What was found
AFTER TAKEOFF SMOKE BEGAN COMING OUT OF THE VENTS IN THE COCKPIT AND AT ROW 8 IN THE CABIN. THE SMOKE CONTINUED UNTIL THE AC WAS ON THE GROUND. AIRCRAFT HAS A BURNING SMELL IN CABIN AND COCKPIT. CAME BACK AROUND AND LANDED WITHOUT INCIDENT. LANDING WEIGHT 45,000 LBS. RAN AIRCRAFT WITH APU AIR AND ENGINE AIR. ENGINE AIR RUNS CLEAR. APU AIR IS CONTAMINATED. SUSPECT DEICE FLUID. SEE 238190/4 FOR MEL.