As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 3750-FUME/ODOR- NOTED BRIEFLY ON DEPARTURE. RETURNED ON DESCENT. CREW DONNED MASKS FOR THE REMAINDER OF THE FLIGHT. CORRECTIVE ACTION: C/W NO-GO-ODI INSPECTION TASKS. REPLACED CRACKED LEFT PACK CONDENSER AND RECIRCULATION FAN FILTERS.