- -The wires, cables to be marked should be equipped with markers;the supporting towers should be colored.
Marking by colors
- -The supporting towers of overhead wires, cables that require marking should be marked in accordance with 1.1 and 1.2(see below)except that the marking of the supporting towers may be omitted when they are lighted by high intensity obstacle lights by day.
(1.1 All fixed objects to be marked shall,whenever practicable, be colored, but if this is not practicable, markers or flags shall be displayed on or above them, except that objects that are sufficiently conspicuous by their shape, size or color need not be otherwise marked.
1.2 All objects shall be colored in a single conspicuous color if its projections on any vertical plane has both dimension less than 1.5m. Orange or red should be used, except where such colors merge with the background.)
Marking by markers
- -Markers displayed on or adjacent to objects shall be located in conspicuous locations so as to retain the general definition of the object and shall be recognizable in clear weather from a distance of at least 1000m for an object to be viewed from the air and 300m for an object to be viewed from the ground in all directions in which an aircraft is likely to approach the object. The shape of markers shall be distinctive to the extinct necessary to ensure that they are not mistaken for markers employed to convey other information, and they shall be such that the hazard presented by the object they mark is not increased.
- -A marker displayed on the overhead wires, cables should be spherical and have a diameter of no less than 60cm.
- -The spacing between two consecutive markers or between a marker and a supporting tower should be appropriate to the diameter of the marker, but in no case should the spacing exceed:
(a)30m where the marker diameter is 60cm progressively increasing with the diameter of the marker to
(b)35m where the marker diameter is 80cm and further progressively increasing to a maximum of
(c)40m where the marker diameter is of at least 130cm.
Where multiple wires and cables are involved, a marker should be located not lower than the level of the highest wire at the point marked.
- -The marker should be of one color. When installed,white and red, or white and orange markers should be displayed alternately. The color selected should contrast with the background against which it will be seen.
- -When it has been determined that an overhead wire and cable needs to be marked but it is not practicable to install markers on the wire and cable, then high-intensity obstacle lights, Type B, should be provided on their supporting towers.
- -High-intensity obstacle lights, Type B should be used to indicate the presence of a tower supporting of overhead wires and cables , where:
- an aeronautical study indicates such light to be essential for the recognition of the presence of wires and cables etc. or
- It has not been found practicable to install markers on the wires and cables,etc.
- when high-intensity obstacle lights,Type B are used, they shall be located at three levels;
—at the top of the tower;
—at the lowest level of the catenary of the wires or cables;
—at approximately midway between these two levels.
Note. —In some cases, this may require locating the lights off the tower.
- -High-intensity obstacle lights, Type B , indicating the presence of a tower supporting overhead wires, cables, etc.,should flash sequentially; first the middle light; second the top light and last;the bottom light. The intervals between flashes of the lights should approximate the following ratios:
Flash Intervals Between Ratio of Circle Time
Middle and top light 1/13
Top and bottom light 2/13
Bottom and middle light 10/13
Note. —High-intensity obstacle lights are intended for day use as well as night use.Care is needed to ensure that these lights do not create disconcerting dazzle. Guidance on the design, operation and location of the high-intensity obstacle lights is given in the Aerodrome Design Manual(Doc 9157,Part 4).
- -Where, in the opinion of the appropriate authority, the use of high-intensity obstacle lights, Type B, at night may dazzle pilots in the vicinity of an aerodrome (within approximately 10000m radius) or cause significant environment concerns, a dual obstacle lighting system should be provided.This system should be composed of high-intensity obstacle lights,Type B, for daytime and twilight use and medium-intensity obstacle lights, Type B, for night use. Where medium-intensity lights are used they should be installed at the same level as the high-intensity obstacle light Type B.
- -The installation setting angels for high-intensity obstacle lights, Type B, should be in accordance with table 6-5.
Table 6-5. Installation setting angels for high-intensity obstacle lights
Height of light unit above terrain
Angel of the peak of the beam above horizontal