What was found
(CAN) SHORTLY AFTER TAKEOFF THE CREW REPORTED SMOKE IN THE CABIN AND EMERGENCY WAS DECLARED AND THE FLIGHT LANDED BELOW MAXIMUM LANDING WEIGHT. ACFT INSPECTED IAW 05-51-19 & IAW MATERIALS USED BY ADM, CONFORMING TO APPROVED FAA STANDARDS & MSDS SHEET REVIEW. ALL IN CONFORMITY. GROUND RUN C/O WITH NO FAULTS. BOTH ENGINES COMPRESSOR WASH C/O AS PRECAUTIONARY. RECIRCULATING FILTERS REPLACED IAW MSDS SHEET, LIQUID DE-ICE USED AS DE-ICE FOR RUNWAY.