As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5300, IND TO STL - THE FLIGHT CREW REPORTED THAT THE PRESSURIZATION SYSTEM WOULD NOT OPERATE IN EITHER AUTO OR MANUAL MODES AND RETURNED TO IND AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE MANUAL CONTROL KNOB LOOSE. THE KNOB WAS SECURED AND THE SYSTEM OPERATED NORMALLY.