As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE TO CONTROL CABIN ALTITUDE AT 24,000 FT. MANUAL OR STANDBY NO HELP. OUTFLOW VALVE INDICATED CLOSED. DESCENDED TO I0,000 AND REGAINED MANUAL CONTROL. RETURNED TO BNA. *S/D* THE CAUSE MAY HAVE BEEN A FAILURE OF THE LEFT CABIN OVER PRESSURE RELIEF VALVE. REPLACED THE OVER PRESSURE RELIEF VALVE.