; funding Section 47124(b)(3)(E) is amended to read as follows: (E) Funding Of the amounts appropriated under section 106(k)(1), such sums as may be necessary may be used to carry out this paragraph. . (c) Cap on Federal share of cost of construction Section 47124(b)(4)(C) is amended by striking $2,000,000 and inserting $4,000,000 . (d) Cost benefit ratio revision Section 47124 is amended by adding at the end the following: (d) Cost benefit ratios (1) Contract air traffic control tower program at cost-share airports Beginning on the date of enactment of the Federal Aviation Administration Reauthorization Act of 2017 , if an air traffic control tower is operating under the Cost-share Program, the Secretary shall annually calculate a new benefit-to-cost ratio for the tower. (2) Contract tower program at non-cost-share airports Beginning on the date of enactment of the Federal Aviation Administration Reauthorization Act of 2017 , if a tower is operating under the Contract Tower Program and continued under subsection (b)(1), the Secretary shall not calculate a new benefit-to-cost ratio for the tower unless the annual aircraft traffic at the airport where the tower is located decreases by more than 25 percent from the previous year or by more than 60 percent over a 3-year period. (3) Considerations In establishing a benefit-to-cost ratio under paragraph (1) or paragraph (2), the Secretary may consider only the following costs: (A) The Federal Aviation Administration's actual cost of wages and benefits of personnel working at the tower. (B) The Federal Aviation Administration's actual telecommunications costs of the tower. (C) Relocation and replacement costs of equipment of the Federal Aviation Administration associated with the tower, if paid for by the Federal Aviation Administration. (D) Logistics, such as direct costs associated with establishing or updating the tower's interface with other systems and equipment of the Federal Aviation Administration, if paid for by the Federal Aviation Administration. (4)