As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT-ORD - FLT 1640 - AFTER TAKEOFF, THE AIRCRAF WOULD NOT PRESSURIZE AND THERE WAS A LOUD NOISE AT THE AFT SERVICE DOOR. THE AIRCRAFT RETURNED TO THE FIELD AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE AFT SERVICE DOOR NOT CLOSED PROPERLY. THE DOOR WAS CLOSED PROPERLY AND THE AIRCRAFT PRESSURIZED. ALL CHECKED NORMAL. (M)