14 CFR 221.140 - Method of giving concurrence.
(a) A concurrence prepared in a manner acceptable to the Office of International Aviation shall be used by a carrier to give authority to another carrier to issue and file with the Department tariffs which contain joint fares or charges, including provisions governing such fares or charges, applying to, from, or via points served by the carrier giving the concurrence. A concurrence shall not be used as authority to file joint fares or charges in which the carrier to whom the concurrence is given does not participate, and it shall not be used as authority to file local fares or charges.
(b) Number of copies. Each concurrence shall be prepared in triplicate. The original of each concurrence shall be filed with the Department, the duplicate thereof shall be given to the carrier in whose favor the concurrence is issued, and the third copy shall be retained by the carrier who issued the concurrence.
(c) Conflicting authority to be avoided. Care should be taken to avoid giving authority to two or more carriers which, if used, would result in conflicting or duplicate tariff provisions.