Date: 201908
Local time of day: 0601-1200
Location: ZZZZ.ARTCC, FO
Flight conditions: IMC
Weather elements / visibility: Icing; 0
Light: Daylight
Aircraft: Gulfstream V / G500 / G550
Operator: Government
Operating under: Part 91
Flight plan: IFR
Flight phase: Cruise
ATC / advisory: Center ZZZZ
Aircraft component: Pitot/Static Ice System
Component problem: Malfunctioning
Reporter organization: Government
Reporter function: Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution
Contributing factors: Aircraft; Weather
Primary problem: Weather

Narrative: While cruising enroute along our planned flight path at FL430 we had experienced several hours of calm high cirrus IMC conditions. We were approximately 50 NM from the closest radar echoes of a significant and widespread storm system when we experienced a partial loss of flight control systems including autopilot/ auto-throttles and yaw damper. The system reset properly and we decided to abort our mission and look for the clearest path to our destination. Shortly thereafter the partial system failure happened again along with a loss of both P (Pilot) and CP (Co-Pilot) airspeed systems (The standby KIAS; TAS and GS appeared to be working normally at this point; however). Again we reset the system leading to a partial recovery of some flight control systems.Deciding to stay at altitude until VMC to avoid descending into inclement weather we were nearly over our destination when commencing our initial descent. At that point we once again lost our primary air data indications (CP's was reading near Mach 1 and P's was reading an impending stall condition before eventually just showing 'red X's for KCAS/ Alt and VV). Furthermore the right engine started significant surging which led to severe yaw oscillations on the aircraft. We were also getting erroneous GS indications (showing 200kt tailwind) but our TAS; standby KIAS and AOA indicator seemed correct. We had ATC provide us with updated GS readouts to ensure we were within parameters.At approximately 23;000' the air data systems returned to normal and the thicker air reduced the yaw oscillations until a safe landing could be completed normally.Our belief; in agreement with the aircraft manufacturer who completed a thorough checkout of the pitot/static systems along with electrical continuity; is that we experienced a relatively rare high ice water situation. Extremely fine particles of very dry ice particles (that do not show on radar nor trigger icing indications) led to a partial blockage of our pitot/static systems. This led to a miscompare in all 3 air data computers eventually shutting down our primary air data display information; causing our flight control malfunctions; and leading to the right engine's compressor valve cycling as designed to shed ice from the engine to prevent a compressor stall/ potential flame-out. The aircraft checklists are designed for the loss of one air data computer where redundant systems can fix a mis-compare but not for the loss of all 3.Lessons learned are avoidance of prolonged exposure to high cirrus clouds whenever possible is imperative along with backup plans to control the aircraft with whatever air data systems you can validate as still operational; and failing that; resorting to AOA readouts to ensure you are within speed parameters could be the only reliable information you have. At the end of the day; descending as soon as possible to warmer thicker air is the most likely action which will hopefully restore the air data systems and enable a normal landing.




Synopsis: G-V Captain reported Pitot Static System anomalies due to high altitude icing.