In addition to any other penalty, when a controlled substance described in
section 1584 of this title is found on, or to have been unloaded from, an aircraft to which this subsection applies, the owner of, or individual commanding, the aircraft is liable to the Government for the penalties provided in
section 1584 of this title for each violation unless the owner or individual, by a preponderance of the evidence, demonstrates that the owner or individual did not know, and by exercising the highest degree of care and diligence, could not have known, that a controlled substance was on the aircraft.