As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INFLIGHT T4XG/24SEP CREW REPORTED NOXIOUS FUMES IN CABIN AND COCKPIT. COCKPIT CREW USED OXYGEN MASKS. RETURNED TO MCI AND LANDED WITHOUT INCIDENT. REPLACED AUXILIARY POWER UNIT (APU) AND PERFORMED PACK BURN OUT. SYSTEM GROUND CHECKED NORMAL OPS.