國際航空貨物運送中，運送人常會因為某種特定原因在某運送段改用其他運送工具替代運送，這種情形，對託運人或受貨人來說，並不陌生。實際上，國際航空貨物運送在前後兩段機場外之運送雖亦是使用航空器以外的運送工具，如果的替代運送」的涵義內，欲定航空運送人之責任，只要依據華沙公約18條第三項之規定即可。而國際航空貨物運送，與運送人在某運送段所為之替代運送，本質上係屬「複合運送」，如何航空運送人之責任，在運送法上是個困難的問題，其中，符合契約約定之航空貨物運送的替代運送及違反契約約定之航空貨物運送的替代運送又分別須區分為損害地明知與損害地不知的情，更增添問題的複雜性。

Besides aircrafts, carriers often use other means of transport in the international air cargo carriage. Such a situation of operation is familiar to both consignors and consignees. Usually the inevitable use of non-aircrafts for the purposes of loading, transit, and discharge is viewed as the extension of air transport and not as its substitution, so here we must apply article 18 section 3 of the Warsaw convention to make certain of the liability of the liability of the air carrier. In transportation law what is known as “multimodal transport” includes both the international air cargo carriage and its substitution. How to ascertain the liability of air carrier in various cases is a difficult legal problem, because the liability depends on whether we know at which transport section the damage has happened, and whether the transportation is done as contracted.