As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFT CARGO DOOR MASTER CAUTION IN FLIGHT AT 3000 FT QRH 2 PROCEDURES COMPLETED. UNABLE TO DETERMINE IF AIRCRAFT WAS PRESSURIZED NORMALLY. AFTER LANDING IN DULLES CRASH FIRE RESCUE INSPECTION DETERMINED DOOR WAS STILL CLOSED. AS PER TELECON WITH MXC DEFERRED AFT CARGO DOOR IND ON OCN 70081319 PER MEL 52-70-04B CAT C.