Narrative:

While climbing to an assigned altitude of FL240 in ZTL's airspace; we passed through FL240 and climbed to FL246 before corrective action was taken to descend back to FL240. The autoplt was engaged and the flight director was in the 'climb' mode passing FL230; both pilots called out 'FL230 climbing to FL240; altitude armed' per our standard operating procedures. At approximately FL232; the PF looked down in the cockpit and picked up some paperwork. While reading the paperwork and somewhere between FL230 and FL240; the altitude capture function on the autoplt/flight director disengaged. As a result; the aircraft did not level at FL240; but continued a climb through the assigned altitude; unnoticed by both flight crew members; to approximately FL246. At this time; the PF noticed the deviation and started to recover the aircraft back to FL240. At the same time of the recovery; ZTL queried the crew of their altitude. Additionally; a TA alerted the crew of a nearby aircraft followed by an RA. The PF was already establishing a descent and the RA event ceased. Once the aircraft was returned to FL240; the remainder of the flight was uneventful. I believe the reason for this deviation was loss of situational awareness due to both crew members being distraction with non pertinent cockpit duties during a critical phase of flight. Additionally; 'trusting' the autoplt to level off at the proper altitude without pilot monitoring. Ways to help prevent this from occurring in the future is to ensure all flight crew perform only the duties required for the particular phase of flight the aircraft is in. Also; to confirm that one pilot is always in control of the aircraft at all times. Ensure positive xfer of controls between the flight crew if a situation requires the attention of the other crew member. Finally; never trust an aircraft system to work 100% of the time. The autoplt; like any other system on board an aircraft; including the flight crew; is very reliable but not perfect. To achieve the highest probability for a safe flight each and every time; the flight crew must monitor all system on board the aircraft; including each other to provide the level of redundancy required to operate safely and efficiently in today's airspace system.

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Original NASA ASRS Text

Title: B350 CLBS THROUGH ASSIGNED ALT WHEN ALT CAPTURE MODE FAILS. FLT CREW DISTR BY NON ESSENTIAL COCKPIT ACTIVITIES.

Narrative: WHILE CLBING TO AN ASSIGNED ALT OF FL240 IN ZTL'S AIRSPACE; WE PASSED THROUGH FL240 AND CLBED TO FL246 BEFORE CORRECTIVE ACTION WAS TAKEN TO DSND BACK TO FL240. THE AUTOPLT WAS ENGAGED AND THE FLT DIRECTOR WAS IN THE 'CLB' MODE PASSING FL230; BOTH PLTS CALLED OUT 'FL230 CLBING TO FL240; ALT ARMED' PER OUR STANDARD OPERATING PROCS. AT APPROX FL232; THE PF LOOKED DOWN IN THE COCKPIT AND PICKED UP SOME PAPERWORK. WHILE READING THE PAPERWORK AND SOMEWHERE BTWN FL230 AND FL240; THE ALT CAPTURE FUNCTION ON THE AUTOPLT/FLT DIRECTOR DISENGAGED. AS A RESULT; THE ACFT DID NOT LEVEL AT FL240; BUT CONTINUED A CLB THROUGH THE ASSIGNED ALT; UNNOTICED BY BOTH FLT CREW MEMBERS; TO APPROX FL246. AT THIS TIME; THE PF NOTICED THE DEV AND STARTED TO RECOVER THE ACFT BACK TO FL240. AT THE SAME TIME OF THE RECOVERY; ZTL QUERIED THE CREW OF THEIR ALT. ADDITIONALLY; A TA ALERTED THE CREW OF A NEARBY ACFT FOLLOWED BY AN RA. THE PF WAS ALREADY ESTABLISHING A DSCNT AND THE RA EVENT CEASED. ONCE THE ACFT WAS RETURNED TO FL240; THE REMAINDER OF THE FLT WAS UNEVENTFUL. I BELIEVE THE REASON FOR THIS DEV WAS LOSS OF SITUATIONAL AWARENESS DUE TO BOTH CREW MEMBERS BEING DISTR WITH NON PERTINENT COCKPIT DUTIES DURING A CRITICAL PHASE OF FLT. ADDITIONALLY; 'TRUSTING' THE AUTOPLT TO LEVEL OFF AT THE PROPER ALT WITHOUT PLT MONITORING. WAYS TO HELP PREVENT THIS FROM OCCURRING IN THE FUTURE IS TO ENSURE ALL FLT CREW PERFORM ONLY THE DUTIES REQUIRED FOR THE PARTICULAR PHASE OF FLT THE ACFT IS IN. ALSO; TO CONFIRM THAT ONE PLT IS ALWAYS IN CTL OF THE ACFT AT ALL TIMES. ENSURE POSITIVE XFER OF CTLS BTWN THE FLT CREW IF A SITUATION REQUIRES THE ATTN OF THE OTHER CREW MEMBER. FINALLY; NEVER TRUST AN ACFT SYS TO WORK 100% OF THE TIME. THE AUTOPLT; LIKE ANY OTHER SYS ON BOARD AN ACFT; INCLUDING THE FLT CREW; IS VERY RELIABLE BUT NOT PERFECT. TO ACHIEVE THE HIGHEST PROBABILITY FOR A SAFE FLT EACH AND EVERY TIME; THE FLT CREW MUST MONITOR ALL SYS ON BOARD THE ACFT; INCLUDING EACH OTHER TO PROVIDE THE LEVEL OF REDUNDANCY REQUIRED TO OPERATE SAFELY AND EFFICIENTLY IN TODAY'S AIRSPACE SYS.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.