 Typically, overwing evacuation slides are not designed for use in ditching situations as they cannot be detached.and will not operate, as the system is disabled by the aspirators on the slide taking in water.Aircraft where there is no over-wing slide, such as the Embraer 190, 717, and 737 do not require them by regulation because when the flaps are fully lowered, they are low enough to the ground to meet the requirement.