Date: 201406
Local time of day: 1801-2400
Location: ZAU.ARTCC, IL
Flight conditions: IMC
Weather elements / visibility: Rain; Turbulence
Light: Daylight
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZAU
ATC / advisory: Center ZAU
Aircraft component: Pitot/Static Ice System
Component problem: Design
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Situational Awareness; Human-Machine Interface; Distraction; Confusion
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew FLC Overrode Automation; Flight Crew Took Evasive Action; Flight Crew Diverted; General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: While at cruise flight we received an 'EFIS COMP MON' caution and a boxed amber IAS on the PFD. The First Officer was the pilot flying and I was pilot not flying. I followed the QRH for those items; and when compared to the standby instruments; led us to determine that the Captain side ADC (ADC 1) had failed. With ATC we initiated a descent to FL280 in compliance with the checklist (to exit RVSM airspace). Once we were at FL280 and out of the weather; my First Officer noticed an increasing discrepancy between his airspeed and the standby airspeed. We were level; power set for cruise; and the airspeed on PFD 2 was bleeding off. At this point he stopped using the PFD and was relying on only the standby instruments. It became obvious that ADC 2 was unreliable (airspeed on PFD 2 eventually got as low as 88 KIAS) and I ran the complete ADC Failure Checklist. As per the checklist we determined the nearest suitable airport. We communicated with the Dispatcher that we were diverting due to an air data problem. We declared an emergency with ATC and received direct the field. I informed the flight attendants of our problem; that we were diverting. A PA was then made describing our problem. After we turned toward the divert airport; it appeared that ADC 2 made a recovery of some sort; and was then matching what the standby instruments were indicating. The First Officer continued using the standby instruments until a visual approach and landing were made. The approach and landing were uneventful. The Mechanic that inspected the pitot system stated that pitot systems 1 and 2 were approximately 30% full of water.The threats came in waves. The first threat was the thunderstorms that we were deviating around. After the problem began the threats were not only the ADC 1; but now ADC 2. Questions swirled in my head as to what exactly is the problem? Why are BOTH ADC's erroneous? That I must be missing something; the last threat was managing the communication with everyone - ATC; Company; flight attendants; passengers - while keeping an eye on things. I think that I may have needed to 'stop and wind the clock'; or slow down and evaluate more.

Callback: The reporter stated that the engine cowl anti-ice was ON but the wing ice was OFF because they were not accreting ice. He recalled the OAT was about -30C at FL380 before descending to FL280. He stated that an EMB-170 pilot friend had this same experience recently and he has heard of other similar instances but could not speculate about the cause.



Synopsis: A CRJ-700 experienced an apparent dual ADC failure inflight as first PFD1 then PFD2 airspeeds differed from the standby. The QRH was completed; an emergency was declared and the flight diverted but during descent the systems returned to normal. A Mechanic found both systems approximately 30% full of water.