Regional Jet 200 ER/LR (CRJ200)
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Workload; Troubleshooting; Confusion
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; Flight Crew Landed in Emergency Condition
Aircraft; Human Factors
Due to pitot-static failure with Air Data Computer (ADC) failure detected; after following QRH for EFIS COMP MON IAS and ADC 1 failure followed by uncommanded autopilot disengage; it was difficult to see which airspeed indicator was accurate. The ISI showed a 55 knot difference than ADC 1 and 2 at 5;000' MSL; [and] ADC 1 and ADC 2 were 10-15 knots different in speed. On approach; we had to hand fly the ILS. During the approach; course deviation and correction was continuous and due to task saturation with the conditions; I [declined] when directed to go around because of the lateral deviation. We had the field in sight and determined it was safer to land than to go back into IMC with airspeed accuracy difficulties. Determined from maintenance that there was water in the pitot static [system].
Enroute we experienced rain; turbulence and arcing.  After passing through the weather we received an amber 'IAS' box located on the right side of the speed tape.  A short time later we then received an 'EFIS COMP MON' caution.  I was flying and the Captain ran the QRH.  After completing the checklist the messages came back.  We ran the checklist again.  We continued to have airspeed inconsistencies. We asked for airspeed deviations due to the inconsistencies. It appeared we had an ADC failure.  As we flew the arrival and descended for the approach the autopilot disconnected.  We tried to re-connect the autopilot; but it wouldn't engage.  We continued the ILS PRM 10 approach and as we descended on the glideslope and broke out I was left of course.  ATC instructed us to turn right heading 180.  The Captain said we were unable. We had the runway in sight and were landing due to the ADC issues.  We landed without incident.  After taxiing to the gate; the Captain called the tower to explain the reasoning for immediately landing.  We thought it was unsafe to turn and fly back into IMC conditions with the existing maintenance problems.
CRJ-200 flight crew reported experiencing system failures including airspeed indicator malfunctions that were later traced to water in the pitot static system.