The final report of the Netherlands Aviation Safety Board (NASB) concluded that the probable causes of the accident were: "The design and certification of the B-747 pylon was found to be inadequate to provide the required level of safety. Furthermore, the system [designed] to ensure structural integrity by inspection failed. This ultimately caused - probably initiated by fatigue in the inboard midspar fuse pin - the No. 3 pylon and engine to separate from the wing in such a way that the No. 4 pylon and engine were torn off, part of the leading edge of the wing was damaged and the use of several systems was lost or limited.