As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAD - CREW REPORTED SMOKE IN AFT CABIN. EMERGENCY DECLARED RETURNED IAD WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. ON GROUND COULD NOT DUPLICATE. PERFORMED PNEUMATIC DUCTING BURNOUT PER MCM 21-92-12. NO DISCREPANCIES NOTED. SYSTEM GROUND CHECK NORMAL OPERATION.