; and (2) the operator of the stage 2 aircraft operates not more than 10 flights per month using that aircraft. (b) Termination The pilot program shall terminate on the earlier of— (1) the date that is 10 years after the date of the enactment of this Act; or (2) the date on which the Administrator determines that no stage 2 aircraft remain in service. (c) Definitions In this section: (1) Medium hub airport; nonhub airport The terms medium hub airport and nonhub airport have the meanings given those terms in section 40102 of title 49, United States Code. (2) Stage 2 aircraft The term stage 2 aircraft has the meaning given the term stage 2 airplane in section 91.851 of title 14, Code of Federal Regulations (as in effect on the day before the date of the enactment of this Act). 173. Alternative airplane noise metric evaluation deadline Not later than 1 year after the date of enactment of this Act, the Administrator of the Federal Aviation Administration shall complete the ongoing evaluation of alternative metrics to the current Day Night Level (DNL) 65 standard. 174. Updating airport noise exposure maps Section 47503(b) of title 49, United States Code, is amended to read as follows: (b) Revised maps (1) In general An airport operator that submits a noise exposure map under subsection (a) shall submit a revised map to the Secretary if, in an area surrounding an airport, a change in the operation of the airport would establish a substantial new noncompatible use, or would significantly reduce noise over existing noncompatible uses, that is not reflected in either the existing conditions map or forecast map currently on file with the Federal Aviation Administration. (2) Timing A submission under paragraph (1) shall be required only if the relevant change in the operation of the airport occurs during— (A) the forecast period of the applicable noise exposure map submitted by an airport operator under subsection (a)