(1) Flags may be used to mark obstructions when it has been determined that marking such obstructions by coloring or by markers is technically impracticable.

(2) The flags should be displayed around or on top of the obstruction or around its highest edge and should not increase the hazard presented by the obstruction they mark. When flags are used to mark extensive obstructions or groups of closely spaced obstructions, they should be displayed at approximately 50 foot intervals.

(3) The flags should be rectangular in shape and have stiffeners to keep them from drooping in calm or light wind. The flag stakes should be of such strength and height that they will support the flags free of the ground, vegetation, or nearby surfaces.

(4) The flags should be in accordance with one of the following patterns:

(a) Solid color aviation surface orange not less than two feet on a side.

(b) Two triangular sections, one of aviation surface orange and the other of aviation surface white, combined to form a rectangle not less than two feet on a side.

(c) A checkerboard pattern of aviation surface orange and aviation surface white squares, each one foot plus or minus 10 percent on a side, combined to form a rectangle not less than three feet on a side.