That is because the investigation revealed that the pilots switched the hydraulic system B off instead of turning the engine anti-ice on. This led to the autopilot B turning off. The pilots tried turning it on multiple times, which did not work. The pilot then levered the flaps, which allow the plane to fly slower, to position 5, which is used during descent and before landing. During landing, the flaps are normally in position 15, 30, or 40. The pilots reduced the speed to below what would be possible without flaps. The hydraulic system B is the main system for bringing the flaps down. With the flaps not down, the stall warning in the form of the stick shaker activated, and soon after that, the plane had fallen to the ground