FO OF AN AIRBUS A320; EA32; EXCEEDED SPD LIMITATION BELOW 10000 FT DURING DSCNT ARR DUE TO MISPROGRAMMING THE FMS MODE CTLING THE DECELERATION OF THE AIRSPD. THE MISTAKE WAS NOTICED JUST PRIOR TO LEVELING OFF AT THE ASSIGNED 9000 FT.

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WHILE SERVING AS PF/SIC I FAILED TO DECELERATE TO 250 KIAS BELOW 10000 FT MSL. IT IS CUSTOMARY TO UTILIZE THE A320'S MANAGED VERT NAV FUNCTION WHILE IN THE APCH ENVIRONMENT. IN THIS CIRCUMSTANCE I LEFT VERT NAV AND SELECTED THE IAS/OPEN DSCNT MODE IN ORDER TO COMPLY WITH AN ATC REQUEST TO 'KEEP YOUR SPD UP.' NOT ONLY IS VERT GUIDANCE SACRIFICED IN SELECTED SPD/OPEN DSCNT MODE; SO IS AUTOMATIC DECELERATION TO 250 KIAS. WE WERE INFORMED BY ATC TO EXPECT A RWY OTHER THAN THE ONE WE HAD PLANNED AND PROGRAMMED IN THE FMS. AS THE ACFT APCHED 10000 FT WITH CLRNC TO 9000 FT THE PNF/PIC MADE APPROPRIATE FMS CHANGES FOR THE NEW RWY AND I TOOK OUT THE CHARTED IAP IN ANTICIPATION OF A 'REBRIEF.' DESPITE MAKING THE STANDARD 'ONE TO GO' AND 'TWO TO GO' ALT AWARENESS CALLOUTS; I WAS DISTRACTED AND DID NOT NOTICE THE ACFT WAS STILL OPERATING AT 335 KIAS AS WE PASSED 10000 FT. I RECOGNIZED THE EXCESSIVE SPD PRIOR TO REACHING 9000 FT AND INITIATED A DECELERATION TO 250 KIAS. APPROX 1 1/2 MINS ELAPSED WHILE THE ACFT WAS BELOW 10000 FT AND ABOVE 250 KIAS. THIS IS A TEXTBOOK EXAMPLE HOW IMPORTANT IT IS TO CLOSELY MONITOR ADVANCED TECHNOLOGY ACFT; AND NOT TO BECOME TOO RELIANT ON THE FUNCTIONS THAT NORMALLY EASE PLT WORKLOAD. IT IS ALSO A LESSON IN DIVISION OF COCKPIT DUTIES -- BASIC CRM DICTATES 1 PLT REMAIN FOCUSED AT ALL TIMES ON FLYING THE AIRPLANE. WHILE I BELIEVE I WAS ALWAYS COGNIZANT OF ACFT POS AND ALT; I LOST TRACK OF AN IMPORTANT SITUATIONAL AWARENESS ELEMENT.