Narrative:

We were cleared down to 11000 ft initially. While the first officer was flying and I was talking to the back to ensure they were prepared for landing; ATC said; 'level off at 12000 ft air carrier X.' when the first officer reselected the altitude to 12000 ft; the autoplt must not have armed the capture mode. I looked up and saw 250 ft below altitude and heard 'altitude.' we clicked off the autoplt and climbed back to the assigned altitude. The MD88/90 is infamous for not capturing the altitude; and the first officer is just off of furlough. I should have been monitoring his leveloff as I spoke to the crew on the interphone. ATC did not notice or at least did not call us to tell us. It must have happened in between ATC radar sweeps.

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Original NASA ASRS Text

Title: FLT CREW OF MD90 EXPERIENCE ALTDEV WHEN AUTOPLT ALT CAPTURE FAILS TO ARREST DSCNT AT CLRED ALT.

Narrative: WE WERE CLRED DOWN TO 11000 FT INITIALLY. WHILE THE FO WAS FLYING AND I WAS TALKING TO THE BACK TO ENSURE THEY WERE PREPARED FOR LNDG; ATC SAID; 'LEVEL OFF AT 12000 FT ACR X.' WHEN THE FO RESELECTED THE ALT TO 12000 FT; THE AUTOPLT MUST NOT HAVE ARMED THE CAPTURE MODE. I LOOKED UP AND SAW 250 FT BELOW ALT AND HEARD 'ALT.' WE CLICKED OFF THE AUTOPLT AND CLBED BACK TO THE ASSIGNED ALT. THE MD88/90 IS INFAMOUS FOR NOT CAPTURING THE ALT; AND THE FO IS JUST OFF OF FURLOUGH. I SHOULD HAVE BEEN MONITORING HIS LEVELOFF AS I SPOKE TO THE CREW ON THE INTERPHONE. ATC DID NOT NOTICE OR AT LEAST DID NOT CALL US TO TELL US. IT MUST HAVE HAPPENED IN BTWN ATC RADAR SWEEPS.

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.