FAA Federal Aviation Regulations (FARS, 14 CFR)

(a) Each party may designate as a witness any person who is able and willing to give testimony that is relevant and material to the issues in the hearing case, subject to the limitation set forth in paragraph (b) of this section.

(b) The hearing officer may exclude testimony of witnesses that would be irrelevant, immaterial, or unduly repetitious.

(c) Any witness may be accompanied by counsel. Counsel representing a nonparty witness has no right to examine the witness or otherwise participate in the development of testimony.