What was found
SMOKE AND FUMES EVIDENT IN CABIN AND COCKPIT. SIC INVESTIGATED, SMOKE AND FUMES SEEMED TO BE COMING FROM ENVIROMENTAL SYSTEM EVENLY THROUGH AIRCRAFT. RETURNED FOR LANDING. FIRE DEPARTMENT GREETED US, NO ABNORMALITIES FOUND WITH FLIR. PER MCC REQUEST, RAN ENGINES TO BURN OUT DUCTS OF ANY REMAINING OIL SMALL, COCKPIT AND CABLN ARE CLEARED OUT OF ANY REMAINING OIL SMELL, REF GL-6000 MM, 21•52•00 & POH. APU NEEDS REPLACEMENT DUE TO COMPRESSOR SEAL OIL LEAK, SEE BARCODE # T2PL6DOOB17TY, PLACED ON MEL 49-10-01. MAINTENANCE PROCEDURES COMPLIED WITH.