ACR MLG ALT DEVIATION OVERSHOT CRUISE ALT.

Narrative

TKOF AND DEP WERE NORMAL. THE WX WAS GOOD; HOWEVER; THERE WERE BUILDUPS IN THE AREA. AT THE TIME OF THE INCIDENT WE WERE TRYING TO NAV AROUND A BUILDUP USING RADAR. JUST PRIOR TO LEVEL OFF AT 13000' THE ACFT ENTERED THE TOP OF A BUILDUP EXPERIENCING MODERATE TURB; HVY RAIN AND ST ELMO'S FIRE. THE CAPT; WHO WAS FLYING AT THE TIME; WAS ADJUSTING THE RATE OF CLB FOR AN AUTOCAPTURE WHEN THE BUILD UP WAS ENTERED. HIS ATTN WAS DIVERTED TO THE AUTO THROTTLES AND TRYING TO SLOW TO TURB PENETRATION SPD. SINCE THERE WAS HVY RAIN; IGNITION WAS CALLED FOR. SUDDENLY THE ALT ALERTER CALLED OUT 'ALT.' WE WERE STILL CLBING THROUGH 13000' AND PASSING 13300'. ACTION WAS TAKEN TO REVERSE THE CLB; BUT THE ACFT REACHED 13500' BEFORE A REVERSAL WAS ACHIEVED. CENTER ADVISED THAT MODE C READOUT SHOWED 13400'; HOWEVER BY THAT TIME WE'D REACHED OUR ORIGINAL LEVEL OFF ALT OF 13000'. WE RPTED LEVEL AT 13000'. THE CAUSE OF THE INCIDENT WAS THE SELECTION OF VERT SPD DURING AUTOCAPTURE; THUS CANCELLING THE AUTOCAPTURE. ALSO THE DIVERSION OF THE CAPT'S ATTN TO SPD REDUCTION AND THE HDOF FROM DEP TO CENTER DURING LEVEL OFF CAUSED THE CREW TO NOT XCHK THE FLT MODE ANNUNCIATOR AND MONITOR THE LEVEL OFF. CONTRIBUTING TO THE INCIDENT WERE THE F/O'S RELATIVE INEXPERIENCE BOTH IN TOTAL TIME AND IN TYPE OF EQUIP. WE WERE BOTH TAKEN BY SURPRISE WHEN WE ENTERED THE BUILDUP; HOWEVER HE SEEMED FROZEN AND MESMERIZED BY WHAT WAS HAPPENING OUTSIDE. I DON'T THINK HE'D EVER SEEN ST ELMO'S FIRE BEFORE. AS I'D FIND OUT LATER; HE DIDN'T HAVE MUCH EXPERIENCE WITH THE PARTICULAR MODEL WE WERE OPERATING. WITH THE RELATIVELY COMPLEX INSTRUMENTATION AND AUTOTHROTTLES; IT TAKES A GOOD OPERATIONAL KNOWLEDGE OF HOW THE EQUIP WORKS. THIS MODEL CONSTITUTES LESS THAN 20% OF OUR FLEET AND IT'S NOT UNCOMMON TO NOT FLY THIS PARTICULAR MODEL FOR 2 WKS OR TO FLY 3 DIFFERENT MODELS IN 1 DAY. FINALLY; THE PERFECT TIMING OF ALL THE EVENTS OCCURRING AT ONCE MULTIPLIED ALL THE FACTORS LEADING UP TO THE EVENT. BETTER CREW COORD AND EXPERIENCE IN THE ACFT COULD HAVE POSSIBLY PREVENTED THE INCIDENT. ALSO THE NEED FOR THE PF TO DO JUST THAT; IE; TRY NOT TO DO TOO MUCH AT ONCE. THE SPD REDUCTION COULD HAVE WAITED UNTIL THE LEVEL OFF WAS ACHIEVED AND THE RADIO CALL COULD HAVE BEEN POSTPONED UNTIL THE SITUATION WAS UNDER CTL.