What was found
CREW REPORTED SMOKE COMING FROM DEMISTER SYSTEM WHEN ACTIVATED. AIRCRAFT RAN UP AND VERIFIED ON GROUND. NO SMOKE COMING FROM HEATER SYSTEM WHICH IS IN PARALLEL TO DEMISTER VALVE. INSPECTED SLEEVE ASSEMBLY FOR DEMISTER AND FOUND HOSES TO BE DETERIORATED. REPLACED SLEEVE ASSEMBLY WITH NEW AND AIRCRAFT RAN UP. FURTHER MIST IN CABIN RELATED TO INSULATION PARTICLES FROM DETERIORATED HOSES. OPERATIONAL CHECK FLIGHT OF AIRCRAFT FOR 17 MINUTES AND MIST DISSIPATED WITH MINUTE PARTICLES OF INSULATION BLOWING FROM DIFFUSERS. NO FURTHER OCCURRENCE OF ISSUE REPORTED. AIRCRAFT RETURNED TO SERVICE.