Section 49O. Sections forty-nine B to forty-nine R, inclusive, shall not apply to (a) any aircraft owned and operated by or leased to and subject to the sole control of the United States or any civil or military agency of the United States or of the District of Columbia, the Commonwealth of Puerto Rico or any territory or possession of the United States; (b) any aircraft owned and operated by or leased to and subject to the sole control of any state or agency thereof or any political subdivision or municipality of any state; (c) any aircraft owned and operated by or leased to and subject to the sole control of any foreign country or any civil or military agency thereof or any political subdivision or municipality thereof; or (d) any aircraft owned or being operated by a public air carrier engaged principally in regularly scheduled inter-state or foreign air transportation for hire under either a federal certificate of public convenience and necessity or under a letter of registration or exemption order issued by the civil aeronautics board or its successor.