Narrative:

We were cleared to cross clipr intersection at 12000 ft. Autoplt was engaged and a managed descent was programmed into the FMGC so as to cross clipr at 12000 ft. I was monitoring the descent from FL200 and approaching clipr. It looked like the autoplt/FMGC were just barely going to make the 12000 ft restr. When I could tell we were going to be close, I tried to expedite the descent by selecting 'open descent' mode. Since the autoplt/FMGC were still carrying power about idle, I selected open descent to bring the thrust to idle and thereby increase the rate of descent. As soon as I selected open descent, the thrust went to idle as required. However, the aircraft immediately began slowing to a slower airspeed (economy descent airspeed). While slowing to economy descent airspeed, my descent rate decreased dramatically. Passing over clipr, 'altitude capture' mode engaged, but we were at 12600 ft. In hindsight, if I had just left the managed descent continue, the aircraft would have hit clipr at 12000 ft or slightly higher (ie, 100 ft). My attempt to correct for this minor deviation resulted in a much higher deviation. In the future, I am confident I can identify if the aircraft/autoplt are deviating from expectations and if necessary I can intervene earlier to ensure restrs are met.

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Original NASA ASRS Text

Title: A320 AIRBUS FO FAILED TO MAKE XING ALT DUE TO RETARDING THE DSCNT RATE BY THE AUTOFLT FMS.

Narrative: WE WERE CLRED TO CROSS CLIPR INTXN AT 12000 FT. AUTOPLT WAS ENGAGED AND A MANAGED DSCNT WAS PROGRAMMED INTO THE FMGC SO AS TO CROSS CLIPR AT 12000 FT. I WAS MONITORING THE DSCNT FROM FL200 AND APCHING CLIPR. IT LOOKED LIKE THE AUTOPLT/FMGC WERE JUST BARELY GOING TO MAKE THE 12000 FT RESTR. WHEN I COULD TELL WE WERE GOING TO BE CLOSE, I TRIED TO EXPEDITE THE DSCNT BY SELECTING 'OPEN DSCNT' MODE. SINCE THE AUTOPLT/FMGC WERE STILL CARRYING PWR ABOUT IDLE, I SELECTED OPEN DSCNT TO BRING THE THRUST TO IDLE AND THEREBY INCREASE THE RATE OF DSCNT. AS SOON AS I SELECTED OPEN DSCNT, THE THRUST WENT TO IDLE AS REQUIRED. HOWEVER, THE ACFT IMMEDIATELY BEGAN SLOWING TO A SLOWER AIRSPD (ECONOMY DSCNT AIRSPD). WHILE SLOWING TO ECONOMY DSCNT AIRSPD, MY DSCNT RATE DECREASED DRAMATICALLY. PASSING OVER CLIPR, 'ALT CAPTURE' MODE ENGAGED, BUT WE WERE AT 12600 FT. IN HINDSIGHT, IF I HAD JUST LEFT THE MANAGED DSCNT CONTINUE, THE ACFT WOULD HAVE HIT CLIPR AT 12000 FT OR SLIGHTLY HIGHER (IE, 100 FT). MY ATTEMPT TO CORRECT FOR THIS MINOR DEV RESULTED IN A MUCH HIGHER DEV. IN THE FUTURE, I AM CONFIDENT I CAN IDENT IF THE ACFT/AUTOPLT ARE DEVIATING FROM EXPECTATIONS AND IF NECESSARY I CAN INTERVENE EARLIER TO ENSURE RESTRS ARE MET.

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.