What was found
FL330, ACFT ABRUPTLY STARTED DESCENDING. CAPTAIN'S IAS DROPPED TO 80 KTS, F/O READ OVER 300 IN DESCENT DISCONNECTED AP AND LEVELED ACFT USING STANDBY ADI AND AIRSPEED INDICATOR. ECAM MESSAGE INDICATING TAS AND ADC DISAGREED. ALSO NAV ADC FAILURE INDICATED ON ECAM. PERFORMED AUTOFLIGHT, OPS TEST IAW AMM 22-00-00-0501, FOUND "ADS 1 FLAG " ON MTP FAILURE RECORD. R & R NR 1 ADC IAW AMM 34-11-08-02-130A . BITE TEST CKS GOOD.