; and (2) develop a plan to mitigate the gaps identified in paragraph (1). (b) Report Not later than 1 year after the date of enactment of this Act, the Administrator shall submit to the appropriate committees of Congress a report on the actions taken to carry out the plan required by subsection (a)(2). 4108. Implementation of NextGen operational improvements (a) In general To help ensure that NextGen operational improvements are fully implemented in the midterm, the Administrator shall— (1) collaborate with air carriers and other users of the national airspace system (referred to in this section as NAS ) to develop and implement a system to systematically track the use of existing performance based navigation (referred to in this section as PBN ) procedures; (2) identify and consider other key operational improvements, including the identification of— (A) additional metroplexes for PBN projects; (B) non-metroplex PBN procedures; and (C) unused flight routes for decommissioning; (3) develop and implement guidelines for the timely inclusion of appropriate stakeholders, including airport representatives, in the planning and implementation of NextGen operational improvement efforts; and (4) ensure that NextGen planning documents inform stakeholders of how and when operational improvements are expected to achieve NextGen national goals and strategic objectives. (b) Reports Each year, as part of the submission of the NextGen Integrated Work Plan, the Administrator shall submit to the appropriate committees of Congress a report on— (1) the progress made toward implementing the requirements under subsection (a)