Ala. Code § 4-5-3
The governing body of the county issuing any such warrants or certificates may, in its discretion, pledge and use, or cause to be used, for the payment of the principal of and interest on such warrants and certificates, so much as may be necessary for said payment of any privilege, license or excise tax now or hereafter levied in such county for the purpose of construction, maintenance and operation of a county airport, or, if only a portion of such tax is levied for said purpose, so much as may be necessary for said payment of that portion of any such tax that may be now or hereafter levied for the said purpose. If more than one such pledge shall be made of the said tax, then such pledges shall take precedence in the order in which they are made unless the proceedings making such pledge shall expressly provide that such pledge shall be on a parity with or subordinate to a subsequent pledge of the said tax. All warrants and certificates for which the pledge authorized in this section may be made shall constitute preferred claims against that portion of the said tax so pledged and shall have preference over claims incurred by the county against said portion of the said tax for operation and maintenance of any such airport and claims for any other purpose whatsoever.
Ala. Code § 4-5-3 (1975)