Airwave Airlines, a recently established airline, has a frequent flyer program to compete more effectively with established airlines. To differentiate its program from those of its competitors, Airwave adopted a plan based on number of flights, rather than kilometres flown. The program offers a free return flight for every seven paid return flights taken during a three-year period. During 2013, Airwave recorded 21000 flights and revenue of $4.2 million. How should Airwave account for its frequent flyer program? Give reasons