Abstract: A roller drive unit for use in the transportation of freight containers in the hold of an aircraft. The unit comprises a drive roller, which can be retracted and which can be raised into an operating position by an electric motor, for engagement with a freight container to be transported. Sensors are distributed in a ring around the drive roller so as to be able to monitor the direction of movement of a freight container approaching the roller drive unit. A controller is connected to the sensors and to the electric motor in order that the drive roller can be raised out of its lower, retracted position into an upper, operating position or conversely, according to the signals received by the controller means from the sensors.