(1) Maximum visibility of obstructions by contrast in colors can best be obtained by the use of aviation surface orange and white. Paints and enamels of these colors have been developed for use by government agencies and private industry in marking obstructions to air navigation. In marking, either the aviation surface orange paint or enamel may be used as preferred.

(2) The painted surfaces of obstructions should be cleaned or repainted as often as necessary to maintain good visibility.

(3) If the smooth surface of the paint on the ladders, decks, and walkways of certain types of steel towers and similar structures presents a potential danger to maintenance personnel, such surfaces need not be painted. However, the omission of paint should be restricted to actual surfaces the painting of which will present a hazard to maintenance personnel, and care should be taken that the over-all marking effect of the painting is not reduced.

(4) Solid. Obstructions the projection of which on any vertical plane has both dimensions less than 5 feet should be colored aviation surface orange.

(5) Bands.

(a) Towers, poles, smokestacks and similar obstructions, as well as buildings of certain shape and dimensions, having essentially unbroken surfaces the projection of which on any vertical plane is 5 feet or more in one dimension and is less than 15 feet in the other dimension, and any skeleton or smokestack type obstruction having both dimensions 5 feet or more, should be colored to show alternate bands of aviation surface orange and white.

(b) The bands should be perpendicular to the major axis of the obstruction with the band at each end colored aviation surface orange. The widths of the bands should be equal and the width of each band should be approximately one-seventh of the length of the major axis of the obstruction, provided that each band shall have a width of not more than 40 feet nor less 1 1/2 feet. If it is technically impracticable to color the roof of a building to show alternate bands of aviation surface orange and white, such roof may be colored aviation surface orange.

(6) Checkerboard pattern.

(a) Water towers, grain elevators, gas holders, and similar obstructions, as well as buildings of certain shape and dimensions, having essentially unbroken surfaces the projection of which on any vertical plane is 15 feet or more in both dimensions, should have their top and vertical surfaces colored to show a checkerboard pattern of alternate rectangles of aviation surface orange and white. If it is technically impracticable to color the roof of a building to show alternate rectangles of aviation surface orange and white, such roof may be colored aviation surface orange.

(b) The sides of the rectangles should measure not less than 5 feet nor more than 20 feet. The rectangles at the corners of surfaces should be colored aviation surface orange.

(c) If a part of a water tower, gas holder, building, or similar obstruction consists of a skeleton type construction, that portion of the obstruction should be colored with alternate bands of aviation surface orange and white as specified for towers, poles, smokestacks and similar obstructions. In this case, if the portion of the obstruction, which is to be colored to show a checkerboard pattern of alternate rectangles of aviation surface orange and white, has any surfaces the projection of which on any vertical plane is less than 15 feet in either dimension, the alternate rectangles of aviation surface orange and white may have dimensions of less than 5 feet on a side, provided their dimensions remain as close as is practicable to the minimum 5 feet specified for coloring by the checkerboard pattern.

(7) If the size and shape of water towers, grain elevators, gas holders and similar obstructions come within the dimensions set forth under the specification for coloring by bands; or if their type of construction does not permit coloring by the checkerboard pattern as hereinbefore described, then such obstructions should be colored by bands as specified for towers, poles, smokestacks and similar obstructions. Where this method of coloring is employed, the top aviation surface orange band should be continued from the vertical surface so as to cover the entire top of the obstruction.

(8) If a part, or all, of certain obstructions such as water towers and gas holders of spherical shape does not permit the exact application of the checkerboard pattern of coloring, then the shape of the alternate rectangles of aviation surface orange and white covering the spherical shape may be modified to fit the particular shape of the structural surface, provided the dimensions of these modified rectangles remain to the extent practicable within the dimensional limits set forth in the specifications for coloring by the checkerboard pattern.

(9) If certain obstructions such as gas holders and grain elevators are of such large size that the application of the checkerboard pattern of coloring to the complete outer surface of the structure would be impracticable, the application of the checkerboard pattern of coloring may be limited to the upper one-third of the structure, provided aeronautical study indicates that the modified marking will provide adequate protection for air navigation.