English: Boeing's advanced vehicle concept centers around the familiar blended wing body design like the X-48. What makes this design different is the placement of its Pratt & Whitney geared turbofan engines on the top of the plane's back end, flanked by two vertical tails to shield people on the ground from engine noise. The design also uses other technologies to reduce noise and drag, and long-span wings to improve fuel efficiency. This design is among those presented to NASA at the end of 2011 by companies that conducted NASA-funded studies into aircraft that could enter service in 2025.