14 C.F.R. § 13.117 – Conduct of investigative proceeding or deposition.

(a) The presiding officer may question witnesses.
(b) Any witness may be accompanied by counsel.
(c) Any party may be accompanied by counsel and either the party or counsel may—
1. (1) Question witnesses, provided the questions are relevant and material to the matters under investigation and would not unduly impede the progress of the investigation; and
2. (2) Make objections on the record and argue the basis for such objections.
(d) Copies of all notices or written communications sent to a party or witness must, upon request, be sent to that person's attorney of record.