As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL/IND - FLT 510 - DURING CRUISE, THE CABIN ALTITUDE ALERT DISPLAYED AND THE PRESSURIZATION SYSTEM WAS UNCONTROLLABLE. THE AIRCRAFT DIVERTED TO PIT AND LANDED WITHOUT INCIDENT. MAINTENANCE PERFORMED FUSELAGE LEAK TEST, CHECKED THE OUTFLOW VALVE OPERATION, AND A FUSELAGE LEAK DOWN TEST. ALL CHECKED OK. THE NR 1 PRESSURIZATION CONTROLLER WAS REPLACED. (X)