Narrative:

On approach to buffalo, ny we were given a descent to 11000 ft. I was flying. At our usual descent rate of 3 mi per 1000 ft, the descent clearance was given about 5 mi late. To increase our descent rate, I increased our speed with the autoplt controls. The autoplt dove for the airspeed too aggressively, and I restrained the control column. This action must have disconnected the performance management part of the autoplt but left the basic functions still engaged. As stated, we were cleared to 11000 ft. At 10800 ft both pilots noticed the autoplt not leveling off, I disengaged the autoplt and at 10600, recovered, and climbed back up to 11000 ft. Contributing factors were late descent clearance and high descent rate. We were alerted by the aural warning. Corrective action would be to monitor the altitude more closely and when using this particular autoplt to make more frequent checks to make sure the autoplt has not inadvertently partially disengaged. Supplemental information from acn 301920: I was off getting the ATIS. We had both agreed on the descent to 11000 ft in the altitude select window. We were descending at 6000 FPM. I can't remember if we did but I'm fairly sure we both called '12 for 11.' as the aircraft passed through 11000 ft I called out to pull up to 11000 ft, since the altitude select was knocked off.

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Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT IN DSCNT PROC.

Narrative: ON APCH TO BUFFALO, NY WE WERE GIVEN A DSCNT TO 11000 FT. I WAS FLYING. AT OUR USUAL DSCNT RATE OF 3 MI PER 1000 FT, THE DSCNT CLRNC WAS GIVEN ABOUT 5 MI LATE. TO INCREASE OUR DSCNT RATE, I INCREASED OUR SPD WITH THE AUTOPLT CTLS. THE AUTOPLT DOVE FOR THE AIRSPD TOO AGGRESSIVELY, AND I RESTRAINED THE CTL COLUMN. THIS ACTION MUST HAVE DISCONNECTED THE PERFORMANCE MGMNT PART OF THE AUTOPLT BUT LEFT THE BASIC FUNCTIONS STILL ENGAGED. AS STATED, WE WERE CLRED TO 11000 FT. AT 10800 FT BOTH PLTS NOTICED THE AUTOPLT NOT LEVELING OFF, I DISENGAGED THE AUTOPLT AND AT 10600, RECOVERED, AND CLBED BACK UP TO 11000 FT. CONTRIBUTING FACTORS WERE LATE DSCNT CLRNC AND HIGH DSCNT RATE. WE WERE ALERTED BY THE AURAL WARNING. CORRECTIVE ACTION WOULD BE TO MONITOR THE ALT MORE CLOSELY AND WHEN USING THIS PARTICULAR AUTOPLT TO MAKE MORE FREQUENT CHKS TO MAKE SURE THE AUTOPLT HAS NOT INADVERTENTLY PARTIALLY DISENGAGED. SUPPLEMENTAL INFO FROM ACN 301920: I WAS OFF GETTING THE ATIS. WE HAD BOTH AGREED ON THE DSCNT TO 11000 FT IN THE ALT SELECT WINDOW. WE WERE DSNDING AT 6000 FPM. I CAN'T REMEMBER IF WE DID BUT I'M FAIRLY SURE WE BOTH CALLED '12 FOR 11.' AS THE ACFT PASSED THROUGH 11000 FT I CALLED OUT TO PULL UP TO 11000 FT, SINCE THE ALT SELECT WAS KNOCKED OFF.

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.