Aviation safety experts have continued theorizing about what caused the March 21 crash of a China Eastern Boeing 737-800 that killed all 132 people on board. Preliminary findings from American authorities investigating the crash may have an answer, suggesting that the aircraft was put into an intentional nosedive, falling from the sky and crashing into the Guangxi mountains in southern China.The black box, or flight data recorder, was retrieved from the wreckage and the analysis of its information helped authorities determine that the cause appears to have been human input, reports The Wall Street Journal, which cites unnamed sources familiar with the investigation."The plane did what it was told to do by someone in the cockpit," the source told The Wall Street Journal.Data from flight tracking website FlightRadar24 showed the aircraft sharply dropped from an altitude of 29,100 feet to 3,225 feet in three minutes before flight information stopped. Chinese officials involved in the crash investigation have yet to flag any mechanical or flight problems with the aircraft.According to the Civil Aviation Administration of China, the Boeing 737-800 lost contact over Wuxhou city, losing height rapidly from cruising altitude before plummeting to the ground."That kind of vertical dive, without a radio call of any kind from the flightcrew, could clearly indicate a human activity to make that happen," Former NTSB member and aviation safety consultant John Goglia told FlightGlobal last month. "Nobody can come up with a mechanical failure mode that would make the airplane behave the way it did."Footage that has circulated of Flight MU3735 shows the aircraft plummeting vertically from the sky. The cause of the crash has not been officially determined, but these findings suggest that the nosedive could have been caused by one of the pilots, or another passenger breaking into the cockpit.China Eastern has previously said the pilot flying the aircraft was in good physical, emotional, and financial health. However, Chinese officials have also noted that flight MU3735 did not send out any distress signals and air traffic control did not indicate anything out of the ordinary about the crash.Chinese officials have completed the initial investigative report for the crash, but have not released it in full.