A CL65 FLC LOSES THE #1 AIR DATA COMPUTER. WHILE SORTING OUT THE PROB THE TCASII RA CREATES THE NEED OF AN ALTDEV FOR THE CREW.

Narrative

OPERATING FLT CVG-ATU; CRUISING AT FL310. CAPT'S LEG. HIS AIRSPD STARTED FLUCTUATING WILDLY. THE HIGH SPD WARNING TICKER WENT OFF CONSTANTLY. HE REDUCED PWR TO STOP THE WARNING. AT ONE POINT; HIS READ 400 KTS; MINE READ 260 KTS. THE ALT TAPE ALSO FLUCTUATED. I NOTIFIED ATC QUICKLY TO LET THEM KNOW OUR ALT AND AIRSPD WERE INACCURATE. TOLD THEM IT WAS AN AIR DATA ATTITUDE/HDG REFER SYS PROB. A FEW MINS LATER WE GOT A TA TO CLB. THE RA SAID CLB AND WE DID. SAW ACFT ABOUT 4-5 MI AWAY AND 1000 FT VERT. WE NEVER MADE ABRUPT CHANGES TO AVOID THE OTHER ACFT. WE PROBABLY FLUCTUATED 300-400 FT OFF OUR ALT OF FL310; OUR BEST GUESS. BY THIS TIME THE CAPT'S AIRSPD AND ALT TAPE DISAPPEARED. THE STANDBY ALT AT FL310 NORMALLY READS 300- 400 FT HIGH. WE WENT THROUGH THE QRH AND FIGURED OUT THE PROB WAS THE AIR DATA COMPUTER. SWITCHED TO AIR DATA #2. WE BEGAN OUR DSCNT TO ATW; AND LANDED UNEVENTFULLY. CALLED MAINT AND ATC BY THE PHONE NUMBER THEY GAVE US ENRTE. ATC WAS CONCERNED ABOUT THE OTHER ACFT. IT WAS NOT A CLOSE CALL. THAT SEEMED TO BE HER MAIN CONCERN. HE SAID THE SAME THING MAY HAPPEN ON THE NEXT LEG OR 3 MONTHS FROM NOW; OR MAYBE NEVER. MAINT CAME OUT TO THE ACFT. A WRITE-UP WAS ENTERED IN THE BOOK.