Spirit AeroSystems manufactures aerostructures, particularly fuselages, cockpits, wing sections, engine pylons, and nacelles for commercial and military aircraft. The company was spun out of Boeing in 2005, and the firm is the largest independent supplier of aerostructures for commercial aircraft. Boeing and Airbus are the firm's primary customers—Boeing represented roughly 60% and Airbus roughly 20% of revenue in recent years. The company is highly exposed to Boeing's beleaguered 737 program, which accounts for nearly half the company's revenue.