Two airmail stamps from two different airmail sets are franked on this 1986 cover to Australia.
Since 1980 Cambodia has only issued two airmail sets, the first one in 1984 and the second 1986. Both share the same illustration but have different inscription, I guess the Cambodian authority was very proud of the unchanged design: how legendary to have a Ilyushin Il-62 over Angkor Wat (despite the fact that no Ilyushin Il-62 ever flew over Angkor) !
It resembles Tuva (Tannu Touva). Tuva in the 1930s and Cambodia in the 1980s were isolated and no common holiday destination. Philatelically in 1936 Tuva issued a few big sets which fully captivated young children with beautiful colour and exotic design, there included one stamp with a camel racing train, and another with a horseman watching zeppelin.
Stamps don't always give facts. There were no railway and zeppelin in Tuva, no boeing over Angkor. Illusion of advancement is always beautiful, isn't it?