Airmail stamp
An airmail stamp is a postage stamp intended to pay either an airmail fee that is charged in addition to the surface rate, or the full airmail rate, for a piece of mail to be transported by air.
Airmail stamps should not be confused with airmail etiquettes, which are affixed to mail as an instruction to the postal authority that the mail should be transmitted by air.
Development
History
With aviation developments, several countries started to experiment with flights, and postal authorities considered flying the mails. Initially flights were unofficial, but some flights such as the 1877 Buffalo balloon flight, carried mail, to which stamp-like labels were affixed. At the beginning airmail letters cost more than surface mail.
Both airmail stamps and stamps surcharged for airmail were issued, though some countries restricted the use of airmail stamps only to letters sent by airmail, while others allowed them to be used for other mail services.
The 20-cent U.S. Parcel Post issue of 1912 was the first stamp in the world to show an airplane, and its caption specifically labeled it as an example of how mail could be carried, but it was not issued for that express purpose. It was several years before an actual airmail stamp was issued. Several of the early ones were produced by surcharging other stamps with overprints; at first in 1917, Italy used express stamps; regular stamps were used by Austria in 1918, Sweden used official stamps in 1920. Some other examples are the use of fiscal stamps, telegraph stamps, postage due stamps, and parcel stamps by other countries. Airmail stamps have been issued for extra services, such as registered airmail, express airmail, airmail fieldpost, and even with welfare surcharges.