Yellowstone is a Boeing Commercial Airplanes project to replace its entire civil aircraft portfolio with avanced technology aircraft. New technologies to be introduced include composite aerostructures, more electrical systems (reduction of hydraulic systems), and more fuel-efficient turbofan engines (such as the Pratt & Whitney Geared Turbofan, GEnx, the CFM International LEAP56 and the Trent 1000). The term "Yellowstone" refers to the technologies, while "Y1" through "Y3" refer to the actual aircraft.