8/15/19 AIM  wire span. The lights are beamed towards the companion structure and identify the area of the wire span. d. High intensity flashing white lights are also employed to identify tall structures, such as chimneys and towers, as obstructions to air navigation. The lights provide a 360 degree coverage about the structure at 40 flashes per minute and consist of from one to seven levels of lights depending upon the height of the structure. Where more than one level is used the vertical banks flash simultaneously. Air Navigation and Obstruction Lighting 2 − 2 − 2