Section 51E. In any city or town in which an airport is established under section fifty-one D, or under any other provision of law, there shall be established a board consisting of an odd number of members not less than three nor more than eleven in number, to be called the airport commission, which shall have the custody, care and management of the municipal airport of said city or town. Of the members appointed at least one shall be a person having experience in aeronautics. An airport commission may be established as herein provided in any city or town for the purpose of establishing an airport therein. Except as provided otherwise in any special law, enacted prior to January first, nineteen hundred and forty-seven, relating to an airport commission in any city or town, the members of the airport commission shall be appointed, in cities, by the mayor with the approval of the city council, and in towns by the selectmen. In the initial appointment of the members of such an airport commission, their terms shall be so arranged that one third of the members, as nearly as possible, will expire each year; and thereafter when the term of any member expires his successor shall be appointed to serve for the term of three years and, in each instance, until the qualification of his successor. Vacancies in the commission shall be filled for the unexpired term by the appointing authority. The members of said airport commission shall annually choose one of their members as chairman. The airport commission may appoint an airport manager who shall be qualified by general management experience and aeronautical knowledge and shall be the executive officer of said commission, and may also appoint an assistant airport manager who shall be qualified as aforesaid. Neither the airport manager nor the assistant airport manager shall be subject to chapter thirty-one. The assistant airport manager shall act in place of the airport manager at such times and under such conditions as the airport commission may direct. The airport manager, and the assistant airport manager when acting in place of the airport manager under the direction of the airport commission, shall be responsible to said commission for the proper maintenance and operation of such airport and of all facilities under his supervision. Subject to appropriation, said commission shall appoint such other officers and employees as its work may require and shall fix the salaries of all officers and employees appointed or employed by it.