EgyptAir Flight 990 (MS990/MSR990) was a regularly scheduled flight from Los Angeles International Airport, United States, to Cairo International Airport, Egypt, with a stop at John F. Kennedy International Airport, New York City. On 31 October 1999, the Boeing 767 operating the route crashed into the Atlantic Ocean about 60 miles (100 km) south of Nantucket Island, Massachusetts, killing all 217 people on board. The official "probable cause" of the crash was deliberate action by the relief first officer.
As the crash occurred in international waters, the responsibility for investigating the accident fell to the Egyptian Civil Aviation Authority (ECAA) per International Civil Aviation Organization Annex 13. As the ECAA lacked the resources of the much larger American National Transportation Safety Board (NTSB), the Egyptian government asked the NTSB to handle the investigation. Two weeks after the crash, the NTSB proposed handing the investigation over to the Federal Bureau of Investigation, as the evidence suggested that a criminal act had taken place and that the crash was intentional rather than accidental. This proposal was unacceptable to the Egyptian authorities, and hence the NTSB continued to lead the investigation. As the evidence of a deliberate crash mounted, the Egyptian government reversed its earlier decision and the ECAA launched its own investigation. The two investigations came to very different conclusions: the NTSB found the crash was caused by deliberate action of the relief first officer Gameel Al-Batouti; the ECAA found the crash was caused by mechanical failure of the aircraft's elevator control system.
The Egyptian report suggested several control failure scenarios as possible causes of the crash, focusing on a possible failure of one of the right elevator's power control units. While the NTSB's report did not determine a specific reason for the relief first officer's alleged actions, their report stated the impact was "a result of the relief first officer's flight control inputs". Supporting its deliberate-act conclusion, the NTSB report determined that no mechanical failure scenario could result in aircraft movements that matched those recorded by the flight data recorder (FDR), and that even had any of the failure scenarios forwarded by the Egyptian authorities occurred, the aircraft would still have been recoverable because of the 767's redundant elevator control system.