GULFSTREAM IV ACFT DURING CLB HAD A CENTRAL AIR DATA COMPUTER AND FLT GUIDANCE COMPUTER FAULT. ALT ALERT DEFAULTED TO A HIGHER ALT AND FLC CLBED THROUGH ASSIGNED ALT BY 300 FT.

Narrative

GULFSTREAM IV ACFT DEPARTING WASHINGTON NATIONAL ARPT CLBING OUT ON A RADAR VECTOR TO THE NW. ASSIGNED 17000 FT BY CTR. WHILE CLBING THROUGH APPROX 16500 FT MSL THE #1 CADC AND #4 FLT GUIDANCE COMPUTER FAIL INDICATOR APPEARED ON THE CREW ALERTING SYS. THE AUTOPLT DISENGAGED ITSELF AND THE ALT ALERT PRESELECT WENT TO 24999 FT FROM ORIGINAL SETTING OF 17000 FT. THE ACFT WAS ALLOWED TO CLB THROUGH 17000 FT TO 17300 FT BEFORE THE ACFT WAS DSNDED BACK DOWN TO 17000 FT. IN THE MEANTIME ZDC SAID THEY NEEDED US TO GET BACK DOWN TO 17000 FT. I GUESS WE EXCEEDED OUR ASSIGNED ALT BY 300 FT ABOUT 10-15 SECONDS. OUR #1 CADC FAILURE PLAYED HAVOC WITH OUR ALT RPTING AS WE SAW IT FLUCTUATE NUMEROUS TIMES AS WE LEVELED AT 17000 FT. ZDC NEVER NOTIFIED US OF WHAT HE HAD US FOR ALT; UNTIL WE ASKED WHEN WE WERE LEVEL AT 17000 FT. HE STATED HE HAD US AT 17000 FT. WE TROUBLESHOT THE FMS SYS WITH NO RESOLUTION USING THE CHKLIST. AFTER ABOUT 5 MINS AND CLBING THROUGH 28000 FT MSL; THE #1 CENTRAL AIR DATA COMPUTER AND #1 FLT GUIDANCE COMPUTER ALERT DISAPPEARED. THE AUTOPLT SYS WAS REENGAGED AND WORKED NORMALLY; FOR THE NEXT 50 MINS. ON DSCNT TO LNDG THE PROB REAPPEARED AND A MANUAL APCH TO LNDG WAS COMPLETED AT HOME BASE. THE SYS WAS WRITTEN UP FOR REPAIR. WHEN #1 CADC AND #1 FLT GUIDANCE COMPUTER FAILED -- AUTOPLT AND AUTOTHROTTLES WERE IN OP.