1. Lecture 12:Approach Lighting System

2. Introduction
Approach Lighting System (ALS) is the tail end of the Air Navigation System.
It is a lighting systems installed on the Approach end of an Airport.
ALS consist of a series of Light bars and Strobe lights

3. ALS uses
ALS serve the runway that has the Instrument Approach Procedure such as Instrument Landing System (ILS).
ALS allows the pilot to see and identify the Runway end and align the aircraft to land on the runway.
At the point where Decision Height is reached, pilot must be able to see ALS, then pilot can continue the approach.
While approach, pilot will follow the ILS and descend along the glideslope, until the Decision height based on ILS categories is reached.
At this point, the pilot must have the runway or its approach lights in sight to continue the approach.

4. ALS uses
If pilot can not see the ALS, the approach must be aborted and a missed approach procedure will be performed.
This is where the aircraft will climb back to a predetermined altitude and position.
From there the pilot will either try the same approach again, try a different approach or divert to another airport.

5. ALS Configurations
ALS are designed to allow the pilot to quickly and positively identify visibility distances under Instrument Flight Rules (IFR).
The most common approach light system configurations include:
ALSF-1: Approach Lighting System with Sequenced Flashing Lights configuration 1
ALSF-A2: Approach Lighting System with Sequenced Flashing Lights configuration 2
The most common approach light system configurations include:
ALSF-1: Approach Lighting System with Sequenced Flashing Lights configuration 1
ALSF-2: Approach Lighting System with Sequenced Flashing Lights configuration 2

6. Approach Lighting System Configuration 2
Used on Category II runways during instrument landing approach to align the aircraft with the centerline of the runway and to establish vertical orientation.
Up to 174 steady burning white lights serve as a reference plane,
Two rows of red side row increase the pilots horizontal perception.
Up to twenty-one white lights create a sequential strobing flash pattern that rolls toward the runway threshold.
Three intensity settings allow the approach to be used under changing weather conditions.
Approach lighting systems provide landing approach guidance for pilots. Several different configurations are available:
ALSF I (Approach Lighting System with Sequenced Flashing Lights) is used on Category I runways during instrument landing approach to align the aircraft with the centerline of the runway and to establish vertical orientation. Up to twenty-one white lights create a sequential strobing flash pattern that rolls toward the runway threshold.
The Dual Mode ALSF II/SSALR approach lighting system allows Category II runways to operate in either the full ALSF II mode or in the economical SSALR mode, depending on weather conditions.
ALSF II (Approach Lighting System with Sequenced Flashing Lights) mode is used on Category II runways during instrument landing approach to align the aircraft with the centerline of the runway and to establish vertical orientation. Up to 174 steady burning white lights serve as a reference plane, and two rows of red side row barrettes increase the pilots horizontal perception. Up to twenty-one white lights create a sequential strobing flash pattern that rolls toward the runway threshold. Three intensity settings allow the approach to be used under changing weather conditions.
SSALR (Simplified Short Approach Lighting System with Runway Alignment Indicator Lights) mode is used during instrument landing approach to align the aircraft with the centerline of the runway. The white steady burning lights of the ALSF II are greatly reduced to conserve power under improved visibility and the side row barrettes are not powered. Up to sixty-three steady-burning lights are used to create a reference plane, and up to eight lights create a sequential strobing flash pattern that rolls toward the runway threshold. SSAL (Simplified Short Approach Lighting System) is available.
A 6.6a series circuit powers each approach system. This provides for greater dependability, increased control, decreased maintenance, improved efficiency and lower installation costs.

7. Approach Lighting configuration 2

10. Importance of Approach Lighting System
As Approach Lighting System (ALS) is the tail end of the Air Navigation System, it is important to affect the aircraft landing.
ALS allows the pilot to see and identify the Runway end and align the aircraft to land on the runway.
It very important especially during night time, bad weather and poor visibility
ALS also important to verify positive contact and let you know where the begin an end of the runway is.

11. Visual Approach Slope Indicators (VASI)
Function: To assist pilot with visual guidance during an aircraft landing
by indicate the pilot’s right angle of approach.

12. Visual approach slope indicator
VASI are light systems to let you know your position in relation to the desired glide path in landing to the runway.
They are located on the side of the runway and can be used both during the day and at night.

14. Visual Approach Slope Indicators (VASI)
VASI may have 2 bars (rows) of lights.
A 2-bar system has one near and one far bar. Each bar can contain 2 light units.
If both bars show white lights, you are too high for your landing.
If both bars show red, you are too low.
If the far bar is red and the near bar is white you are just right (be on the glide path).

15. Visual Approach Slope Indicators (VASI)
Visible from 3-5 miles during the day and up to 20 miles or more at night.

16. Visual Approach Slope Indicators (VASI)

17. Precision Approach Path Indicator (PAPI)
PAPI work in a similar manner to the VASI.
The difference is PAPI only have one row of lights.
This one row contain 4 light units.
If all four lights show white, you are too high for your landing.
If all four lights show red, you are too low.
If two lights show red and two lights show white you are just right (be on the glide path).

18. Precision Approach Path Indicator (PAPI)