As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STL INFLIGHT T1727/11NOV - FLIGHT ATTENDANTS AND PASSENGERS REPORTED STRONG AND DISTINCT ODOR OF BURNING ELECTRICAL OR INSULATION IN THE CABIN. RETURNED TO STL AND LANDED WITHOUT INCIDENT. REPLACED RIGHT HAND RECIRCULATION FAN. SYSTEM GROUND CHECKED NORMAL OPERATION.