49 CFR § 831.57 - Representation during an interview.
(a) Any person interviewed in any manner by the NTSB has the right to be accompanied during the interview by no more than one representative of the witness's choosing. The representative -
(1) May be an attorney;
(2) May provide support and counsel to the witness;
(3) May not supplement the witness's testimony; and
(4) May not advocate for the interests of a witness's other affiliations.
(b) An investigator conducting the interview may take any necessary action (including removal of the representative from the interview) to ensure a witness's representative acts in accordance with the provisions of paragraph (a) of this section during the interview, and to prevent conduct that may be disruptive to the interview.