As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 3855 -ATB/FUMES- RETURNED ATL DUE TO FUMES IN THE COCKPIT AND CABIN DURING CLIMB. CORRECTIVE ACTION: PERFORMED ENGINE RUNS AT VARIOUS POWER SETTINGS AND PERFORMED AIR SAMPLES DURING ENTIRE RUN. ALL READINGS WERE LOW. REPLACED RECIRCULATION FILTERS.