Aviation expert Geoffrey Thomas said such an incident was “extremely unusual”. “A stick shaker is an extremely rare event, and very, very serious,” he said. This is an “aero-¬dynamic stall” which occurs when “the angle of attack of the wing increases beyond a point such that the lift begins to decrease”. “The airflow over the wing begins to separate and it breaks up. There is a sudden decrease in altitude, which is why some passengers may have been injured.” In this case, the incident may have been an auto¬pilot malfunction. The flight crew disconnected the autopilot and commanded the aircraft in response. The Australian Transport Safety Bureau has opened a serious incident investigation.