REPROGRAMMING OF THE FMC CAUSE MOMENTARY LOSS OF SOME DATA. FO MANAGED TO REPROGRAM WHILE CAPT WENT TO RAW DATA MOMENTARILY FOR NAV AND ACFT CTL.

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WE WERE IN THE ARR PHASE DSNDING TO 10000 MSL. ATC HAD BEEN REQUESTING HIGH SPD IN DSCNT THROUGHOUT THE ARR FOR SPACING. WE WERE INDICATING 330 KTS PASSING 12000 FT MSL AT APPROX 3500 FPM. THE FMCS WERE BEING PROGRAMMED FOR A VOR APCH TO RWY 22 LGA. AT THIS POINT WE WERE GIVEN A FREQ CHANGE TO APCH CTL. THE NEW CTLR ASKED FOR AN IMMEDIATE REDUCTION TO 250 KIAS AND 'CUT THE CORNER' WITH A DIRECT ROUTING. AS THE PNF REPROGRAMMED THE FMC; THEY WENT TO A RESYNC MODE AUTOPLT AND AUTOTHROTTLES AUTO DISCONNECTED. THE L FMC WENT BLANK; PF FD DISAPPEARED ON THE ADI AND THE HSI WENT BLANK THEN TO CLUTTER WITH WAYPOINT SYMBOLS. I SUSPECTED WE HAD OVERLOADED THE SYS AND DUMPED DATA INCLUDING THE PERFORMANCE DATA BASE (WHICH WE HAD). AS I INSTRUCTED THE PNF TO CHK THESE DATA AND SUBSEQUENTLY RELOAD BEFORE PROCEEDING AND I SET MANUAL RAW DATA WHILE HAND FLYING AND SLOWING WITH FULL SPD BRAKES; I OVERSHOT THE ALT RESTRICTION (10000 FT) BY SEVERAL HUNDRED FT. RECOVERY WAS IMMEDIATE IN CAVU CONDITIONS AND WERE BACK WITHIN ALT PARAMETERS WHEN COVERED BY THE CTLR. THE ABRUPT CHANGE IN FLT REGIME COUPLED WITH A TOTAL LOSS OF AUTOMATION AS A CRITICAL POINT CONTRIBUTED TO THE INCIDENT. IT TOOK A FEW MINS TO RESTORE EVERYTHING (WHICH WE DID ) BUT LESS THAN 30 SECONDS TO LEVEL OFF AND RESTORE MIN NAVAIDS.