Ala. Code § 45-37A-51.307
For the purpose of the application of the terms of the system, and for such purpose only, employees of the Birmingham Airport Authority, or for any other entity having similar jurisdiction over the Birmingham Municipal Airport, shall be deemed constructively employees of the city and the airport authority shall be deemed constructively a department of the city in the same manner and under the same terms as apply to the classified and unclassified employees of the city. The airport authority shall make or cause to be made and paid into the fund, deductions from the salaries of all of its employees who are employee members, and shall make the employer's required contributions pursuant to Section 45-37A-51.192, all under the same terms as the city employee deduction and the employer's required contributions pursuant to Section 45-37A-51.192 are made. The airport authority shall make this information available to the board of managers, the director of finance, and the custodian in the administration of the system. This provision shall not apply until a resolution of the airport authority requesting participation in the system is delivered to and approved by the board of managers. The airport authority may choose to allow its executive director and department heads, or any of them, to decline participation in the system and thereby waive and forfeit all service credit. The airport authority shall determine which of its job classifications are to be considered in the classified service for the purposes of this system.
Ala. Code § 45-37A-51.307 (1975)