Flashing LED lights play a critical role in approach lighting systems at airports, especially in low-visibility conditions such as fog, heavy rain, or snow. Their primary function is to guide pilots safely towards the runway by providing a highly visible and structured lighting pattern.

One of the key applications of flashing lights in airfield ground lighting is in the Approach Lighting System (ALS). This system is designed to help pilots transition from instrument-based navigation (used when flying in clouds or poor visibility) to visual navigation for landing. Flashing lights, often referred to as sequenced flashing lights or strobe lights, are installed in a line extending outward from the runway threshold, typically up to several hundred meters. These lights flash in a timed sequence, creating a “running” effect that leads the pilot’s eyes toward the runway.

The most prominent example of this system is the Sequenced Flashing Lights (SFL), which are part of high-intensity approach lighting systems such as the ALSF-1 and ALSF-2 used in precision instrument runways. These bright, sequential flashes are particularly effective in conditions where the static lights of the approach system may blend into fog or haze. By creating a dynamic, pulsating visual cue, they make it easier for pilots to locate the correct approach path and align with the runway centerline.

In low visibility situations, when a pilot may not yet be able to see the actual runway, these flashing lights serve as a crucial reference point, helping them maintain the correct approach angle and speed. They are particularly useful during Category II and III Instrument Landing System (ILS) approaches, where pilots may need all available visual assistance to complete a safe landing.

What does ICAO say?

ICAO’s Annex 14, Volume I – Aerodrome Design and Operations outlines the specifications for approach lighting, including sequenced flashing lights used in precision approach runways.

Approach Lighting Configuration
ICAO defines different approach lighting systems based on runway categories:

• • CAT I Runways: Require a standard approach lighting system (e.g., simple steady-burning lights).
  • CAT II & III Runways: Require High-Intensity Approach Lighting Systems (HIALS) such as ALSF-1 and ALSF-2, which include Sequenced Flashing Lights (SFL). These high-intensity flashing lights extend beyond the steady approach lights to improve visibility.

Sequenced Flashing Lights (SFL) in ICAO Standards

• • • Installed in a straight line along the extended runway centerline, usually up to 900 meters.
    • Flash in sequence, moving towards the runway threshold, creating a “guiding path” effect.
    • Must be synchronized with precise timing to provide an effective visual reference for pilots.
    • Used in conjunction with steady-burning approach lights to enhance depth perception in poor visibility.

Flashing Lights for Runway Alignment

• • • • ICAO mandates that flashing approach lights be clearly visible even in fog, heavy rain, or snow.
      • They help pilots maintain correct alignment and descent during Instrument Landing System (ILS) approaches.
      • Their effectiveness in preventing go-arounds or missed approaches is critical, especially in low-visibility (CAT III) operations.

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