; WE COULD HAVE ASKED FOR OR DEMANDED THE EXTRA TIME. 2) FATIGUE. THIS WAS THE 10TH HR OF A 13 1/2 HR DAY AND I WAS TIRED WITH NO REST THROUGHOUT THE DAY. 3) CRM. WHERE WAS IT? FLY THE AIRPLANE FIRST! I KNEW BETTER AND SHOULD HAVE LET THE COPLT DO HIS JOB AND I MINE. HERE IS WHERE I BELIEVE FATIGUE PLAYED A BIG PART IN SLOWING AND CLOUDING MY JUDGEMENT. 4) AVIONICS. A 300 FT DEV IS A VIOLATION. SO WHY CAN'T AN ALT ALERT CHIME (WHICH GOT MY ATTN) BE SET TO RING AT 100 OR 150 FT DEV? THIS SHOULD BE LOOKED INTO AS A HELPFUL FIX. 5) MAKE BETTER USE OF THE AUTOPLT. WE LIKE TO HAND FLY A LOT OF THE TIME BELOW 15000 FT TO KEEP US SHARP. BUT THERE ARE TIMES THAT USING THE AUTOPLT IS SMARTER AND SAFER!