Lecture 11:Approach Lighting

System (ALS)

Learning Outcomes

At the end of this lecture, the student should be able to: Describe the theory and use of Approach

Lightings System (ALS) and their importance during aircraft landing.

Why Approach Lighting Systems is important?

Importance of Lighting

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Lighting systems from the cockpit window during bad weather. Poor visibility is mainly due to

heavy snowfall

Lighting systems are important for a/c landing during night time.

Importance of Approach Lighting System

Approach Lighting System (ALS) is the tail end of the Air Navigation System, thus, 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.

What pilot should do if he unable to see the ALS?

ALS uses

At the point where Decision Height is reached, pilot must be able to see ALS, then pilot can continue the approach.

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.

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-2: Approach Lighting System with

Sequenced Flashing Lights configuration 2

Approach Lighting System Configuration 2

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 flash pattern that rolls toward the runway threshold.

Approach Lighting Systems (ALS)

1. Sequence Flashing LightTo guide the pilot’s eyes

toward the runway centerline

Thresholds Light: Appear green for a/c landing

and red a/c take-off

3. Approach Light•Warning red light, which a/c

should not land yet

2. Cross Bar Light

•Indicate a/c wings status

Runway Touch Down Zone Light

•Give depth view of the runway

Approach Lighting

System (ALS)

Visual Approach Slope Indicators (VASI)

VASI

VASI are light systems to assist pilot with visual guidance during an aircraft landing by indicate the pilot’s right angle of approach.

They are located on the side of the runway and can be used both during the day and at night.

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).

Visual Approach Slope Indicators (VASI)

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Visual Approach Slope Indicators (VASI)

Precision Approach Path Indicator (PAPI)

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).

Precision Approach Path Indicator (PAPI)

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