(1)

In the case of combined carriage performed partly by air and partly by any other mode of carriage, the provisions of these rules shall, subject to the provisions of sub-rule (4) of rule 18, apply only to the carriage by air, provided that the carriage by air falls within the meaning of rule 1.

(2)

Nothing in these rules shall prevent the parties in the case of combined carriage from inserting in the document of air carriage conditions relating to other modes of carriage, provided that the provisions of these rules are observed with regard to carriage by air.