Unique, fixed Boeing customer codes have been used by Boeing Commercial Airplanes to identify the original customer for an aircraft for all Boeing 7x7 aircraft, up to and including the Boeing 777. The codes were announced at an ICAO congress in 1956. Customer codes are not being used for the Boeing 787 Dreamliner. An example would be a Boeing 747-400 ordered by British Airways would be a Boeing 747-436 (36 being the customer code). The codes do not change if the aircraft is subsequently sold as they reflect the original configuration of the aircraft.