Narrative:

I was the captain of flight. My first officer was flying. Pre-flight through top of descent was uneventful. At top of descent we were cleared to descend from FL340 to FL240. At some point during this descent; we received an 'EFIS comp mon' caution message; accompanied with an 'IAS' amber message on each pfd. I looked at my airspeed indication; which was indicating 280 KIAS; the first officer's airspeed indicated 260 KIAS. I then said to the first officer; 'you have the airplane and the radios; I'll run the QRH procedure.' I then noticed the split getting wider; and looked at the standby airspeed indicator; which correlated closely with mine. I pointed this out to the first officer; and he seemed relieved because he said he wasn't sure if we were going to stall; or over-speed the aircraft. It was clear; based on pitch attitude; and air noise that we were nowhere near a stall. We also received a 'stall fail' caution message by this time. I did not notice the maximum airspeed split between the two airspeed indicators; but the first officer stated that at one time he saw 310 KIAS on mine; and 220 KIAS on his; a 90 knot difference. As I began to accomplish the QRH procedure in the abnormal section; the first officer reported that his airspeed trend vector accelerated through the top of the asi; and stabilized at the same airspeed as mine. All messages cleared; and since we were close to landing I put the QRH away; picked up the ATIS and began preparing to land. I called maintenance control via commercial radio and advised them of the situation; and requested maintenance meet the aircraft in at our destination. I am not sure how long this event was; and called the company the next day and advised pulling the DFDR. I do not know if this occurred. As we began maneuvering and approaching the traffic pattern; the first officer asked if I would swap his instruments over to air data computer 1 (which is in the ADC2 failure QRH procedure; where the QRH would have led us; had the situation not self-corrected; prior to subsequently closing the mach/transducer valves per the QRH procedure; had that not resolved the air speed difference). I opted not to switch the air data computer to mine; choosing instead to vigilantly cross-check the airspeed indications as we configured and landed. I briefed that if we noticed an airspeed split occurring again; I would take control of the aircraft. My thought process was that I wanted to see if the problem re-occurred and if so; report it to maintenance. We landed uneventfully. After completing the parking checklist; I called the duty chief pilot and advised him of the situation. By then the contract maintenance technician had come out to the aircraft and drained all three static systems. Only the P3 (standby) system had water in it; and it was already in the drain; so it probably would not have affected the airspeed indication (which correlated closely with mine). We were scheduled to return and the flight canceled. Overnight an avionics technician was flown in; and replaced air data computer 2. We ferried the same aircraft to our maintenance base the next day uneventfully. In retrospect (with more sleep); even though the situation appeared to have self-corrected; prudence would have dictated finish reading the QRH procedure; and switching the first officer's instruments to air data computer 1. Not switching to air data computer 1 requested was poor judgment on my part.

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Original NASA ASRS Text

Title: A CRJ-200 Air Data Computer malfunctioned during the descent. Airspeed deviations as high as 90 knots were seen along with EFIS COMP MON and STALL FAIL annunciations.

Narrative: I was the Captain of flight. My First Officer was flying. Pre-flight through top of descent was uneventful. At top of descent we were cleared to descend from FL340 to FL240. At some point during this descent; we received an 'EFIS COMP MON' caution message; accompanied with an 'IAS' amber message on each PFD. I looked at my airspeed indication; which was indicating 280 KIAS; the First Officer's airspeed indicated 260 KIAS. I then said to the First Officer; 'You have the airplane and the radios; I'll run the QRH procedure.' I then noticed the split getting wider; and looked at the standby airspeed indicator; which correlated closely with mine. I pointed this out to the First Officer; and he seemed relieved because he said he wasn't sure if we were going to stall; or over-speed the aircraft. It was clear; based on pitch attitude; and air noise that we were nowhere near a stall. We also received a 'STALL FAIL' caution message by this time. I did not notice the maximum airspeed split between the two airspeed indicators; but the First Officer stated that at one time he saw 310 KIAS on mine; and 220 KIAS on his; a 90 knot difference. As I began to accomplish the QRH procedure in the ABNORMAL section; the First Officer reported that his airspeed trend vector accelerated through the top of the ASI; and stabilized at the same airspeed as mine. All messages cleared; and since we were close to landing I put the QRH away; picked up the ATIS and began preparing to land. I called Maintenance Control via commercial radio and advised them of the situation; and requested maintenance meet the aircraft in at our destination. I am not sure how long this event was; and called the company the next day and advised pulling the DFDR. I do not know if this occurred. As we began maneuvering and approaching the traffic pattern; the First Officer asked if I would swap his instruments over to ADC 1 (which is in the ADC2 Failure QRH procedure; where the QRH would have led us; had the situation not self-corrected; prior to subsequently closing the Mach/Transducer valves per the QRH procedure; had that not resolved the air speed difference). I opted not to switch the ADC to mine; choosing instead to vigilantly cross-check the airspeed indications as we configured and landed. I briefed that if we noticed an airspeed split occurring again; I would take control of the aircraft. My thought process was that I wanted to see if the problem re-occurred and if so; report it to Maintenance. We landed uneventfully. After completing the parking checklist; I called the Duty Chief Pilot and advised him of the situation. By then the Contract Maintenance Technician had come out to the aircraft and drained all three static systems. Only the P3 (standby) system had water in it; and it was already in the drain; so it probably would not have affected the airspeed indication (which correlated closely with mine). We were scheduled to return and the flight canceled. Overnight an avionics technician was flown in; and replaced ADC 2. We ferried the same aircraft to our maintenance base the next day uneventfully. In retrospect (with more sleep); even though the situation appeared to have self-corrected; prudence would have dictated finish reading the QRH procedure; and switching the First Officer's instruments to ADC 1. Not switching to ADC 1 requested was poor judgment on my part.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.