Upon the Department notifying such county boards that the petition is sufficient and that the joining of the two counties is in the public interest, each county board shall proceed with the election of Commissioners to serve as members of a Joint County Airports Commission. In determining the sufficiency of the petition, the Department shall take into consideration the relationship between the location of the principal cities and trading points in such counties and the nature of their present and future airport requirements; the nature of the terrain adjoining such cities and trading points to such needs; the effect of the joining of such counties to the then current national airport plan, the then current federal airways system, the then current State airport plan and the then current State airways system; and such other factors as under the circumstances, it regards as having an important bearing on whether such counties should be joined for airport purposes. The number of such commissioners to total nine, five of whom shall be elected by the county having the larger population, and four by the county having the lesser population. The nomination, election and qualifications of such airport commissioner, shall be as in the case of the creation of a county airport commission. Such joint commission shall be composed of two members of each county board, one “Aviation” member from each county, one “non-aviation” member from each county, and one “non-aviation” member to represent the county entitled to the fifth member, which shall come in alternate years from the smaller county.
     The commission shall be organized as is provided in the case of a county airport commission, with the chairman of the county board of the county that elected the four members of the joint commission serving as temporary presiding officer. Three of such commissioners shall serve one year, three shall serve two years and three shall serve three years. In fixing the term of office of each of the commissioners, the commissioners shall arrange that the terms shall expire in such order as the requirements of this section demand. Nothing herein shall prevent an agreement between the county boards whereby the number of commissioners elected by each county may be fixed differently, provided that the number of commissioners of each class elected by each county board is not less than one.
     Such joint commission shall have all the powers and duties as are in this act given to the county airports commission and shall exercise such powers and perform such duties as if the two counties were a single unit.