The British Civil Air Ensign is the flag that may be flown at civil aviation establishments in the United Kingdom and be displayed on UK-registered civil aircraft.
The ensign's field is light blue and has a dark blue Latin cross which is fimbriated white placed overall. The Union Flag 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." The first Civil Air Ensign to be flown in London was hoisted by The Hon Mrs Victor Bruce, the noted British woman aviator.