Section 302.702 - Institution of proceedings(a) Proceedings for the determination of rates of compensation for the transportation of mail may be commenced by the filing of a petition by an air carrier whose rate is to be fixed, or the U.S. Postal Service, or upon the issuance of an order by the DOT decisionmaker.(b) The petition shall set forth the rate or rates sought to be established, a statement that they are believed to be fair and reasonable, the reasons supporting the request for a change in rates, and a detailed economic justification sufficient to establish the reasonableness of the rate or rates proposed.(c) In any case where an air carrier is operating under a final mail rate uniformly applicable to an entire rate-making unit as established by the DOT decisionmaker, a petition must clearly and unequivocally challenge the rate for such entire rate-making unit and not only a part of such unit.(d) All petitions, amended petitions, and documents relating thereto shall be served upon the U.S. Postal Service by sending a copy to the Assistant General Counsel, Transportation Division, Washington, DC 20260-1124, by registered or certified mail, postpaid, prior to the filing thereof with the Department. Proof of service on the U.S. Postal Service shall consist of a statement in the document that the person filing it has served a copy as required by this section.(e) Answers to petitions shall be filed within twenty (20) days after service of the petition.