Low Visibility Operations Masterclass | Part 4

A Deep Dive into Key Design Features and Techniques

Hey everyone and welcome back to this A320 Knowledge Masterclass.

Landing an aircraft safely under low visibility conditions is one of the most critical challenges a pilot can face. Whether it’s fog, haze, or a snowstorm, maintaining the ability to distinguish the runway from its surroundings is crucial for safe operations. In this article, we’ll explore the factors that influence runway visibility, the systems in place to support us during low visibility landings, and the key design features that ensure these operations are as safe as possible.

Let’s dive right in.

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Insights at a Glance:

• The Science of Visibility: How airborne particles affect runway visibility.

• Lighting Systems: The role of approach lighting and runway edge lights in enhancing visibility during low visibility operations.

• Pilot Seat Position and Visibility: How even small adjustments in seat position can drastically improve safety during low-visibility landings.

• Aerodynamic Design Impact: How aircraft design and attitude affect forward visibility, especially during final approach and landing.

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Visibility Basics

Visibility during landings is heavily reliant on the contrast between the runway and its surroundings. Factors such as airborne particles—water droplets, fog, or snow—scatter and diffuse light, reducing contrast and making it harder for us to distinguish the runway. This is particularly evident when landing into the sun or when using landing lights in conditions like snow or fog. The reduction in contrast makes it difficult to identify crucial features such as a snow-covered runway or those in brightly lit urban areas.

In conditions of poor visibility, such as haze or fog, the scattering of light reduces the ability to distinguish the runway's features from the environment, which can make landing decisions more complex.

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Approach Lighting Systems

Approach lighting systems are essential tools for us to navigate low-visibility conditions, ensuring we can safely identify the runway and align ourselves properly during final approach.

Calvert 3-Bar High-Intensity Approach Lighting Design

One of the most commonly used approach lighting systems is based on the Calvert 3-bar high-intensity design, often found at regional airports. This system provides critical guidance during low-visibility approaches, where our ability to visually distinguish the runway from its surroundings may be significantly reduced due to fog, haze, or darkness.

The Calvert 3-bar system typically features a series of high-intensity lights arranged in three bars that extend out from the runway threshold. As the aircraft approaches, these lights help us maintain the correct approach path by acting as visual markers. The bars serve two purposes:

1. Guidance for Correct Path: The lights are strategically placed to ensure we remain on the proper glide path. This is especially vital during low visibility, when visual references to the ground or runway edges may be difficult to distinguish.

2. Runway Identification: These lights assist us in identifying the runway more clearly. Without such systems, distinguishing between the runway and the surrounding terrain, particularly in hazy or foggy conditions, can be extremely challenging.

This system is especially valuable because it offers a robust solution in areas where complex and expensive systems like the ILS are not available.

Calvert 3-bar system

US Approach Light System with Sequenced Flashing Lights

In addition to the Calvert system, the US approach light system (ALS) is another common system used to support us in low-visibility operations. This system features sequenced flashing lights, which are arranged in a specific pattern along the approach path.

The sequenced flashing lights serve a dual purpose:

• Simplified Approach: They act as a simplified approach system by offering clear visual guidance along the final approach. The flashing pattern helps us visually confirm our position on the glide path and assures us that we are on track to land safely.

• Enhanced Visibility: By flashing in a sequence, these lights are more noticeable, cutting through haze or fog where steady lights might blend into the surrounding environment. The flashing effect makes the approach path stand out more clearly, reducing the likelihood of confusion or misalignment during critical phases of the landing.

US ALSF-II HIALS

Runway Centerline Lights: A Visual Cue for Distance

As the aircraft approaches the runway, the centerline lights become a crucial visual cue for distance and alignment. At around 600 meters, the lights change from white to alternating red and white, signaling the aircraft is getting closer and requiring increased attention. As the aircraft reaches 300 meters, the lights turn solid red, indicating the final approach phase, confirming the aircraft is within the landing zone and preparing for touchdown.

Runway Edge Lights

Runway edge lights, which mark the lateral boundaries of the runway, are typically white. However, in the final 600 meters, these lights are sometimes highlighted with amber lights for better visibility during low-visibility conditions.

For ILS Cat 2 and Cat 3 operations, runway lights are set to high brightness to support the use of autopilot and autoland functions during low-visibility landings. We must stay alert for potential interference from the Instrument Landing System and should be ready to disconnect the autopilot if any disturbances are detected near the ground.

Taxiway Lights