Approach light system(ALS) is part of aviation ground lighting patters primarily used for identification and aircraft alignment with runway center line. ALS is made of several parts collectively working to serve the said purpose. Availability of ALS category for runway depends on its licensing category and need for continuous operation during period of poor visibility.
Approach light system has been categorized by ICAO into three major categories and installation is depending on runway type:
- Simple Approach Lighting System – recommended for Non-instrument runway and Non-precision approach runway
- Precision Approach Category 1 Lighting System – recommended for Precision approach category 1 runway (ALS less than 900 m in length OR no installation at all may result in operational limitations on use of runway)
- Precision Approach Category 2 and 3 Lighting System – mandatory for Precision approach category 2 runway and Precision approach category 3 runway
There is no fix/specific designed type dedicated to each category. Some flexibility has been provided to mach up with difference runway demographic requirements. More details follow in this article. Data has been summarized from ICAO Annex 14 Volume 1.
Also check : Runway Reference Code Numbers and Code Letters
SIMPLE APPROACH LIGHTING SYSTEM (SALS)
Simple ALS consist of:
- row of lights on extended runway center line possibly over a distance not less than 420 metre from threshold
and - row of light forming the crossbar 18 m or 30 m in length at distance of 300 m from threshold
associated requirements:
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Light of SALS shall be fixed light and color of lights shall be such that it can be distinguished from other aeronautical ground lights. Each centre line light shall consist of either single source or a barrette at least 3 m in length. |
Additional Notes:
- at location where identification of ALS is difficult due to surrounding lights, sequence flashing lights can be installed in outer portion of system
- when ALS is provided for non instrument runway, lights should show at all angles in azimuth necessary to pilot on base leg and final approach
- when provided for non-precision approach runway, lights should show at all angles in azimuth necessary to pilot on final approach
PRECISION APPROACH CATEGORY 1 LIGHTING SYSTEM
Precision Approach Category 1 lighting system consist of:
- row of lights on extended runway center line possibly over a distance of 900 metre from threshold
and - row of light forming the crossbar 30 m in length at distance of 300 m from threshold
ALS less than 900 m in length may result in operational limitations on use of runway
associated requirements:
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Light of Precision Approach Category 1 lighting system shall be fixed lights showing variable white.
Each centre line light position shall consist of:
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PRECISION APPROACH CATEGORY 2 and 3 LIGHTING SYSTEM
Precision Approach Category 2 and 3 lighting system consist of:
- row of lights on extended runway center line possibly over a distance of 900 metre from threshold
and - two side rows of lights extending 270 m from runway threshold
and - row of light forming the crossbar at distance of 150 m and 300 m from threshold (2 crossbars)
Length of 900 m is based on providing operations under category 1, 2 and 3 conditions. Reduced length may support category 2 and 3 operations but may impose limitations on category 1 operations.
associated requirements:
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Light of Precision Approach Category 2 and 3 lighting system shall be:
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FALS (Full – ALS) |
IALS (Intermediate – ALS) |
BALS (Basic – ALS) |
NALS (No – ALS) |
Precision approach CAT 1 lighting system (HIALS 720m and more), distance coded centreline, barrette centreline | Simple approach lighting system (HIALS 420 – 719m) single source barette | Any other approach lighting system (HIALS, MIALS or ALS 210- 419m) | Any other aporach lighting system (HIALS, MIALS, or ALS less than 210m) or no approach lights |
HIALS – high intensity approach lighting system
MIALS – medium intensity approach lighting system