As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAKEOFF CABIN FILLED WITH SMOKE. FLIGHT RETURNED TO DTW. FOUND SMOKE COMING FROM APU AIR SYSTEM. PLACARD THE APU AIR INOPERATIVE PER MEL. CHECK-C 10-31-98 STL. *S/D* NO APU OIL LEAKS WERE FOUND. REPLACED THE WATER SEPARATOR BAGS AND ACCOMPLISHED DUCT BURN OUT PROCEDURES.