As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - CREW REPORTED STRONG FUMES IN THE CABIN. EMERGENCY DECLARED FLIGHT RETURNED ORD LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. ACCOMPLISHED PACK BURN AND REPLACED RECIRCULATION FAN FILTERS. SYSTEM GROUND CHECK NORMAL OPERATION.