What was found
PILOT REPORTED THE WING DEICE SYSTEM WAS INOPERATIVE. AFTER VERIFYING ELEC PORTION OF SYS WAS FUNCTIONING, A GROUND OPER CHK PERFORMED. DISCOVERED VERY LITTLE FLOW GETTING TO RT SLATS, LT SLATS APPEARED TO BE GETTING SUFFICIENT HEAT, BUT BOTH SIDES ARE REQUIRED TO OPER PROPERLY TO GET A PROPER INDICATION ON PANEL. AFTER VERIFYING NO LEAKS IN AIRFRAME DUCTING, DISCOVERED THE INTERIOR WALLS OF FLEX DUCTS ATTACHED TO SLATS WERE DEBONDED AND COLLAPSING. THIS EITHER RESTRICTED/BLOCKED FLOW OF HOT AIR TO SLATS. INSP OF LT FLEX DUCTS REVEALED SAME CONDITION EXISTED, FAILURE OF THAT SIDE WAS IMMINENT. DUCTS HAVE A 3,000 HR TBO AND WERE JUST REPLACED 66.6 HRS PRIOR. SUSPECT INCORRECT MFG PROCESS. (X)