The Air Navigation Order 1989

I.  Position of Marks

(a) Flying Machines and Gliders

(i) Horizontal Surfaces of the Wings or Fuselage (or equivalent structure).

(aa) On aircraft having a fixed wing surface, the marks shall appear on the lower surface of the wing structure, and shall be on the left half of the lower surface of the wing structure unless they extend across the whole surface of both wings. So far as possible the marks shall be located equidistant from the leading and trailing edges of the wings. The tops of the letters shall be towards the leading edge of the wing.

(bb) On aircraft having no fixed wing surface and when owing to the structure of the aircraft the greatest height reasonably practicable for the marks on the vertical surface of the fuselage (or equivalent structure) is less than 15 centimetres the marks shall also appear on the lower surface of the fuselage on the line of symmetry and shall be placed with the tops of the letters towards the nose.

(ii) Vertical Surfaces of the Tail or Fuselage (or equivalent structure).

The marks shall also be on each side of the aircraft either on the fuselage or on the upper halves of the vertical tail surfaces. On aircraft having a fixed wing surface, the marks, if placed on the fuselage (or equivalent structure), shall be between the horizontal tail surfaces and the wing. When on a single vertical tail surface, the marks shall be on both sides. When there is more than one vertical tail surface, the marks shall be on the outer sides of the outboard vertical tail surfaces.

(b) Airships and Free Balloons

(i) Airships: The marks shall be on each side of the airship. They shall be placed horizontally either on the hull near the maximum cross-section of the airship or on the lower vertical stabiliser.

(ii) Free Balloons: The marks shall be in two places diametrically opposite.

(iii) In the case of all airships and free balloons the side marks shall be so placed as to be visible both from the sides and from the ground.