Date: February 24, 1989 Type: 747-122 Registration: N4713U Operator: United Airlines Where: Honolulu, Hawaii Report No. NTSB-AAR-90-01 Report Date: April 16, 1990 Pages: 68 Executive Summary: On February 24, 1989, United Airlines (UAL), flight 811, a Boeing 747-122 (B-747), N4713U, was being operated as a regularly scheduled flight from Los Angeles, California (LAX) to Sydney, Australia (SYD) with intermediate stops in Honolulu, Hawaii (HNL) and Aukland, New Zealand (AKL). There were 3 flightcrew, 15 flight attendants, and 337 passengers aboard the airplane. The flightcrew reported the airplane's operation to be normal during the takeoff from Honolulu, and during the initial and intermediate segments of the climb. The flightcrew observed en route thunderstorms both visually and on the airplane's weather radar, so they requested and received clearance for a deviation to the left of course from the HNL Combined Center Radar Approach Control (CERAP). The captain elected to leave the passenger seat belt sign "on." The flightcrew stated that the first indication of a problem occurred while the airplane was climbing between 22,000 and 23,000 feet at an indicated airspeed (IAS) of 300 knots. They heard a sound, described as a "thump," which shook the airplane. They said that this sound was followed immediately by a "tremendous explosion." The airplane had experienced an explosive decompression. They said that they donned their respective oxygen masks but found no oxygen available. Engines No. 3 and 4 were shutdown because of damage from foreign object ingestion. The airplane made a successful emergency landing at HNL and the occupants evacuated the airplane. Examination of the airplane revealed that the forward lower lobe cargo door had separated in flight and had caused extensive damage to the fuselage and cabin structure adjacent to the door. Nine of the passengers had been ejected from the airplane and lost at sea. The issues in this investigation centered around the design and certification of the B-747 cargo doors, and the operation and maintenance to assure the continuing airworthiness of the doors. The National Transportation Safety Board determines that the probable cause of this accident was the sudden opening of the improperly latched forward lower lobe cargo door in flight and the subsequent explosive decompression. Contributing to the cause of the accident was a deficiency in the design of the cargo door locking mechanisms, which made them susceptible to inservice damage, and which allowed the door to be unlatched, 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 the 1987 cargo door opening incident on a Pan Am B-747. The Safety Board issued three safety recommendations as a result of this investigation that addressed measures to improve the airworthiness of the B-747 cargo doors and other non-plug doors on pressurized transport category airplanes. It also issued recommendations affecting cabin safety.