Mich. Comp. Laws § 259.149

Sec. 149. The effectuation of the authorized purposes of a regional authority must be in all respects for the benefit of the people of the region the airport serves and in order to meet present and future state and regional needs with respect to the provision of adequate, safe, and efficient airport facilities and services to the public and to promote the economic development and well-being of this state. By performing an essential governmental function, the regional authority is not required to pay taxes or assessments of any kind or nature whatsoever on any property required or used for airport or airport facility purposes or on any rates, fees, rentals, receipts, or income at any time received by it.