As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW - FLT 421 - EN ROUTE DFW-SEA, SHORTLY AFTER TAKEOFF, CABIN FILLED WITH SMOKE. RETURNED DFW AND LANDED WITHOUT FURTHER INCIDENT. REPLACED APU. PERFORMED PACK BURNOUT PER MM. LEAK CHECKED GOOD. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)