are spaced 10 feet apart. Their color is aviation green. (See fig. 6-35.)

Winged-Out Threshold Lights. - The winged- out threshold light bar is on the same light line as the inboard lights. These lights extend out from the end of each side of the inboard light bar. Each bar is 40 feet long and has nine lights spaced 5 feet apart. The first light location is at the intersection of the runway edge light line and the threshold light line. The color of these lights is also aviation green. (See fig. 6-35.)

Prethreshold Wing Bars. - A prethreshold wing bar is located on each side of the extended runway center line 100 feet out from the threshold. The innermost light of the bar is 75 feet from the center line. Each bar (14 feet long) has five aviation red lights spaced 3 l/2 feet apart. (See fig. 6-35.)

Terminating Bar. - The terminating bar is located in the overrun area. The light bar is at a right angle to the runway center line and 200 feet out from the runway threshold (100 feet out from the prethreshold lights). There are 11 aviation red lights in the bar. The bar is 50 feet long and is arranged so that one half of the bar is on each side of the center line. The lights are arranged in three groups: five lights spaced 3 l/2 feet apart on a 14-foot bar in the middle and, on each side, one I O-foot bar of three lights spaced 5 feet apart. (See fig. 6-35.)

Obstruction Lights Obstruction lighting is a system of red lights used to show the height and width of natural or man-made objects that are hazardous to air flight. These lights are for the safety of aircraft in flight. The lights must be seen from all directions and are aviation red in color.

The obstruction lights are turned on during all hours of darkness and during periods of restricted visibility. They are placed on all objects with an overall height of more than 150 feet above ground or water within the airspace.

At least two lights (or one light fixture with two lamps) are located at the top of the obstruction. When the top of an obstruction is more than 150 feet above the level of the surrounding ground, an intermediate light. or lights, is provided for each 150 feet. These lights are equally spaced from the top to the bottom.

Where obstructions cover an extensive horizontal plane, the top lights will be put on the point or edge of the obstruction highest in relation to the obstruction- marking surface. The lights should not be spaced more than 150 feet apart. This spacing indicates the general extent of the obstruction. Double lights are used at the horizontal limits of the obstruction, and single lights are used for intermediate lights. If two or more edges are of the same height. the edge nearest the airfield is lit.

On overhead wires, obstruction lights are placed at intervals not exceeding 150 feet and at a level not below that of the highest wire at each light location.

Obstruction lighting systems are served by, either a series or a multiple circuit. The type of circuit used depends on the location of the obstruction and the type of lighting equipment installed. The six most common types of circuits that may be used for the obstruction lights are as follows:

1. Low-voltage multiple service from the vault when the length of the circuit is less than 800 feet

2. Series circuit when the load is less than 4 kilowatts (kW) from a taxiway type of regulator in the vault

3. Twenty-four hundred-volt service from the vault to a distribution transformer to serve a multiple circuit

4. Twenty-four hundred-volt service from the vault to a CCR that serves a series circuit

5. Control circuit from the vault that operates any of the previously listed circuits by means of a relay

6. Time clock or a photocell with a series or multiple circuit for the lights

Obstruction lights on objects that are more than 150 feet above ground or water must be on all the time or controlled by a photocell.

Beacon Lights

The landing facility location is provided by the aeronautical beacon. The beacon is a high candlepower flashing light visible throughout 360 degrees. It provides the pilot a visual signal to locate and identify airfields during night operations or during periods of restricted visibility, day or night.

There are three functional types of beacons that we will discuss: the airport beacon; the identification, or code beacon; and the hazard, or obstruction beacon.

The airport beacon is normally located within 5,000 feet of the airfield. The rotatable unit will display