Dash 8 Series Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 230; Flight Crew Type 5045
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action
Aircraft
The CAB PRESS warning light illuminated during cruise at FL200.  The First Officer (pilot flying) and I (pilot monitoring) performed the immediate action items for decompression and coordinated a rapid descent to 8;000 feet with ATC.  An emergency was not declared.  All pertinent non-normal and normal checklists were completed and the flight concluded uneventfully. The aircraft warning system worked correctly to alert us to a cabin pressure exceeding 10;000 feet with the illumination of the CAB PRESS warning light. As of yet undetermined malfunction of the air conditioning and/or pressurization computer systems.With the CAB PRESS warning light identified and the excessive cabin altitude verified; we donned our oxygen masks to 'suit up and communicate'.  The seat belt sign was turned on along with the emergency lights.  The FO (PF) then commenced a rapid descent with the condition levers at max and I announced the rapid descent with Center.  A formal emergency was not declared as there was no evidence of other malfunctions that would prevent a safe and normal flight at a lower altitude (crew decision). In accordance with the non-normal checklist; we formally unpressurized the aircraft once level at 8;000 feet. We checked in with the flight Attendant to make sure she was okay; and then updated the passengers with a reassuring PA.  Dispatch was also informed of our issue and agreed that no further action was necessary. Enroute we surveyed other related systems for additional problems with none to be found.  Our new; lower altitude also agreed with the higher terrain MORAs of the area before we continued a normal descent for an uneventful landing. To the extent that this was a hidden system malfunction; there is no way to avoid it from happening again. However; it was a great reminder to visualize and rehearse pressurization-related immediate action items for high-altitude flight in the Dash-8.
Dash 8 Captain reported he continued to destination at a lower altitude following a loss of cabin pressure.