As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DFW INFLIGHT T1200/15JAN AFTER TAKE OFF BLUE HAZE WAS REPORTED IN CABIN. RETURNED TO DFW AND LANDED WITHOUT INCIDENT. SMOKE DISSIPATED PRIOR TO LANDING. AIRCRAFT TAKEN OUT OF SERVICE FOR EVALUATION. FOUND APU LEAKING OIL. CHANGED APU AND ACCOMPLISHED PACK BURN AND CHANGED COALESCER BAGS. SYSTEM GROUND CHECKED NORMAL OPERATION.