ACR MLG OVERSHOT ALT ON CLIMB.

Narrative

I WAS CAPT OF A MLG FLT FROM ORD TO STL. WE WERE APPROX 35 MI N OF THE ROBERTS VOR WHEN WE WERE CLRED TO CLB TO 22000'. THE DFGS (DIGITAL FLT GUIDANCE SYS) WAS SET UP ON AUTOPLT WITH EPR LIMIT (CLB PWR) AND IAS HOLD. WE WERE CLBING THROUGH 21000' AS WE WERE APCHING THE ROBERTS VOR. THE F/O CALLED 1000' TO GO AND WE BOTH NOTED THE ALT ARM LIGHT ON. I TURNED TO LOOK AT MY ARR PAGE TO STL; TO CHK THE OUTBND FROM THE VOR. AS I LOOKED BACK TO THE PANEL; I NOTICED THE ACFT WAS CLBING THROUGH 22000' THE ALT ARM LIGHT WAS OFF AND THE ALT CAP LIGHT WAS NOT ON. I DISCONNECTED THE AUTOPLT; PUSHED THE NOSE OVER;AND THE ALT TOPPED OUT AT 22400'. THE PUSHOVER WAS MADE MORE DIFFICULT BECAUSE THE THROTTLES REMAINED IN EPR LIMIT WITH CLB PWR SELECTED. I HAVE BEEN A CAPT ON THE MLG FOR THREE YEARS AND HAVE BEEN VERY MUCH AWARE OF THIS PROB. IT DISTURBS ME THAT A SYS THAT IS SUPPOSED TO HELP THE WORKLOAD IN A TWO MAN COCKPIT IS ALSO A TRAP WAITING TO CREATE A VIOLATION FOR THAT CREW. I DO NOT UNDERSTAND WHY WE NEED TO SELECT AN ALT AND ARM AN ALT. I AM NOT AWARE OF ANY CONDITION WHERE I WOULD LIKE TO LEVEL AT AN ALT THAT IS NOT SELECTED. FURTHERMORE; IT DOES NOT MAKE ANY SENSE TO ME THAT A 'FLT GUIDANCE SYS' WOULD BE DESIGNED TO CLB OR DSND THROUGH A SELECTED ALT; ARMED OR NOT ARMED. I WILL CONTINUE TO BE DILIGENT WITH THE MLG DFGS; BUT THE NEED TO FOCUS SO MUCH ATTN ON A POSSIBLE ALT 'BUST' IS A SET-UP TO MISS SOME OTHER IMPORTANT EVENT. I ALSO LEARNED; FROM THIS EXPERIENCE; NOT TO DISCONNECT THE AUTOPLT AND PUSHOVER. NEXT TIME (HOPEFULLY; THERE WON'T BE ANY) I WILL REACH OVER AND SELECT ALT HOLD. AFTER THE ACFT LEVELS OFF; I WILL ROLL THE VERTICAL SPD SELECT KNOB TO DSND TO THE ASSIGNED ALT. PLEASE HELP US MLG PLTS ESCAPE FROM THIS DESIGN TRAP. THIS IS NOT THE FIRST TIME THAT THE ALT ARM LIGHT HAS GONE OUT ON ME WITHOUT A CREW ACTION.