Narrative:

In process of diverting to alternate after exiting holding. Autoplt engaged in descent to capture FL240. I was in process of getting WX, checking NOTAMS when I heard first officer say something about below altitude. When I looked forward we were about 250 ft low, and the captain was hand flying aircraft back to correct altitude. We were questioned for altitude confirmation by ATC, by then we were level. I believe autoplt, for some reason overshot altitude without warning while in normal descent rate and normal flight mode annunciators. It was a very busy phase of flight with the holding, alternate change, talking to company, figuring fuel required, briefing arrs, approachs, one 5 second miss of altitude scan caused this deviation.

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Original NASA ASRS Text

Title: CAPT OF A WDB CARGO ACR OVERSHOT DSCNT ALT WHEN THE AUTOPLT FAILED TO CAPTURE THE ASSIGNED PROGRAMMED ALT. THE FO FIRST NOTED THE OVERSIGHT AND THE CAPT CORRECTED AT ONCE LOSING 250 FT BEFORE RETURNING TO ASSIGNED.

Narrative: IN PROCESS OF DIVERTING TO ALTERNATE AFTER EXITING HOLDING. AUTOPLT ENGAGED IN DSCNT TO CAPTURE FL240. I WAS IN PROCESS OF GETTING WX, CHKING NOTAMS WHEN I HEARD FO SAY SOMETHING ABOUT BELOW ALT. WHEN I LOOKED FORWARD WE WERE ABOUT 250 FT LOW, AND THE CAPT WAS HAND FLYING ACFT BACK TO CORRECT ALT. WE WERE QUESTIONED FOR ALT CONFIRMATION BY ATC, BY THEN WE WERE LEVEL. I BELIEVE AUTOPLT, FOR SOME REASON OVERSHOT ALT WITHOUT WARNING WHILE IN NORMAL DSCNT RATE AND NORMAL FLT MODE ANNUNCIATORS. IT WAS A VERY BUSY PHASE OF FLT WITH THE HOLDING, ALTERNATE CHANGE, TALKING TO COMPANY, FIGURING FUEL REQUIRED, BRIEFING ARRS, APCHS, ONE 5 SECOND MISS OF ALT SCAN CAUSED THIS DEV.

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.