A
L
S
Approach
Light
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.
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:
2 – Unit Bars located at 500 – 1000ft from the threshold
3 – Unit Bars developed for high Cockpit aircraft
PAPI
(Precision Approach Path Indicator)
- visible from 5nm during the day and 20nm at night
- located on the right side of the RWY
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
T-VASI
(T-shaped glide path Indicator)
originated in Australia
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