Section 604.20 - Effect of an advisory opinion(a) An advisory opinion represents the formal position of FTA on a matter, and except as provided in § 604.25 of this subpart, obligates the agency to follow it until it is amended or revoked.(b) An advisory opinion may be used in administrative or court proceedings to illustrate acceptable and unacceptable procedures or standards, but not as a legal requirement and is limited to the factual circumstances described in the request for an advisory opinion. The Chief Counsel's advisory opinion shall not be binding upon a Presiding Official conducting a proceeding under subpart I of this part.(c) A statement made or advice provided by an FTA employee constitutes an advisory opinion only if it is issued in writing under this section. A statement or advice given by an FTA employee orally, or given in writing, but not under this section, is an informal communication that represents the best judgment of that employee at the time but does not constitute an advisory opinion, does not necessarily represent the formal position of FTA, and does not bind or otherwise obligate or commit the agency to the views expressed.