(1) The reports of investigations or hearings, or any part of them, may not be admitted in evidence or used for any purpose in any suit, action, or proceeding growing out of any matter referred to in the investigations or hearings, or in any report of them, except in case of criminal or other proceedings instituted by or on behalf of the department under this title.
(2) An employee of the department may not be required to testify to any fact ascertained in or information gained by reason of his official capacity.
(3) The employees of the department may not be required to testify as expert witnesses in any suit, action, or proceeding involving any aircraft or any navigation facility.