Mich. Comp. Laws § 259.129

Sec. 129. Prior acquisition and operation of airport property validated. Any acquisition of property within or without the limits of any political subdivision of this state for airports, landing fields, or other aeronautical facilities, or of airport protection privileges and arrangements made for the operation of such facilities, heretofore made by any such political subdivision in any manner, together with the conveyance and acceptance thereof, is hereby legalized and made valid and effective.