49 CFR § 501.4 - Succession to Administrator.
(a) The Deputy Administrator is the “first assistant” to the Administrator for purposes of the Federal Vacancies Reform Act of 1998 (5 U.S.C. 3345-3349d) and shall, in the event the Administrator dies, resigns, or is otherwise unable to perform the functions and duties of the office, serve as the Acting Administrator, subject to the limitations established by law.
(b) In the event both the Administrator and the Deputy Administrator die, resign, and/or are otherwise unable to perform the functions and duties of their respective offices, or in the event that both positions are vacant, the following officials, subject to paragraph (c) and in the order indicated, shall serve as Acting Deputy Administrator and shall perform the functions and duties of the Administrator, except for any non-delegable statutory and/or regulatory functions and duties:
(1) The Chief Counsel;
(2) The Executive Director;
(3) Further officials as may be designated in an internal order on succession.
(c) In order to qualify for the line of succession, officials must be encumbered in their position on a permanent basis.