Date: 201303
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: Icing; Turbulence
Light: Daylight
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Data Computer
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Situational Awareness; Workload; Human-Machine Interface
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 Landed As Precaution; Flight Crew Took Evasive Action; General Declared Emergency; General Maintenance Action
Contributing factors: Aircraft; Weather
Primary problem: Ambiguous

Narrative: Cruise at FL360 was in VMC 1;000 FT above a solid cloud deck. Given lower by ATC we descended into IMC at approximately FL350. A minute or so into the IMC my airspeed indication began to decay. No ice was accumulating on the aircraft; including the wiper nuts. Quickly [we] got an 'EFIS COMP MON' message. Crossed referenced the First Officer's and STBY speed to verify. I pulled the QRH and the First Officer's airspeed began to decay. I told him to only reference the STBY for airspeed. Things quickly began to get worse as all ADC information began falling off line. Every failure was somewhat slow and one at a time. The autopilot began wagging the wings very firmly about 10 degrees or so back and forth. I told the First Officer to disconnect it and hand fly while I figure this out. The flight attendants tried to call but I didn't answer. Aircraft control was paramount. We lost everything provided by the air data computers. An emergency was declared with Center. Altitude/Airspeed/Heading were all red boxes on both PFDs. A cascade of amber caution messages consistent with complete ADC failure came onto ED1. STALL FAIL/RUD LIMITER/MACH TRIM/AUTO PRESS/WINDSHEAR FAIL/GPWS FAIL/L-R FADEC FAULT 2 SPLR-STAB FAULT. The First Officer was flying the aircraft referencing the STBY only in a descent in rough air IMC. As the aircraft descended the First Officer said 'I need help' so I stopped everything to help maintain control of the aircraft. The airspeed on the STBY began to decay and in natural response the First Officer decreased pitch. The roar of air over the airframe caused me to query ATC. At an indicated airspeed somewhere around 100 KTS; ATC said we were going 320 into a known headwind. We ended up with no airspeed indications that were reliable. The STBY was at 0. We were flying solely on pitch and power in an emergency descent at high altitude in rough IMC. I got back to the flight attendants and told them we were in an emergency but everything is under control and we'd update if necessary. The passengers were never notified. Not knowing what's reliable; he concentrated on keeping the wings level and a steady pitch while I constantly scanned/cross referenced the instruments and provided verbal commands to maintain control of the aircraft. I asked ATC for any VFR and he said the closest was 20 minutes away. I told him we could take a gentle turn toward a nearby airport as weather was improving. As we descended somewhere around 10-12 thousand feet the ADC's came alive and although the information was crosschecked inaccurate; it was coming back. Most of the amber caution messages self-cleared. At 7;000 FT we finally saw the Earth. Visibility was poor but enough to keep the aircraft under control should all fail again. The lower we got the more 'matched' the PFD's became. Somewhere during the final descent/approach the autopilot was re-engaged during the final few miles; although closely monitored. The First Officer hand flew the ILS. At one point we were indicating 210 KTS while ATC showed us at 270. Using pitch/power/performance the First Officer flew the ILS perfectly to touchdown. A normal taxi/deplaning took place just as a large thunderstorm closed the ramp. The aircraft was de-powered and circuit breakers for the FDR system were pulled followed by a subsequent write up. Additionally-this report is provided to the best of my knowledge at the time of submittal. Some things may have occurred which I cannot recall due to the high stress level of the situation.Threats: IMC/invalid-failed instruments undesired aircraft state: Probable airframe over speed. I would suggest training pitch/power descents from high altitude. Pray this never happens again.

Callback: The reporter's first comments to this analyst during callback was 'Did you ever wonder what your last radio call would sound like?' He was uncertain what the aircraft's state was during the time all pitot static data was lost which affected the aircraft's controllability. The aircraft had overnighted at a station in heavy rain then flown by this crew on a short 45 minute flight followed by a longer 2 hour 45 minute flight during which the anomalies occurred. The only data available to the crew was standby altitude and the reporter who was previously an instructor on this aircraft was thoroughly confused by the loss of standby information. At one point the only action taken by the crew was to remain wings level in a descent because they did not know what would result if a change in the aircraft's state was made. After landing the crew was removed from flight status and the aircraft given to Maintenance who cleaned the aircraft pitot static system; blew out the ADC and reset the computers. The aircraft was then flown to a major maintenance base for further examination. Maintenance suspected accumulated moisture in the pitot static system; which subsequently froze on the long leg; was the cause of this event.



Synopsis: A CRJ-700 descended into IMC at about FL350 and lost all air data computer information; resulting in the loss of numerous systems and leading to an airframe overspeed. A diversion was made to a nearby airport where all systems returned to normal in VMC conditions.