What was found
AT FL 360 CAPTAIN`S AIRSPEED INDICATED 244, FIRST OFFICER`S 248 & STANDBY 248. BRIEFLY SPS ADV ON EICAS. AT FL 350 CAPTAIN`S AIRSPEED 231 FIRST OFFICER`S 248 & STANDBY 244. SOMEWHERE BETWEEN FL 350 & 310 CAPTAIN`S AIRSPEED & ALTITUDE DROPPED ABNORMALLY LOW. CAPTAIN`S PFD ALSO SHOWED AMBER IAS THROUGHOUT THIS TIME. INSPECTED PITOT DRAIN TUBES FOR WATER NONE FOUND. R & R NR 1 ADC IAW 124 34-15-1. PERFORMED OPERATIONAL TEST IAW 34-15-00-700-802 & PERFORMED NR 1 PITOT LEAK CHECK IAW 34-13-00-790-802. ACFT IS COMPLIANT FOR CONTINUE CAT II OPERATION.