As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT 576 - ON CLIMB-OUT, CREW HAD NO CONTROL OVER RT AIR MIX VALVE. VALVE WENT FULL COLD AND WAS NOT CONTROLLABLE IN MANUAL OR AUTO. FLIGHT RETURNED TO PIT WHERE LANDING WAS WITHOUT INCIDENT. MAINTENANCE REPLACED RT PACK AIR MIX VALVE. OPS CHECK, LEAK CHECK GOOD. (W)