Except as provided in subsection (b) of this section, the Secretary of Transportation shall request the head of the department, agency, or instrumentality of the United States Government owning or controlling land or airspace to convey a property interest in the land or airspace to the public agency sponsoring the project or owning or controlling the airport when necessary to carry out a project under this subchapter at a public airport, to operate a public airport, or for the future development of an airport under the national plan of integrated airport systems. The head of the department, agency, or instrumentality shall decide whether the requested conveyance is consistent with the needs of the department, agency, or instrumentality and shall notify the Secretary of that decision not later than 4 months after receiving the request. If the head of the department, agency, or instrumentality decides that the requested conveyance is consistent with its needs, the head of the department, agency, or instrumentality, with the approval of the Attorney General and without cost to the Government, shall make the conveyance. A conveyance may be made only on the condition that the property interest conveyed reverts to the Government, at the option of the Secretary, to the extent it is not developed for an airport purpose or used consistently with the conveyance. Before waiving a condition that property be used for an aeronautical purpose under the preceding sentence, the Secretary must provide notice to the public not less than 30 days before waiving such condition.