Narrative:

After takeoff from runway 36L departure assigned us a heading of 270 degrees and cleared us to 12000'. We set 12000' in the altitude selector and initiated our turn. At some point thereafter, the altitude selector was inadvertently bumped to 13000' or the initial setting to 12000' was in error and I missed the error). We climbed through 12000'. At 12500' I questioned myself about the assigned altitude. At about the time control departure asked if we were leveling at 12000' or going to 13000'. We questioned clt as to the correct assigned altitude at which point clt handed us off to ZTL. Contributing factors: WX--trw's 5 mi south of airport, moderate rw's 3-5 mi north of runway 36L, turbulence reported in airport area. Communications: 1) F/a's had mentioned they wished to provide meal service from clt to chs. I told them to remain seated until we could assess the WX once airborne. 20 handoff from tower to departure and subsequent clearance to 12000' occurred while negotiating WX off end of runway 36L. Upon reaching 10000' I left the frequency to call back to the F/a's on the interphone, to inform them of flight conditions. Switched radio selector panel back to #1 radio as the thousand ft to go audible sounded. I noted our altitude as we were through 21500'. At that time clt questioned us and handed us off to ZTL. Equipment: altitude selector lacks visibility prominence and is easily bumped to an incorrect setting. The possibility of an uncommanded MCP altitude display change does exist.

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Original NASA ASRS Text

Title: DEVIATION FROM ASSIGNED ALT.

Narrative: AFTER TKOF FROM RWY 36L DEP ASSIGNED US A HDG OF 270 DEGS AND CLRED US TO 12000'. WE SET 12000' IN THE ALT SELECTOR AND INITIATED OUR TURN. AT SOME POINT THEREAFTER, THE ALT SELECTOR WAS INADVERTENTLY BUMPED TO 13000' OR THE INITIAL SETTING TO 12000' WAS IN ERROR AND I MISSED THE ERROR). WE CLBED THROUGH 12000'. AT 12500' I QUESTIONED MYSELF ABOUT THE ASSIGNED ALT. AT ABOUT THE TIME CTL DEP ASKED IF WE WERE LEVELING AT 12000' OR GOING TO 13000'. WE QUESTIONED CLT AS TO THE CORRECT ASSIGNED ALT AT WHICH POINT CLT HANDED US OFF TO ZTL. CONTRIBUTING FACTORS: WX--TRW'S 5 MI S OF ARPT, MODERATE RW'S 3-5 MI N OF RWY 36L, TURB RPTED IN ARPT AREA. COMS: 1) F/A'S HAD MENTIONED THEY WISHED TO PROVIDE MEAL SVC FROM CLT TO CHS. I TOLD THEM TO REMAIN SEATED UNTIL WE COULD ASSESS THE WX ONCE AIRBORNE. 20 HDOF FROM TWR TO DEP AND SUBSEQUENT CLRNC TO 12000' OCCURRED WHILE NEGOTIATING WX OFF END OF RWY 36L. UPON REACHING 10000' I LEFT THE FREQ TO CALL BACK TO THE F/A'S ON THE INTERPHONE, TO INFORM THEM OF FLT CONDITIONS. SWITCHED RADIO SELECTOR PANEL BACK TO #1 RADIO AS THE THOUSAND FT TO GO AUDIBLE SOUNDED. I NOTED OUR ALT AS WE WERE THROUGH 21500'. AT THAT TIME CLT QUESTIONED US AND HANDED US OFF TO ZTL. EQUIP: ALT SELECTOR LACKS VIS PROMINENCE AND IS EASILY BUMPED TO AN INCORRECT SETTING. THE POSSIBILITY OF AN UNCOMMANDED MCP ALT DISPLAY CHANGE DOES EXIST.

Data retrieved from NASA's ASRS site as of July 2007 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.