Here is a great combination of 2 special aspects to this cover! It is a First Day Cover of Canal Zone 141, the 10c Barro Colorado "Coati-mundi"  issue of 1948, postmarked at Balboa Heights April 17, 1948, and addressed to a Mr CT Cheng,  4 Bongkaran Street, Soerabaya (also Surabaya) Java, Dutch East Indies. It is backstamped with both an indistinct DEI receiving cancel at a town ending in "-RUM" and at Soerabaya on June 9, 1948, and has (I believe) a currency control marking in magenta. This itself is a spectacular usage, an uncommon to rare Canal Zone to Dutch East Indies usage. In addition, since the 10c franking was more than the 3c surface rate to the US and the 5c air rate to the US, but less than the 30c air rate to Asia, the cover is marked "BY AIR TO AND IN USA" since the 10c covered that 5c domestic air rate but only 5c more - I believe the 5c surface rate from the US to Asia. Return address to a US-based FDC servicer in Baltimore. F/VF and clean and bright without faults, a great addition to a Canal Zone postal history collection.