 At some stage, the concept of the flat rate was even introduced into passenger air traffic in the form of American Airlines' AAirpass.In dealing with the shipping of parcels and documents, a "flat rate for international deliveries of packet size #1" would mean that the same shipping charge (for example US$15.00) would be applicable to all packets of this size, regardless of their designated destination (country of recipient), and regardless of the quantity of their contents, i.e.whether they contained one sheet of paper or were filled to the maximum.