; (C) physical characteristics, technical standards, and classes of aircraft operating under this section; (D) trends in use, enforcement, or incidents involving unmanned aircraft systems; and (E) ensuring, to the greatest extent practicable, that updates to the operational parameters correspond to, and leverage, advances in technology. (3) Savings clause Nothing in this subsection shall be construed as expanding the authority of the Administrator to require operators of model aircraft under the exemption of this subsection to be required to seek permissive authority of the Administrator prior to operation in the national airspace system. (c) Statutory construction Nothing in this section shall be construed to limit the authority of the Administrator to pursue enforcement action against persons operating model aircraft. (d) Exceptions The Administrator may promulgate rules relating to the registration and marking of model aircraft. (e) Model aircraft defined In this section, the term model aircraft means an unmanned aircraft that— (1) is capable of sustained flight in the atmosphere