Article 48 Montreal Convention
Article 48 of the Montreal Convention (Convention For the Unification of Certain Rules for International Carriage by Air) is titled Mutual Relations of Contracting and Actual Carriers. It is under Chapter V (Carriage by Air Performed by a Person other than the Contracting Carrier).
Except as provided in Article 45, nothing in this Chapter shall affect the rights and obligations of the carriers between themselves, including any right of recourse or indemnification.
See also: Article 47 Montreal Convention