What was found
WHILE OPERATING IN THE CLOUDS AT 28,000 FEET MSL IN THE VICINITY OF CONVECTIVE WEATHER (TAT -3) THE AIRCRAFT EXPERIENCED 3 VERY BRIEF ERRATIC AIRSPEED ENCOUNTERS EFFECTING BOTH THE NR 1 & 2 AIRSPEED INDICATION SYSTEMS. THE NR 3 (STANDBY) SYSTEM WAS NOT OBSERVED BY THE FLIGHT CREW DUE TO THE BRIEF DURATION OF THE EVENT. THE FIRST 2 IAS DEVIATIONS CAUSED BOTH LT & RT AIRSPEED INDICATORS TO DROP 30-40 KNOTS; THE THIRD IAS DEVIATION CAUSED BOTH THE LEFT AND RIGHT AIRSPEED INDICATORS TO DROP APPROXIMATELY 50 KNOTS. THE AIRSPEED INDICATION IN ALL 3 EVENTS RECOVERED BACK TO NORMAL QUICKLY. NO OTHER AIRCRAFT SYSTEM ANOMALIES WERE NOTED. THE CREW DETERMINED THIS WAS CAUSED BY PITOT TUBE BLOCKAGE DUE TO ICE FORMATION, A KNOWN ISSUE WITHIN THE G280 FLEET. LETTER G280-MOL-20-0011, AFTER COORDINATION WITH OUR MX DEPARTMENT WE CONTINUED OPERATIONS & ACFT HAS OPERATED NORMALLY ON SUBSEQUENT FLIGHTS. THE AIRCRAFT WAS OPERATING WITHIN AFM DEFINED ICING CONDITIONS AND BOTH THE ENGINE AND WING ANTI-ICE SYSTEMS WERE SELECTED ON. THERE WAS NO VISIBLE PRECIPITATION AT THE TIME OF THE EVENT, AND THE ICE DETECTORS WERE NOT INDICATING ANY ACTUAL ICING CONDITIONS NOR WAS ICE OBSERVED ON THE AIRFRAME OR UNPROTECTED PARTS OF THE FRONT WINDOWS. AFTER THE FLIGHT, GULFSTREAM TECH OPS WAS CONTACTED TO REPORT THIS EVENT AND PROVIDE FDR DATA FOR FURTHER ANALYSIS AND REPORTING IN COMPLIANCE WITH 14 CFR 21.3.