Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 26; Flight Crew Total 1667; Flight Crew Type 26
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
During normal cruise; red CAS message came on; LOW PRESS; along with automatic display of of EMER Descent checklist on DU4. Cabin Pressure differential was seen as abnormally low; cabin altitude indicated 17;000 ft.; did not match pilot perception. Oxygen masked were donned according to SOP and Checklists; Pilots requested lower with ATC; leaving FL430 for FL360. at FL360; the pilots were troubleshooting the problem; and switched from ADC [Air Data Computer] #1 to ADC#2. This prompted the cabin differential pressure to rise again to a normal level. Flight was continued at FL360 to destination with no further issues.
First Officer reported ADC (Air Data Computer) #1 failure affected the cabin pressurization system; requiring a descent and a switch to #2 ADC; which restored cabin pressure control.