AN ACR A320 FLC EXCEEDS 250 KIAS BELOW 10000 FT WHEN THE FO; ON HIS IOE; SELECTS 'OPEN DSCNT' MODE ON THE AUTOFLT SYS. THE CAPT NOTES THE HIGH SPD AT 9700 FT AND INSTRUCTS THE FO TO SLOW.

Narrative

WE WERE ON THE PULLMAN FOUR ARR TO ORD BTWN PIVOT AND STOREY; LEVEL AT 12000 FT; 300 KTS (BEST FORWARD SPD). WE WERE SWITCHED TO CHICAGO APCH. APCH CLRED US TO 10000 FT. FO BEGAN DSCNT WITH AUTOPLT ENGAGED. AT APPROX 10500 FT; APCH CTL CLRED US TO 8000 FT; PNF (ME) SET ALT ALERTER TO 8000 FT. FO POINTED TO NEW ALT AND REPEATED '8000' FT. AS ACFT APCHED 10000 FT; FO PUSHED VERT SPD KNOB (PUSH TO LEVEL OFF) ACFT BEGAN TO SLOW; BUT CONTINUED TO DSND BELOW 10000 FT TO APPROX 9700 FT AS SPD SLOWED TO 280- 270-265-260-250 KTS. I DIRECTED FO TO AGGRESSIVELY SLOW AND CLB BACK 10000 FT. HE SLOWED THE ACFT; BUT ONLY GOT BACK UP TO TO 9800 FT BEFORE SPD REACHED 250 KTS. CONTINUED DSCNT FOR ROUTINE APCH AND LNDG. PROB AROSE DUE TO INEXPERIENCED COPLT AND HIS OVER-RELIANCE ON AUTOFLT SYS. WITH INEXPERIENCED COPLT; I SHOULD HAVE BEEN WATCHING/MONITORING MORE CLOSELY. SHOULD HAVE PHYSICALLY TAKEN OVER CTL OF ACFT -- DID NOT; DUE TO IOE. SUPPLEMENTAL INFO FROM ACN 373922: THE CAPT CHANGED THE RWYS; BUT FOR SOME REASON THE MAP STILL SHOWED SOME FIXES ON THE WRONG SIDE OF THE ARPT. AS I WAS TRYING TO DECIPHER WHAT THEY WERE AND WHY THEY WERE THERE; WE WERE TOLD TO DSND TO 7000 FT MSL. STILL MOSTLY PREOCCUPIED WITH THE ND MAP; I PULLED OPENED DSCNT; AND THEN ASKED THE CAPT ABOUT THE ERRONEOUS MAP INDICATIONS WHICH HE WAS ALREADY BEGINNING TO CLR OUT OF FMC. IT WAS THEN THAT WE REALIZED THAT WE HAD DSNDED BELOW 10000 FT MSL ABOVE 300 KIAS. I DISCONNECTED THE AUTOPLT AND LEVELED AT 9800 FT AND SLOWED TO 250 KIAS. I FEEL THAT THE DISTR OF MY PRE- OCCUPATION WITH THE ND MAP COUPLED WITH MY BEING USED TO THE ACFT SLOWING ON ITS OWN IN MANAGED SPD MODE; CAUSED ME TO FORGET THAT WE WERE IN SELECTED SPD MODE AND SUBSEQUENTLY NOT SLOWING THE ACFT BELOW 10000 FT MSL. ALSO A BIG FACTOR WAS FATIGUE. ALTHOUGH IT WAS THE FIRST FLT OF THE DAY; I HAD AWAKEN AT XD45 AM EASTERN WHICH IS REALLY XA45 AM PACIFIC TO MY BODY. IT WAS ALSO DIFFICULT TO FALL ASLEEP THE NIGHT BEFORE AS I AM ACCUSTOMED TO SLEEP AROUND XV30 OR XW00 PM PACIFIC; WHICH WOULD BE XA30 OR XB00 LCL EASTERN TIME; RESULTING IN ONLY A COUPLE OF HRS OF SLEEP.