NASA is soliciting proposals for studies designed to identify advanced vehicle concepts and enabling technologies for commercial airliners to fly more economically, quieter, and cleaner by 2025. NASA will select up to four teams for 12-month studies beginning in fiscal year 2011, which will define preferred concepts for advanced vehicles that can operate within the Next Generation Air Transportation System (NextGen). The concepts must incorporate technologies enabling large, twin-aisle passenger aircraft to achieve goals including 50% less fuel consumption and NOx emissions compared with today's airliners and an 80% reduction in the nuisance noise footprint around airports. After nine months of work on preferred systems' concepts, each team will be eligible to submit proposals for a subscale flight demonstrator design. NASA will select one or two concepts for 17 months of preliminary design work and risk reduction testing for completion by mid-2013.