A FALCON 20 CAPT; PNF; RPTED AN ALT OVERSHOOT DURING APCH TO GFK.

Narrative

MY COPLT AND I WERE FLYING FROM TVF IN A FALCON 20. AS WE APCHED TVF; I DETERMINED THAT THE WX WAS BELOW MINIMUMS FOR THE APCH BUT ACCEPTABLE AT OUR WX ALTERNATE (900 FT OVCST AND 3/4 NM VISIBILITY). I CONTACTED ZMP TO REQUEST CLRNC TO OUR ALTERNATE OF GFK. AT THIS TIME WE WERE AT 10000 FT MSL; CLRED TO GFK AND GIVEN PLT'S DISCRETION TO 6000 FT MSL. WE TURNED DIRECT TO OUR NEW DEST (ONLY 75 NM AHEAD) AND BEGAN A SLOW DSCNT TO 6000 FT. ONCE ESTABLISHED ON THE NEW HDG; I BRIEFED MY COPLT (PF FOR THIS LEG) ON OUR PLANNED APCH; WX CONDITIONS AT GFK; AND MISSED APCH PROCS. WE WERE IMC FROM ABOUT 12000 FT MSL DOWN; WITH LIGHT TO MODERATE ICING. AT 6000 FT MSL; WE WERE HANDED OFF TO GFK APCH CTL AND GIVEN A PLT'S DISCRETION TO 2600 FT MSL. THE APCH PLATE SHOWED AN MSA OF 2700 FT MSL; SO I RECONFIRMED THE ALT WITH GFK APCH. THEY CONFIRMED OUR CLRNC TO 2600 FT MSL. WE WERE 25 NM FROM THE ARPT ON A VECTOR TO INTERCEPT AN OUTBOUND LEG (DOWNWIND) FOR THE APCH TO ILS RWY 35L. I INFORMED MY COPLT OF THE MSA AND TOLD HIM TO BEGIN A SLOW DSCNT TO 3000 FT AND HOLD THAT ALT UNTIL ESTABLISHED ON THE ILS. AT APPROX 3500 FT MSL; APCH INFORMED US OF A NEW ATIS AND I ADVISED THEM THAT I WOULD PICK IT UP. I BELIEVE THIS WAS MY MISTAKE; BECAUSE I THEN PUT MY HEAD DOWN TO TUNE THE ATIS FREQ AND TO WRITE DOWN THE NEW WX. DURING THIS SHORT TIME; MY COPLT CONTINUED HIS DSCNT THROUGH 3000 FT MSL; PAST THE ASSIGNED ALT (SET IN THE ALERTER) OF 2600 FT MSL AND DOWN TO 2200 FT MSL. PASSING THROUGH -200 FT; THE ALERTER SOUNDED OFF. AT THAT MOMENT; I LOOKED UP TO SEE OUR NEW ALT AND DSCNT RATE AND FIRMLY ANNOUNCED OUR ALTDEV AND ASSIGNED ALT. BY THE TIME THE DSCNT WAS ARRESTED AND A CLB ESTABLISHED; WE HAD DSNDED 400 FT BELOW OUR ASSIGNED ALT AND 500 FT BELOW THE PUBLISHED MSA. I BELIEVE MY FIRST MISTAKE WAS TO TAKE MY ATTN AWAY FROM THE APCH SEQUENCE. AT THIS CRITICAL PHASE OF FLT; I SHOULD HAVE REQUESTED THE CTLR TO UPDATE ME ON THE NEW ATIS. SECONDLY; EVEN THOUGH MY COPLT HAD MORE THAN 500 HRS IN THAT ACFT AND OVER 2000 TOTAL HRS AND SHOULD HAVE BEEN CAPABLE OF MAINTAINING AN ASSIGNED ALT; I SHOULD HAVE MAINTAINED A HIGHER LEVEL OF SITUATIONAL AWARENESS IN THAT PHASE OF FLT AND WX CONDITIONS.