As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT - FLT NR 1567 - AIRCRAFT DISPATCHED WITH MEL 21-1A ON RIGHT PACK. COULD NOT PRESSURIZE AFTER TAKEOFF. RETURNED TO PIT AND LANDED WITHOUT INCIDENT. MAINTENANCE PRESSURIZED AIRCRAFT TO 6 PSID. NO DEFECTS NOTED. RELEASED AIRCRAFT FOR SERVICE. (M)