Narrative:

The flight we were working was en route to ewr. The first officer was the PF. During the williamsport 1 arrival, while descending to cross sweet intersection at 7000 ft, the first officer had the autoplt engaged. Descending through 9000 ft (approximately), ATC asked us to reduce speed from 250 KTS to 210 KTS while descending. The first officer decided to use the speed brakes, with the autoplt still on. He then decided to temporarily disengage the autoplt to smooth the descent. I (the captain, PNF) was monitoring the descent progress while calling operations. 7000 ft was set in the altitude select. Approaching 7000 ft, with a descent rate of approximately 2500 FPM, the first officer released the button and the autoplt passed through 7000 ft. He (the first officer) retracted the speed brakes, and when I finally looked up a few seconds later, I observed 6400 ft on the altimeter. I immediately challenged him and simultaneously pulled back to initiate a climb. The autoplt was then disengaged completely and aircraft was hand flown to altitude.

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Original NASA ASRS Text

Title: DSNDING WITH AUTOPLT TEMPORARILY DEACTIVATED AND SPD BRAKES EXTENDED TO FACILITATE A SPD REDUCTION DURING DSCNT, THE PLT ELECTS TO RE-ESTABLISH THE AUTOPLT, BUT FINDS THE ENSUING LEVELOFF AT THE ASSIGNED ALT IS BEYOND ITS CAPABILITY. THE RESULT IS AN ALT OVERSHOOT.

Narrative: THE FLT WE WERE WORKING WAS ENRTE TO EWR. THE FO WAS THE PF. DURING THE WILLIAMSPORT 1 ARR, WHILE DSNDING TO CROSS SWEET INTXN AT 7000 FT, THE FO HAD THE AUTOPLT ENGAGED. DSNDING THROUGH 9000 FT (APPROX), ATC ASKED US TO REDUCE SPD FROM 250 KTS TO 210 KTS WHILE DSNDING. THE FO DECIDED TO USE THE SPD BRAKES, WITH THE AUTOPLT STILL ON. HE THEN DECIDED TO TEMPORARILY DISENGAGE THE AUTOPLT TO SMOOTH THE DSCNT. I (THE CAPT, PNF) WAS MONITORING THE DSCNT PROGRESS WHILE CALLING OPS. 7000 FT WAS SET IN THE ALT SELECT. APCHING 7000 FT, WITH A DSCNT RATE OF APPROX 2500 FPM, THE FO RELEASED THE BUTTON AND THE AUTOPLT PASSED THROUGH 7000 FT. HE (THE FO) RETRACTED THE SPD BRAKES, AND WHEN I FINALLY LOOKED UP A FEW SECONDS LATER, I OBSERVED 6400 FT ON THE ALTIMETER. I IMMEDIATELY CHALLENGED HIM AND SIMULTANEOUSLY PULLED BACK TO INITIATE A CLB. THE AUTOPLT WAS THEN DISENGAGED COMPLETELY AND ACFT WAS HAND FLOWN TO ALT.

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.