In 1996, the United Nations General Assembly proclaimed that 7 December was to be the International Civil Aviation Day.
The day has been celebrated by the International Civil Aviation Organization (ICAO) since 7 December 1994, the 50th anniversary of the signing the Convention on International Civil Aviation. The purpose of the day is to recognize the importance of aviation, especially international air travel, to the social and economic development of the world.
Official page of International Civil Aviation Day on ICAO website
The Postal History of ICAO : International Civil Aviation Day
UN: International Civil Aviation Day