What was found
(CAN) AT FL200, DURING CRUISE IN ICING CONDITIONS, THE CAPTAIN`S ASI DROPPED FROM 190 KIAS TO 120 KIAS. MAINTENANCE ACTION INITIALLY HAD THE SYSTEM PURGED WITH NO MOISTURE FOUND. THEN THE CAPTAIN`S ASI WAS REPLACED, IAW AMM 34-11-33. A LEAK CHECK WAS CARRIED OUT, IAW AMM 34-11-03 AND THE SYSTEM TESTED SERVICEABLE, IAW AMM 34-11-00. AIRCRAFT CYCLES: 79090, HOURS: 64160:23. ASI S/N: 253784. (TC# 20180618003)