Narrative:

On the spica arrival into dtw, ZOB cleared us to cross spica at 12000 ft MSL. We had 12000 ft in the FMS as a crossing restr we expected. As we approached spica in the descent, I thought the aircraft operating in the managed descent mode may not make the restr, so I switched to the vertical speed mode and increased the rate of descent to assure the restr was complied with. As the aircraft leveled at 11000 ft, I looked at the FMS altitude of 12000 ft at spica and at the altitude selected on the autoplt (11000 ft) and realized there was a problem. What altitude were we cleared to? I asked the captain (PNF) who had been busy on the radios and accomplishing checklists. He had doubts and asked the controller if we were cleared to 11000 ft. The controller replied '11000 ft is fine.' as we thought about it, neither of us heard a clearance to 11000 ft and we realized we had 'busted' the 12000 ft clearance issued earlier in descent. I try to be diligent in verifying the selected altitudes on the fmp (autoplt) as per SOP. I either slipped mentally and selected 11000 ft or selected 12000 ft and then bumped it 1 click to 11000 ft as I pulled my fingers off the knob. I've done this before and caught it. In either case, I failed to verify the altitude properly with the PNF as per S0P nor he did catch my mistake. For me personally, the highly automated A320/319 has become a battle against complacency, one to fight every day.

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Original NASA ASRS Text

Title: ALTDEV DURING DSCNT TO DTW, MI.

Narrative: ON THE SPICA ARR INTO DTW, ZOB CLRED US TO CROSS SPICA AT 12000 FT MSL. WE HAD 12000 FT IN THE FMS AS A XING RESTR WE EXPECTED. AS WE APCHED SPICA IN THE DSCNT, I THOUGHT THE ACFT OPERATING IN THE MANAGED DSCNT MODE MAY NOT MAKE THE RESTR, SO I SWITCHED TO THE VERT SPD MODE AND INCREASED THE RATE OF DSCNT TO ASSURE THE RESTR WAS COMPLIED WITH. AS THE ACFT LEVELED AT 11000 FT, I LOOKED AT THE FMS ALT OF 12000 FT AT SPICA AND AT THE ALT SELECTED ON THE AUTOPLT (11000 FT) AND REALIZED THERE WAS A PROB. WHAT ALT WERE WE CLRED TO? I ASKED THE CAPT (PNF) WHO HAD BEEN BUSY ON THE RADIOS AND ACCOMPLISHING CHKLISTS. HE HAD DOUBTS AND ASKED THE CTLR IF WE WERE CLRED TO 11000 FT. THE CTLR REPLIED '11000 FT IS FINE.' AS WE THOUGHT ABOUT IT, NEITHER OF US HEARD A CLRNC TO 11000 FT AND WE REALIZED WE HAD 'BUSTED' THE 12000 FT CLRNC ISSUED EARLIER IN DSCNT. I TRY TO BE DILIGENT IN VERIFYING THE SELECTED ALTS ON THE FMP (AUTOPLT) AS PER SOP. I EITHER SLIPPED MENTALLY AND SELECTED 11000 FT OR SELECTED 12000 FT AND THEN BUMPED IT 1 CLICK TO 11000 FT AS I PULLED MY FINGERS OFF THE KNOB. I'VE DONE THIS BEFORE AND CAUGHT IT. IN EITHER CASE, I FAILED TO VERIFY THE ALT PROPERLY WITH THE PNF AS PER S0P NOR HE DID CATCH MY MISTAKE. FOR ME PERSONALLY, THE HIGHLY AUTOMATED A320/319 HAS BECOME A BATTLE AGAINST COMPLACENCY, ONE TO FIGHT EVERY DAY.

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.