Abstract: A retracting power drive unit for an aircraft cargo handling system wherein a power driven wheel or tire engages the undersurface of a cargo container for horizontally moving the cargo in different directions. The directional positioning mechanism of the power drive unit retains the tire in partial frictional engagement with the undersurface of the cargo container while the directional movement of cargo container is changed in order that the cargo container is retained under positive control at all times. This is necessary when loading or unloading an aircraft on a pitching and rolling aircraft carrier deck, or where the floor of the cargo compartment is unlevel. The operation of retracting and changing the directional orientation of the powered wheel drive unit, relies on the interaction of a dual cam system which provides for a two-step controlled lowering of the powered wheel, in addition to a rotation thereof about a vertical axis, for a change in the directional movement of the cargo container.