Within the limits of appropriations made for such purposes, the Department is authorized to purchase aircraft for the use of the Department, provided, however, that the Department shall not purchase any new or used executive aircraft unless specifically requested in the Governor’s budget and approved by the General Assembly in the Appropriations Act, and to purchase land for and to construct, maintain and improve airports, landing fields and other aviation facilities within the Commonwealth for the promotion of aviation in the interest of the public; and neither the appropriations nor any part thereof may be transferred or used for any other purpose than is specified in this section.