Date: 201604
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Thunderstorm; Icing; Turbulence
Light: Dusk
Aircraft: Cessna Citation Sovereign (C680)
Operating under: Part 91
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pitot/Static Ice System
Component problem: Malfunctioning
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Diverted; Flight Crew Landed As Precaution
Contributing factors: Weather; Aircraft
Primary problem: Aircraft

Narrative: [Enroute] we determined our primary airport was not a workable option due to low ceilings and a tail wind component.  We talked with the [client] and also talked with dispatch and [selected an alternate].  We were assigned the arrival into [the alternate] at FL410.  Leaving FL410 we descended into the clouds which had thunderstorms in the area.  At approximately FL280 we got the left inboard wing anti-ice cold amber case message during our descent.  Leveling at FL260 the case message then extinguished.  Shortly after this we got the left engine control fault followed with a right engine control fault which caused a loss of the autopilot and yaw A+B.  We were able to eventually reset the autopilot and the control faults reset.  Several minutes later we again got the left and right engine control faults with a failure of the autopilot again.  We also noted the L-engine carrot for the engine power turned to amber.  The PIC noticed the airspeed indicator of the left side decreasing to 165KTS in the descent which didn't seem right; then we heard the overspeed clacker indicating an overspeed condition of the aircraft.  We both then noted the overspeed condition on the right side along with the standby instruments.  I then noted a slow decrease in airspeed on the left side all the way down to 30KTS.  I transferred controls to the right seat pilot where the SIC stopped the rate of descent to level attitude.  At this time we noted VFR conditions underneath us to the ground.  We asked the controller if we had an airport underneath us and were told that [a suitable airport] was about 10 miles away with visual conditions. We decided to [request] priority handling to the airport.  We then noted that the AHRS was totally inoperative with a red X on all the left instruments leaving me without any airspeed or any other reference data on the left side. The Controller then vectored us to a right downwind to the uncontrolled airport without any further incidence.  This reminds me of the simulator training we had recently which simulated [another air carrier] incident which had wrong airspeed indications due to severe icing conditions.  We were fortunate this didn't affect the right side or standby instruments and it was also fortunate we had VFR conditions underneath us as [our first alternate] was at minimums and 30 minutes away.


Second narrative: I am very thankful for the sim training we had that covered icing/incorrect indications from Air Data Computer information. I quickly felt very confident of our assessment that the anti-ice/protection systems were unable to handle the conditions and [we took] corrective actions in response to the situation.


Synopsis: CE-680 flight crew reported diverting to an alternate after noting system multiple anomalies associated with probable pitot/static icing.