Combi aircraft in commercial aviation are aircraft that can be used to carry either passengers as an airliner, or cargo as a freighter, and may have a partition in the aircraft cabin to allow both uses at the same time in a mixed passenger/freight combination. The name combi comes from the word combination. The concept previously existed in railroading, as a passenger car that contained a separate compartment for mail and/or baggage. Combi aircraft typically feature an oversized cargo door, as well as tracks on the cabin floor to allow the seats to be added or removed quickly. Typically, configured for both passenger and cargo duty, the passenger compartment is pressurized to a higher pressure, to prevent potential fumes from cargo entering the passenger area. Airlines Northwest Airlines In 1963, Northwest Airlines operated a domestic and International routing with a Douglas DC-7C four engine propeller aircraft between New York Idlewild Airport (which would subsequently be renamed JFK Airport) and Tokyo that was configured to transport a mixed passenger/cargo load. The round trip routing for this flight which was operated once a week was New York-Chicago-Seattle-Anchorage-Tokyo. The DC-7C was configured with all economy seating in the passenger cabin. By 1966, Northwest was operating jet combi service with Boeing 707-320C aircraft between the U.S. and Asia. Braniff International In 1968, Braniff International was flying Boeing 727-100QC ("Quick Change") jetliners in a configuration that facilitated the transportation of palletized freight containers as well as 51 passengers in an all-economy-class cabin in scheduled airline operations. According to a Braniff system timetable dated July 1, 1968, the airline was operating weekday "red eye flights" with round trip services at night with its B727 combi aircraft on the following routings: New York (JFK) - Washington, D.C. (IAD) - Nashville (BNA) - Memphis (MEM) - Dallas Love Field (DAL); Seattle (SEA) - Portland (PDX) - Dallas Love Field (DAL); and Denver (DEN) - Dallas Love Field (DAL). The freight pallets were loaded in the front section of the aircraft by forklift via a large cargo door located on the side of the fuselage aft of the flight deck while passengers boarded and deplaned via the integral air stairs located at the rear underneath the trijet's engines. These aircraft could also be quickly changed to fly either all cargo or all passenger operations and Braniff flew the B727QC in both configurations besides operating in a mixed passenger/freight combi