The 747-400F (Freighter) is an all-freight version of the successful 747-400 model. While using the updated systems and wing design of the passenger version, it features the original short upper deck found on the classic 747s in order to save weight. The model's first flight was in 1993, and it entered service with Cargolux in the same year. Major customers have included Atlas Air, Cargolux, Cathay Pacific, China Airlines, Korean Air, Nippon Cargo Airlines, Polar Air Cargo, and Singapore Airlines. The −400F can be easily distinguished from the passenger −400 by its shorter upper-deck hump and lack of windows along the main deck. The aircraft is fitted with a PW4000 engine.