Ala. Code § 4-3-18
The proceeds derived from the sale of any bonds (other than refunding bonds) may be used only to pay the cost of acquiring, constructing, improving, enlarging and equipping the airport, facilities or property with respect to which they were issued, as may be specified in the proceedings in which the bonds are authorized to be issued. Such cost shall be deemed to include the following: the cost of any land forming a part of such airport, facilities or property; the cost of labor, material and supplies used in any such construction, improvement or enlargement, including architects' and engineers' fees and the cost of preparing contract documents and advertising for bids; the purchase price of and the cost of installing equipment for the airport, facilities or property; the cost of landscaping the lands forming a part of such airport, facilities or property and of constructing and installing roads, sidewalks, curbs, gutters, utilities and parking places in connection with the airport, facilities or property; legal, fiscal and recording fees and expenses incurred in connection with the authorization, sale and issuance of the bonds issued in connection with such airport, facilities or property; and interest on said bonds for a reasonable period prior to and during the time required for such construction and equipment and for not exceeding 18 months after completion of such construction and equipment. If any of the proceeds derived from the sale of said bonds remain undisbursed after completion of such work and payment of all of the said costs and expenses, such balance shall be used for retirement of the principal of the bonds of the same issue.
Ala. Code § 4-3-18 (1975)