ACR CREW OVERSHOOTS ALT.

Narrative

I WAS THE FO AND THE PF. THERE WERE SIGNIFICANT TSTMS TO THE N OF THE TAMPA AREA ALONG OUR FILED RTE. DEP CTL CLRED US TO CLB AND MAINTAIN 12000 FT. OUR NORMAL PROC IS FOR THE FO TO RECORD THE PUSHBACK AND TKOF TIMES AND FOR THE PNF TO CALL COMPANY WITH THOSE TIMES ON THE CLBOUT WHEN CLRING 10000 FT. AT 10000 FT; THE CAPT ASKED ME FOR THE TIMES. I LOOKED AT MY PAD AND REALIZED THAT I HAD NOT RECORDED THE TKOF TIME. I LOOKED AT THE CLOCK AND TRIED TO BACK-OUT A REASONABLE TIME. DURING THIS TIME WE WERE GIVEN A FREQ CHANGE TO ZJX. I LOOKED AT THE ALTIMETER TO SEE US PASSING 12000 FT AND RATHER THAN DO A HARD PUSHOVER; ELECTED TO SMOOTHLY BUT POSITIVELY ARREST THE CLB AND DSND TO THE ASSIGNED ALT IN THE INTEREST OF SAFETY AND COMFORT OF THE FLT ATTENDANTS AND PAX. WE PEAKED AT 12600 FT AND DSNDING THROUGH 12500 FT THE CTLR CONFIRMED OUR ASSIGNED 12000 FT ALT SAYING THAT HE SHOWED OUR MODE C RETURN AT 12600 FT. I BELIEVE THAT AT NO TIME WAS THERE ANY TFC CONFLICT; NONE WAS RPTED BY THE CTLR AND AT NO TIME WERE THERE ANY TCASII RETURNS. LATER DISCUSSION WITH THE CAPT CONFIRMED THAT HE THOUGHT THE AUTOPLT WAS ENGAGED AND WAS AWARE OF OUR APCHING 12000 FT BUT ASSUMED THE AUTOPLT WOULD AUTOMATICALLY LEVEL OFF. I ALLOWED MYSELF TO BECOME DISTR BY THE LESS IMPORTANT TASK OF FIGURING OUT TIMES FOR COMPANY RATHER THAN ENSURE THAT OUR COMPLIANCE WITH THE CLRNC. SUPPLEMENTAL INFO FROM ACN 473423: I WAS THINKING THAT THE FO HAD THE AUTOPLT ENGAGED AND THAT HE WAS FLING UTILIZING CTL WHEEL STEERING.