Approach Lighting System Explained!

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:

1. Simple Approach Lighting System – recommended for Non-instrument runway and Non-precision approach runway
2. 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)
3. 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:

1. row of lights on extended runway center line possibly over a distance not less than 420 metre from threshold
   and
2. row of light forming the crossbar 18 m or 30 m in length at distance of 300 m from threshold

associated requirements: lights forming center line are placed at interval of 30 m or 60 m lights forming crossbar are placed at interval 1 m to 3 m additional crossbar at 150 m from threshold can also be placed if 420 m length is not possible, row of lights can be extended to 300 m so as to include crossbar if 300 m length is also not possible each center line light should then consist of a barrette at least 3 m in length

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:

1. row of lights on extended runway center line possibly over a distance of 900 metre from threshold
   and
2. 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: lights forming center line are placed at interval of 30 m lights forming crossbar are placed at interval 1 m to 4 m

Light of Precision Approach Category 1 lighting system shall be fixed lights showing variable white. Each centre line light position shall consist of: a single light source in innermost 300 m of centre line, two light sources in central 300 m of centre line and three light source in the outer 300 m of centre line to provide distance information (additional crossbars of lights are also required at 150m, 450m, 600m and 750m from threshold) OR a barrette with supplemented flashing light and length of at least 4 m.

---

PRECISION APPROACH CATEGORY 2 and 3 LIGHTING SYSTEM

Precision Approach Category 2 and 3 lighting system consist of:

1. row of lights on extended runway center line possibly over a distance of 900 metre from threshold
   and
2. two side rows of lights extending 270 m from runway threshold
   and
3. 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: lights forming center line are placed at interval of 30 m lights forming side rows shall be placed on each side of centre line at interval of 30 m side rows should have barrettes showing red lights (at least 4 m in length)

Light of Precision Approach Category 2 and 3 lighting system shall be: center line for first 300 m from threshold shall consist of barrettes showing variable white (exception of signal light sources for 300 m displaced threshold) beyond 300 m from threshold each center line light position shall consist of a barrette as used in inner 300 m OR two light sources in central 300 m of centre line and three light sources in outer 300 m of centre line (all should show variable white)

---

---

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