Narrative:

At 10000 ft assigned 6000 ft during descent experienced minor mechanical problem. Dealt with problem and had first officer run checklist. Heard just 1 altitude alert chime then began to level off at 5000 ft. Then noticed 6000 ft in alert window. No known conflict. TCASII gave no alerts, but we possibly went below TCA B floor. First officer was fairly new. I was distracted, and not very concerned with flight path due to high altitude, good visibility, airport in sight, very little traffic. Controller did not seem concerned. Supplemental information from acn 313157: the captain believed he was cleared for the visual approach. I was distracted inside the cockpit and missed the deviation until we were asked by the controller what our altitude was and he cleared us for the visual approach at that time. I'll be more diligent ensuring that PF levels at the correct altitude, especially during visual approachs when everyone is looking outside.

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Original NASA ASRS Text

Title: A B737 FLT DSNDED BELOW CLRNC ALT. CTLR INTERVENED AND ISSUED VISUAL APCH CLRNC.

Narrative: AT 10000 FT ASSIGNED 6000 FT DURING DSCNT EXPERIENCED MINOR MECHANICAL PROB. DEALT WITH PROB AND HAD FO RUN CHKLIST. HEARD JUST 1 ALT ALERT CHIME THEN BEGAN TO LEVEL OFF AT 5000 FT. THEN NOTICED 6000 FT IN ALERT WINDOW. NO KNOWN CONFLICT. TCASII GAVE NO ALERTS, BUT WE POSSIBLY WENT BELOW TCA B FLOOR. FO WAS FAIRLY NEW. I WAS DISTRACTED, AND NOT VERY CONCERNED WITH FLT PATH DUE TO HIGH ALT, GOOD VISIBILITY, ARPT IN SIGHT, VERY LITTLE TFC. CTLR DID NOT SEEM CONCERNED. SUPPLEMENTAL INFO FROM ACN 313157: THE CAPT BELIEVED HE WAS CLRED FOR THE VISUAL APCH. I WAS DISTRACTED INSIDE THE COCKPIT AND MISSED THE DEV UNTIL WE WERE ASKED BY THE CTLR WHAT OUR ALT WAS AND HE CLRED US FOR THE VISUAL APCH AT THAT TIME. I'LL BE MORE DILIGENT ENSURING THAT PF LEVELS AT THE CORRECT ALT, ESPECIALLY DURING VISUAL APCHS WHEN EVERYONE IS LOOKING OUTSIDE.

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.