In City of Cheyenne v. Bd. of County Comm'rs of the County of Laramie, 484 P.2d 706 (Wyo. 1971) the Court noted that many authorities do apply a tort liability test and find a purpose proprietary if income is generated; however, we decided that generating income is not controlling, and merely renting a building to a lessee engaged in a profit-making venture is not a use for a nongovernmental purpose. 484 P.2d at 709. There, the Court decided that because the buildings were necessary or essential facilities to the efficient operation and maintenance of the airport, the improvements were not subject to taxation. Id.