LGT OVERSHOOTS ASSIGNED ALT DURING DESCENT.

Narrative

ON INITIAL DSCNT FROM FL330 TO FL310; A DISTR IN THE FORM OF A MINOR SYS PROB FOCUSED ATTN AWAY FROM THE FRONT PANEL. DURING THE DISCUSSION; THE 1ST ALT ALERT WENT UNNOTICED BY THE PLTS. AUTOPLT CONTINUED DSCNT THROUGH FL310 UNTIL AT APPROX 250' LOW; THE ALT ALERT SOUNDED AND THE RECOVERY WAS INITIATED IMMEDIATELY WITH MAX ERROR OF APPROX 500'. MOMENTS LATER; CLRNC WAS RECEIVED TO CONTINUE DSCNT WITH NO UNUSUAL COMMENTS. FACTORS INVOLVED IN THIS ERROR WERE A FAILURE OF THE PLT FLYING TO REMAIN EXCLUSIVELY THE MASTER OF THE ACFT AND REMOVE HIMSELF FROM NON FLYING DUTIES; A FAILURE OF PLT NON FLYING TO CROSS CHK PLT FLYING; AN OVERRELIANCE IN THE FORM OF 'KNEE JERK' RESPONSE ON AUTOMATED SYS AND REMINDERS. REFLECTION ON THIS MISTAKE HAS MOTIVATED ME TOWARDS IMPROVED AWARENESS AND ATTN TO DETAIL. ALSO; THOUGHTS ON HOW TO REDUCE THE MAX ERROR WHEN THIS OCCURRENCE INEVITABLY HAPPENS ARE POSSIBLE IMPROVEMENTS OF THE ALT ALERT SYS. 1) NARROW THE ALERT ENVELOPE FROM PLUS/MINUS APPROX 250' TO PLUS/MINUS APPROX 175'. THIS SHOULD ALERT THE PLTS SOONER TO A DEV. 2) INTEGRATE VERT SPD LOGIC INTO THE SYS SUCH THAT WHEN PASSING THE PROGRAMMED ALT WITH VERT SPD IN EXCESS OF 500'/MIN; THE ALERT WILL SOUND OFF. I HOPE THESE SUGGESTIONS MIGHT BE CONSIDERED BECAUSE THE HUMAN FACTOR WILL ALWAYS BE PRESENT; THEREFORE; THE SOONER SUCH ERRORS ARE DETECTED; THE SOONER THEY CAN BE CORRECTED.