THE AUTOPLT OF A BE58 DID NOT CAPTURE THE SELECTED ALT.

Narrative

WHILE DEPARTING FLAGSTAFF; AZ; ON AN IFR FLT PLAN TO SANTA FE; NM; I INADVERTENTLY CLBED PAST THE ALT CLRNC OF 11000 FT MSL. I WAS ON COURSE FROM FLG TO INW (V291) IN THE GPS-EQUIPPED BE58. AT THE TIME; THE AUTOPLT WAS ON AND 11000 FT WAS SELECTED IN THE BENDIX-KING KFC225 AUTOPLT. THE CLRNC DEV WAS FIRST NOTED WHEN ZAB QUERIED US TO STATE OUR DESIRED FINAL ALT. AT THE TIME; I REPLIED '11000 FT' AND NOTED A CLB ON THE ALTIMETER THROUGH 11800 FT MSL. I TOOK IMMEDIATE ACTION BY DISENGAGING THE AUTOPLT AND RETURNING THE ACFT TO 11800 FT MSL. AFTER TAKING CORRECTIVE ACTION; I APOLOGIZED TO ZAB AND COMPLETED THE REMAINDER OF THE FLT WITHOUT INCIDENT. THERE HAVE BEEN NO KNOWN ISSUES WITH THE AUTOPLT BEFORE OR SINCE THE INCIDENT. THE REASON FOR THE DEV WAS THE FAILURE OF THE CREW TO MONITOR THE AUTOPLT'S CAPTURE OF THE PROGRAMMED ALT. THE CREW (MYSELF) WAS DISTR WITH THE ACFT PERFORMANCE INSTS WHILE ATTEMPTING TO MAINTAIN A MAX PERFORMANCE CLB IN NIGHT CONDITIONS IN MOUNTAINOUS TERRAIN. WHEN THE DEV WAS NOTED; THE ALT-PRESELECT-EQUIPPED AUTOPLT DID HAVE 11000 FT PROGRAMMED IN AND IT WAS 'ARMED' TO CAPTURE. WHY IT DID NOT CAPTURE IS UNCLR; BUT IT IS CLR THAT I AM AT FAULT FOR ALLOWING THE DEV TO PROGRESS TO THE POINT OF ATC INQUIRY REGARDING THE ACFT'S ALT. AFTER THE DEV; THE AUTOPLT PERFORMED FLAWLESSLY THE REMAINDER OF THE FLT; WHILE BEING CLOSELY MONITORED. THIS CONCURRENCE HAS REMINDED ME TO REMAIN VIGILANT OF ASSIGNED ALTS AND MONITOR AUTOPLT OPS MORE CLOSELY. OUR COMPANY POLICY CALLS FOR CREW MEMBERS TO CALL '1000 FT TO GO' PRIOR TO ASSIGNED ALTS. IT IS ALSO MY PERSONAL HABIT TO COUNT DOWN '1000 FT; 500 FT; AND 100 FT TO GO;' WHICH I CLRLY WAS COMPLACENT IN DOING IN THIS SIT. I ALSO PLAN TO MAKE IT MY NEW PRACTICE TO NOTE THAT THE TARGET ALT IS 'ARMED' AND 'CAPTURING;' WITH VERBAL CALLOUTS. I CONSIDER MYSELF TO BE A SAFE; PROCEDURAL PLT AND HAVE NO KNOWN VIOLATIONS TO DATE. I HAVE TAKEN THIS EYE-OPENING EXPERIENCE INTO DEEP CONSIDERATION AND WILL NOT ALLOW THIS INACTION TO OCCUR AGAIN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS VERY KNOWLEDGEABLE ABOUT THE AUTOPLT SYS AND SAYS THAT WHILE THE ACFT IS NEW; THE AUTOPLT TYPE IS NOT A RECENT DESIGN; BUT HAS BEEN THROUGH SEVERAL SOFTWARE UPDATES. THIS SPECIFIC SYS IS UPDATED TO THE LATEST AVAILABLE VERSION.