As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DEPARTED WITH PACK 1 ACM ON MEL. CLIMBING THRU FL180, TURNED ON PACK 1 AND CABIN FILLED WITH SMOKE. RETURNED TO ATL. FOUND ODOR ORIGINATING FROM APU BLEED DUE TO INTERNAL OIL LEAK. REPLACED APU AND LT PACK ACM. PERFORMED ECS DECONTAMINATION. REPLACED OZONE AND RECIRC FILTERS. OPS CHECK OK WITH NO FURTHER ODORS OR SMOKE. (4268871, 7268871, 7268666)