Posted this in the pre-decimal commercial covers thread, but Brad suggested putting it here. Completely agree
1947 (Feb 3) solo usage of the 1942 5½d Emu paying the combined registration and letter rate within the British Empire; from Melbourne to British philatelist Francis John Field in Sutton Coldfield, England.
This cover was sent from the fifth and last Regional Air Navigation (RAN) Meeting of the Provisional International Civil Aviation Organization (PICAO) for the South Pacific Region, which was held Feb 4-22, 1947, on the premises of the Union Building of the University of Melbourne, Victoria, Australia.
This cover was cancelled on Feb 3, 1947, the day before the meeting officially opened, when a special post office was opened at the University for the event. It features the conference's hand-stamped, blue, provisional C6 registration label, showing the boxed PICAO initials and location, "Melb. - Aust.", below.
Detail of the PICAO blue provisional C6 registration label.
The information above was taken from the excellent website on the postal history of the International Civil Aviation Organization (ICAO)...
Index:
https://www.icao.int/secretariat/PostalHistory/index.html
Melbourne 1947:
https://www.icao.int/secretariat/PostalHistory/1947_melbourn ... eeting.htm
The International Civil Aviation Organization (ICAO) website for the Melbourne 1947 conference (see link above), features an almost identical example of this cover to Francis J. Field, registration No. 41. My example is No. 36, and was clearly prepared at the same time.
Sister cover to my own featured on the ICAO website.