; (2) how and when the Administration will engage airports and communities in performance-based navigation proposals; and (3) lessons learned from NextGen projects and pilot programs and how those lessons learned are being integrated into community involvement practices for future NextGen projects located in metroplexes. 177. Lead emissions (a) Study The Secretary of Transportation shall enter into appropriate arrangements with the National Academies of Sciences, Engineering, and Medicine under which the National Research Council will study aviation gasoline. (b) Contents The study shall include an assessment of— (1) existing non-leaded fuel alternatives to the aviation gasoline used by piston-powered general aviation aircraft; (2) ambient lead concentrations at and around airports where piston-powered general aviation aircraft are used