The Civil Air Ensign is the flag

Civil air ensign

A nation's civil air ensign is its national flag which represents civil aviation in that nation. Typically, it is flown from buildings connected with the administration of civil aviation and it may also be flown by airlines of the appropriate country. A civil air ensign is the equivalent of the...

 that may be flown at airports in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 and from landed British aircraft.

The ensign's field is light blue and has a dark blue Latin cross which is fimbriated white placed overall. The Union Flag

Union Flag

The Union Flag, also known as the Union Jack, is the flag of the United Kingdom. It retains an official or semi-official status in some Commonwealth Realms; for example, it is known as the Royal Union Flag in Canada. It is also used as an official flag in some of the smaller British overseas...

 is in the canton.

The Civil Air Ensign was instituted by an Order in Council on 11 August 1931. The order stated that "An ensign called the Civil Air Ensign is the proper national colour to be flown by aircraft and air transport undertakings and at aerodromes." It was first hoisted by The Hon Mrs Victor Bruce, the noted British aviatrix.

It was part of the livery, as the tail logo, of the Civil Aviation Flying Unit (CAFU)

The Civil Air Ensign is also the basis for the Australian Civil Air Ensign

Australian Civil Aviation Ensign

The Australian Civil Aviation Ensign is an Australian flag that was used by the Australian Civil Aviation Authority.The design of the flag is based on the British Civil Air Ensign, which is divided into quarters by a dark blue cross with a white fimbriation. There is a Union Jack in the upper hoist...

, the New Zealand Civil Air Ensign

New Zealand Civil Air Ensign

The New Zealand Civil Air Ensign is the flag that represents civil aviation in New Zealand.The ensign consists of a dark blue Latin cross edged with white on a light blue field. A Union Jack is placed in the first quarter and the Southern Cross, as seen from New Zealand, are shown in red in the...

 and other Commonwealth

Commonwealth of Nations

The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

countries: