10 U.S.C. § 9017: Secretary of the Air Force: successors to duties

If the Secretary of the Air Force dies, resigns, is removed from office, is absent, or is disabled, the person who is highest on the following list, and who is not absent or disabled, shall perform the duties of the Secretary until the President, under section 3347 of title 5, directs another person to perform those duties or until the absence or disability ceases:(1) The Under Secretary of the Air Force. (2) The Assistant Secretaries of the Air Force, in the order prescribed by the Secretary of the Air Force and approved by the Secretary of Defense. (3) The General Counsel of the Department of the Air Force. (4) The Chief of Staff. (5) The Chief of Space Operations.