NTSB Probable Cause

THE SUDDEN OPENING OF THE IMPROPERLY LATCHED FORWARD LOBE CARGO DOOR IN FLIGHT AND THE SUBSEQUENT EXPLOSIVE DECOMPRESSION. CONTRIBUTING TO THE ACCIDENT WAS A DEFICIENCY IN THE DESIGN OF THE CARGO DOOR LOCKING MECHANISMS, WHICH MADE THEM SUSCEPTIBLE TO INSERVICE DAMAGE, AND WHICH ALOWED THE DOOR TO BE UNATCHED, YET TO SHOW A PROPERLY LATCHED AND LOCKED POSITION. ALSO CONTRIBUTING TO THE ACCIDENT WAS THE LACK OF PROPER MAINTENANCE AND INSPECTION OF THE CARGO DOOR BY UNITED AIRLINES, AND A LACK OF TIMELY CORRECTIVE ACTIONS BY BOEING AND THE FAA FOLLOWING A PREVIOUS DOOR OPENING INCIDENT.