On 30 September 2017, an Airbus A380-800 en-route over Greenland suffered a sudden explosive uncontained failure of the number 4 engine shortly after thrust was increased to adjust the cruise level to FL 370. Following recovery of a crucial piece of ejected debris, the Investigation was able to determine that the failure was attributable to a specific type of fatigue failure within a titanium alloy used in the manufacture of the engine fan hub. This risk had not been identifiable during manufacture or in-service and had not been recognised by the engine manufacturer or during the engine certification process.