ATR-42 Emergency Descent for Decompression
A First Air Avions de Transport Regional ATR-42-500, registration C-FTID performing flight 7F-852 from Yellowknife,NT to Cambridge Bay,NT (Canada) with 22 passengers and 3 crew, was enroute at FL230 about 60nm northnortheast of Yellowknife when the crew received a master warning for excess cabin altitude. The crew worked the according memory items and checklist items and performed an emergency descent to 10,000 feet. The aircraft returned to Yellowknife for a safe landing about 30 minutes after departure. The Canadian TSB reported maintenance found and replaced a damaged ground air conditioning duct check valve.