The codes are in the form of two letters and/or numbers which are appended to the aircraft 's model designator , as seen in the following examples : The codes do not change if the aircraft is subsequently sold , although in some cases if an airline cancelled or sold their order before Boeing had delivered the airframe the customer code would be changed to that of the new purchaser . One such example is the order for sixteen 737-800s taken over by Qantas from American Airlines after the September 11 attacks in 2001 - these aircraft were delivered with Qantas ' 38 code rather than 23 for American
September 11 attacks
September 11 attacks
List of Boeing customer codes