A

Approach

L

Light

S

System

Approach Light Systems help you to identify the runway environment during night and

especially during low visibility weather condition. Therefore, they can help you to transition from IMC or Instrument to visual flight just before touchdown.

ALS-Systems.png

As you can see in the picture above there are 13 different ALS configurations available, 11 of which are being used in the U.S.  The 'Calvert & Calvert-2' are only used at in the UK.

The Approach Light Systems are divided into the following 2 categories:

 

Precision Runways:

 

ALSF1
Approach Light System with Sequenced Flashing Lights

ALSF2
Approach Light System with Sequenced Flashing Lights

(different looks as ALSF1; extends 2.400 – 3.400ft from RWY threshold;

consists of High Steady burning white lights & sequenced flashing white lights;

has 5 red bars next and parallel to the threshold)

 

MALSR
Medium Intensity Approach Light System with Runway alignment indicator lights

 

CALVERT(1+2)
According to ICAO → HIALS = High Intensity Approach Light System

 

SSALR
Simplified Short Approach Light System with Runway alignment indicator lights

(extends 2.400 – 3.400ft from the RWY threshold; has High & Steady burning white light bars)

 

Non – Precision Runways:

MALSF
Medium Intensity Approach Light System with Sequenced Flashing Lights

 

SSALF
Simplified Short Approach Light System with Sequenced Flashing Lights

(extends 1.400 – 1.500 ft out from the RWY threshold – comparable to MALSR/SSALR)

 

ODALS
Omnidirectional Approach Light System

(extends 1.500ft out from the RWY threshold)

 

RAIL
Runway Alignment Indicator Lights

(extends ~ 1000ft from the RWY threshold; has sequenced flashing lights)

 

REIL
Runway End Identifier Lights

 

ODALS
Omnidirectional Approach Light System

(extends 1.500ft from the threshold)

 
 

Visual Descent Indicators

VASI
(Visual Approach Slope Indicators)

- provides 10 obstacle clearance to the left/right of the RWY centerline
out to 4nm from the RWY threshold

- it's visible from 5nm during the day and 20nm at night

 

The VASI exists in the following configurations:

2BarVasi.png

2 – Unit Bars located at 500 – 1000ft from the threshold

3BarVasi.png

3 – Unit Bars developed for high Cockpit aircraft

2+3BarVasi.png
 

PAPI

(Precision Approach Path Indicator)

 

- visible from 5nm during the day and 20nm at night

- located on the right side of the RWY

PAPI.png
 

PVASI

(Pulsating VASI)

- consists of a single light unit with 2 colors

usable/visible range:

4 miles during the day / up to 10 miles at night

PVASI.png
 

T-VASI

(T-shaped glide path Indicator)
originated in Australia

TVasi.JPG
 

Tri - Color VASI

As the name implies, this VASI (single light unit) indicates you your position relative to the correct glide path with three different light colors as follows:

Below GP

ON GP

Above GP

usable/visible range:

 

during the day = ½ to 1 mile

during the night = 5 miles