MD80 CREW HAD ALT OVERSHOOT.

Narrative

CAPT WAS FLYING ACFT ON AUTOPLT; DSNDING TO FL240. I WAS ATTEMPTING TO OBTAIN ATIS LNDG INFO FOR CMH. AS I WAS ATTEMPTING TO COPY INFO; I HEARD 'ALT' WARNING GO OFF. I LOOKED UP AND SAW THE ACFT DSNDING THROUGH FL238. I CALLED OUR ALTDEV AND CAPT RETURNED TO FL240. THE PROB WAS PROBABLY CAUSED BY THE FOLLOWING CONTRIBUTING FACTORS: 1) THE MD80 HAS ONLY A SMALL YELLOW WARNING LIGHT ON ALTIMETER TO WARN PLT THAT HE IS APCHING LEVELOFF ALT. IT GOES OUT 250 FT FROM SELECTED ALT AND CAN ONLY BE SEEN IF LOOKING DIRECTLY AT INST PANEL. 2) THE ALT SELECT FEATURE OF FLT GUIDANCE SYS IS EASILY DISCONNECTED BY USE OF THE VERT SPD FUNCTION. 3) ACARS WAS NOT WORKING PROPERLY AND I COULD NOT OBTAIN CMH ATIS FROM IT. 4) CMH VOICE ATIS IS THE SAME FREQ AS GRR APCH CTL. APCH CTL WAS VERY BUSY AND CONSTANTLY INTERFERING WITH ATIS XMISSION; CAUSING EXTREME DISTR FOR PNF. 5) CREW WAS NEARING END OF 13 HR DUTY DAY. CORRECTION FOR PROB: 1) MODIFY MD80 ALT WARNING SYS TO INCLUDE VOICE WARNING APCHING SELECTED ALT. 2) MODIFY FLT GUIDANCE SYS TO BE LESS INFLUENCED BY USE OF VERT SPD CTL WHEN APCHING SELECTED ALT. 3) CHANGE FREQ OF CMH ATIS. NOTE: THIS SEEMS TO BE A VERY COMMON PROB ON THE EAST COAST. 4) BOTH PLTS SHOULD HAVE AVOIDED DISTRS APCHING ALT. 5) COMPANY SHOULD LOOK AT DUTY DAY PROBS. COMING FROM A MIL BACKGND; I FEEL THAT THE MIL WAS LIGHT YRS AHEAD OF AIRLINES WHEN IT COMES TO DEALING WITH HUMAN FACTORS PROBS.