The PDUs are located in the cargo compartments of the A380. The main role of the PDUs is to provide adequate traction under all environmental conditions to move air freight pallets and containers into and out of the cargo compartment. Self-erecting PDUs are equipped with two separately acting AC servo motors. The first motor provides the necessary traction force and the second motor provides the lift function to positively engage or disengage the drive. Spring loaded PDUs are mounted between the roller tracks in order to move the pallets within the cargo compartment.