Article 26 Montreal Convention
Article 26 of the Montreal Convention (Convention For the Unification of Certain Rules for International Carriage by Air) is titled Invalidity of Contractual Provisions. It is under Chapter III (Liability of the Carrier and Extent of Compensation for Damage).
Any provision tending to relieve the carrier of liability or to fix a lower limit than that which is laid down in this Convention shall be null and void, but the nullity of any such provision does not involve the nullity of the whole contract, which shall remain subject to the provisions of this Convention.
See also: Article 25 Montreal Convention