In 2011 American Airlines loaned a new Next-Generation 737-800 to Boeing to serve as the testbed for advanced technologies testing. The FAA program known as CLEEN (Continuous Lower Energy, Emissions, and Noise) provided funding for the adaptive trailing edge on the airplane as well as some flight test costs. Other technologies on the 2012 ecoDemonstrator airplane included variable area fan nozzles, active engine vibration reduction, a regenerative fuel cell, and testing of flight trajectory optimization to enable more efficient routing for fuel savings. With fuel now the leading operating expenditure for airlines worldwide and increasingly stringent environmental regulations, improving fuel efficiency and reducing carbon and noise emissions is a top priority for the aviation sector. The flight test program allowed Boeing engineers to gather volumes of data about the viability of each technology. After testing was complete, the airplane was returned to standard configuration and delivered to American Airlines.