Narrative:

I was PNF from bwi to mdw. We were cleared down to flight FL250 and made the appropriate call outs while passing fl 260. I do not recall exactly what I was doing at the moment of the deviation, but became aware that we passed fl 250 when the altitude alert went off. At the time the fp stopped the descent and climbed back to FL250. We received traffic alerts slow as FL244 with no breach of separation from any other aircraft. The flight continued to mdw without incident. As a preventive measure, I feel that while performing PNF duties, I should always keep a watchful eye on all level offs. If need be, stop anything that you are doing during the last 1000 ft until a successful level off has been completed. Since this aircraft was a B737-200, this vigilance can not be stressed enough.

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Original NASA ASRS Text

Title: B737 FLC ENRTE TO MDW, OVERSHOT ASSIGNED ALT WHILE DESCENDING.

Narrative: I WAS PNF FROM BWI TO MDW. WE WERE CLRED DOWN TO FLT FL250 AND MADE THE APPROPRIATE CALL OUTS WHILE PASSING FL 260. I DO NOT RECALL EXACTLY WHAT I WAS DOING AT THE MOMENT OF THE DEVIATION, BUT BECAME AWARE THAT WE PASSED FL 250 WHEN THE ALTITUDE ALERT WENT OFF. AT THE TIME THE FP STOPPED THE DESCENT AND CLIMBED BACK TO FL250. WE RECEIVED TFC ALERTS SLOW AS FL244 WITH NO BREACH OF SEPARATION FROM ANY OTHER ACFT. THE FLT CONTINUED TO MDW WITHOUT INCIDENT. AS A PREVENTIVE MEASURE, I FEEL THAT WHILE PERFORMING PNF DUTIES, I SHOULD ALWAYS KEEP A WATCHFUL EYE ON ALL LEVEL OFFS. IF NEED BE, STOP ANYTHING THAT YOU ARE DOING DURING THE LAST 1000 FT UNTIL A SUCCESSFUL LEVEL OFF HAS BEEN COMPLETED. SINCE THIS ACFT WAS A B737-200, THIS VIGILANCE CAN NOT BE STRESSED ENOUGH.

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.