Spirit AeroSystems Holdings makes commercial and military airplane components, such as fuselages, propulsion systems, wings, and underwing parts. It designs and builds aerostructures for every Boeing aircraft currently in production and provides components to Boeing's chief rival Airbus. Spirit AeroSystems claims to be the largest supplier of wing parts for Airbus' A320 aircraft and produces the majority of aerostructures for Boeing's 737. Spirit AeroSystems maintains operations in the US, the UK, and Asia; however, the US is its largest market.