A combine harvester comprising threshing apparatus, a grain pan and a cleaning unit is provided. The grain pan is arranged to collect a grain/chaff stream from the threshing apparatus and is driven in an oscillating manner to convey the collected grain/chaff stream rearwardly to a rear edge from where the grain/chaff stream falls under gravity into the cleaning unit. The cleaning unit comprises a fan unit for generating a first cleaning airstream which is directed under the grain pan and through the grain/chaff stream falling from said rear edge. The combine harvester further comprises means to generate a second cleaning airstream vented above the grain pan.
