Narrative:

We were at FL370 cleared to FL240. I was PNF and set FL240 in FCU and both PF and I agreed. PF thought it was our discretion and I said it was not. He then said he'd use V/south at 1000/min as we were not at optimal descent point. I was looking at boids arrival page when PF said something. I looked up and saw we were at FL380. Copilot went to open descent. At FL382 ATC asked our altitude. He thought his encoder was wrong. We said what happened, and he said to expedite through FL310 our discretion after. We do not know if we conflicted with anyone else. This incident re-emphasizes the extra care with an automatic airplane one must exercise to make sure it does what you want. Interestingly, no altitude alert was sounded and I don't recall if the altitude window was flashing. Callback conversation with reporter revealed the following information: because the captain's report didn't specify why the aircraft climbed when the flight crew had been cleared to descend, the reporter was contacted. He said that, though he wasn't sure why it occurred, he assumed that the first officer had set a vertical climb of 1000 FPM instead of the descent. Since that action would generally be considered something an inexperienced pilot on the aircraft might do, the captain was asked about the first officer experience level. He had his records of flts available so clarified that the first officer was very experienced on the aircraft, and must have been distracted by some other task when he initiated what he thought was a descent. Reporter said that his company has included in the annual proficiency check more advanced training on the A320 computer system, which he believes is very positive and necessary.

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Original NASA ASRS Text

Title: AFTER BEING CLRED TO LOWER ALT, PF INTENDED TO SET A DSCNT OF 1000 FPM IN THE MCU (MODE CTRL PANEL), BUT APPARENTLY, INSTEAD OF SETTING IN A DSCNT, SET IN A CLB. NEITHER OF THE FLC NOTICED UNTIL ATC INTERVENED WHEN THEIR ALT WAS 1200 FT ABOVE THE ORIGINAL ALT.

Narrative: WE WERE AT FL370 CLRED TO FL240. I WAS PNF AND SET FL240 IN FCU AND BOTH PF AND I AGREED. PF THOUGHT IT WAS OUR DISCRETION AND I SAID IT WAS NOT. HE THEN SAID HE'D USE V/S AT 1000/MIN AS WE WERE NOT AT OPTIMAL DSCNT POINT. I WAS LOOKING AT BOIDS ARRIVAL PAGE WHEN PF SAID SOMETHING. I LOOKED UP AND SAW WE WERE AT FL380. COPLT WENT TO OPEN DSCNT. AT FL382 ATC ASKED OUR ALT. HE THOUGHT HIS ENCODER WAS WRONG. WE SAID WHAT HAPPENED, AND HE SAID TO EXPEDITE THROUGH FL310 OUR DISCRETION AFTER. WE DO NOT KNOW IF WE CONFLICTED WITH ANYONE ELSE. THIS INCIDENT RE-EMPHASIZES THE EXTRA CARE WITH AN AUTOMATIC AIRPLANE ONE MUST EXERCISE TO MAKE SURE IT DOES WHAT YOU WANT. INTERESTINGLY, NO ALT ALERT WAS SOUNDED AND I DON'T RECALL IF THE ALT WINDOW WAS FLASHING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: BECAUSE THE CAPT'S RPT DIDN'T SPECIFY WHY THE ACFT CLBED WHEN THE FLC HAD BEEN CLRED TO DSND, THE RPTR WAS CONTACTED. HE SAID THAT, THOUGH HE WASN'T SURE WHY IT OCCURRED, HE ASSUMED THAT THE FO HAD SET A VERT CLB OF 1000 FPM INSTEAD OF THE DSCNT. SINCE THAT ACTION WOULD GENERALLY BE CONSIDERED SOMETHING AN INEXPERIENCED PLT ON THE ACFT MIGHT DO, THE CAPT WAS ASKED ABOUT THE FO EXPERIENCE LEVEL. HE HAD HIS RECORDS OF FLTS AVAILABLE SO CLARIFIED THAT THE FO WAS VERY EXPERIENCED ON THE ACFT, AND MUST HAVE BEEN DISTRACTED BY SOME OTHER TASK WHEN HE INITIATED WHAT HE THOUGHT WAS A DSCNT. RPTR SAID THAT HIS COMPANY HAS INCLUDED IN THE ANNUAL PROFICIENCY CHK MORE ADVANCED TRAINING ON THE A320 COMPUTER SYS, WHICH HE BELIEVES IS VERY POSITIVE AND NECESSARY.

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.