7199543 B1 abstract a cargo power drive unit includes a motor and at least one driver roller element coupled to the motor the power drive unit further includes a light transmitter for emitting light and a light receiver for measuring light the power drive unit measures an amount of ambient light and then measures an amount of total light after the light transmitter emits light the power drive unit then determines whether a cargo container is present based on a calculation of reflected light and the measurement of ambient light application_number US 29972205 A description one embodiment of the present invention is a pdu with an integrated sensor for detecting the presence of a uld and for sensing scrubbing fig1 illustrates an aircraft 25 and fig2 an aircraft cargo deck 26 that can be used to implement an embodiment of the present invention a generally h shaped conveyance surface 26 forms a deck of an aircraft adjacent a cargo bay loading door 23 however there are many other aircraft cargo deck configurations to which the embodiments of the invention can be implemented for example some aircraft particularly those configured primarily for the transportation of cargo without passengers have the upper passenger deck removed and an additional larger cargo deck installed other aircraft may have three or more parallel longitudinal tracks rather than the h.