12.2.3 Tri.color Systems. Tri.color visual ap-proach slope indicators normally consist of a single light unit, projecting a three.color visual approach path into the final approach area of the runway upon which the indicator is installed. The below glide path indication is red, the above glide path indication is amber, and the on glide path indication is green. These types of indicators have a useful range of approximately 1/2 to 1 mile during the day and up to 5 miles at night depending upon the visibility conditions. (See FIG AD 1.1.6.)
12.2.4 Pulsating Systems. Pulsating visual ap-proach slope indicators normally consist of a single light unit projecting a two.color visual approach path into the final approach area of the runway upon which the indicator is installed. The on glide path indication is a steady white light. The slightly below glide path indication is a steady red light. If the aircraft descends further below the glide path, the red light starts to pulsate. The above glide path indication is a pulsating white light. The pulsating rate increases as the aircraft gets further above or below the desired glide slope. The useful range of the system is about four miles during the day and up to ten miles at night. (See FIG AD 1.1.7.)
12.2.5 Alignment of Elements Systems. Align-ment of elements systems are installed on some small general aviation airports and are a low cost system consisting of painted plywood panels, normally black and white or fluorescent orange. Some of these systems are lighted for night use. The useful range of these systems is approximately 3/4 mile. To use the system the pilot positions the aircraft so the elements are in alignment. The glide path indications are shown in FIG AD 1.1.8.
12.3 Runway End Identifier Lights (REIL)
12.3.1 REILs are installed at many airfields to provide rapid and positive identification of the approach end of a particular runway. The system consists of a pair of synchronized flashing lights, one of which is located laterally on each side of the runway threshold facing the approach area. They are effective for:
12.3.1.1 Identification of a runway surrounded by a preponderance of other lighting.
12.3.1.2 Identification of a runway which lacks contrast with surrounding terrain.
12.3.1.3 Identification of a runway during reduced visibility.
12.4 Runway Edge Light Systems
12.4.1 Runway edge lights are used to outline the edges of runways during periods of darkness or restricted visibility conditions. These light systems are classified according to the intensity or brightness they are capable of producing: they are the High Intensity Runway Lights (HIRL), Medium Intensity Runway Lights (MIRL), and the Low Intensity Runway Lights (LIRL). The HIRL and MIRL systems have variable intensity controls; whereas, the LIRLs normally have one intensity setting.
12.4.2 The runway edge lights are white; except on instrument runways, yellow replaces white on the last 2,000 feet or half the runway length, whichever is less, to form a caution zone for landings.
12.4.3 The lights marking the ends of the runway emit red light toward the runway to indicate the end of the runway to a departing aircraft and emit green outward from the runway end to indicate the threshold to landing aircraft.
12.5 In.Runway Lighting
12.5.1 Runway Centerline Lighting System (RCLS). Runway centerline lights are installed on some precision approach runways to facilitate landing under adverse visibility conditions. They are located along the runway centerline and are spaced at 50.foot intervals. When viewed from the landing threshold, the runway centerline lights are white until the last 3,000 feet of the runway. The white lights begin to alternate with red for the next 2,000 feet, and for the last 1,000 feet of the runway, all centerline lights are red.
12.5.2 Touchdown Zone Lights (TDZL). Touch-down zone lights are installed on some precision approach runways to indicate the touchdown zone when landing under adverse visibility conditions. They consist of two rows of transverse light bars disposed symmetrically about the runway centerline. The system consists of steady.burning white lights which start 100 feet beyond the landing threshold and extend to 3,000 feet beyond the landing threshold or to the midpoint of the runway, whichever is less.

Federal Aviation Administration Twentieth Edition
FIG AD 1.1.1
Precision & Nonprecision Configurations

NOTE.

Civil ALSF.2 may be operated as SSALR during favorable weather conditions.
FIG AD 1.1.2
2-Bar VASI
Far Bar

= Red
Near Bar

= White

Below Glide Path On Glide Path Above Glide Path
FIG AD 1.1.3
3-Bar VASI

FIG AD 1.1.4
VASI Variations

2 Bar  2 Bar  3 Bar 
2 Light Units  12 Light Units  16 Light Units 
On Glide Path  On Glide Path  on Lower Glide Path 
　
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