Abstract: A system and method for loading cargo as cargo units in an aircraft cargo handling system having a cargo loading bay that opens laterally of the aircraft and at least one cargo stowing bay adjacent to the cargo loading bay longitudinally of the aircraft. Two self-erecting power drive units are disposed in the cargo loading bay such that the associated rollers are oriented to propel cargo units in orthogonal directions. The two power drive units in the loading bay are also disposed adjacent to each other such that, when both are in the erected position, the rollers of each unit simultaneously engage a single overlying cargo unit. The power drive units may be simultaneously placed in the erected position with the motors de-energized, such that orthogonal orientation of the de-energized drive rollers effectively prevents movement of an overlying cargo unit engaged by both rollers, whereby the cargo unit so engaged is prevented from inadvertent movement out of the loading bay.