In order to reasonably lay out the fleet and further save the cost of human resources of airlines, CAAC recently revised the Advisory Circular on Cross Crew Qualification and Mixed Fleet Flying (AC-121FS-025). The newly-promulgated Advisory Circular on Shortened Transition Course and Mixed Fleet Flying (hereafter referred to as the Advisory Circular) will be applied to large-scale mixed fleet flying between two similar aircraft types, aiming to improve the economic performance of airlines while ensuring safety.