Sequenced Flashing Lights (SFL)

Sequenced Flashing Lights (SFLs) are a series of bright flashing lights that are part of an Approach Lighting System (ALS) and help pilots align and approach a runway correctly, especially in poor visibility. They are often referred to as the "rabbit" because of their distinctive flashing pattern.

1. Features of SFL

✅ Bright white flashing light → Placed in front of the runway and flashes in a sequence towards the runway .
✅ Walk in a pattern to the landing zone → Create a moving effect that helps the pilot track the landing direction .
✅ Flashing Speed & Sequence → Each light flashes in sequence , creating an illusion of movement towards the runway.
✅ Used in low visibility (fog, rain, night) → Provides extra depth and visibility .
✅ Often combined with other ALS components such as ALSF-1, ALSF-2 and MALSR .

2. How do Sequenced Flashing Lights work?

🔹 Lights are placed before the runway → At distances of 300 to 900 meters in the approach zone.
🔹 Flashing in a fixed sequence → The closest light flashes last, creating a moving effect .
🔹 Guides the pilot to the correct landing position → Especially useful in dark or foggy conditions .
🔹 Flash rate adjusted to the speed of the aircraft → Normally twenty flashes per second .

3. Benefits of SFL

✈ Improves runway visibility → Especially at night and in bad weather .
🚀 Provides a visual reference → Pilots can better estimate the exact direction and distance to the runway .
🌫 Increases safety in low visibility → Supports landings in fog and rain .
🎯 Helps pilots with alignment → Prevents deviations and incorrect landing angles.

4. Where are SFLs used?

SFLs are often found at large airports and military airfields that have precision approach routes, especially at:
✅ Instrument Landing Systems (ILS) → Used in category CAT I, CAT II and CAT III landings .
✅ Approach Lighting System ALSF-1 and ALSF-2 → Standard at major international airports .
✅ MALSR systems → At regional airports with medium visibility conditions .
✅ Military airports → For fast and accurate approaches in various weather conditions.

5. Difference between SFL and other ALS components

💡 In short:
Sequenced Flashing Lights (SFL) are bright flashing lights that visually guide the pilot to the runway , especially in poor visibility . They create a moving light effect toward the runway, improving the safety and precision of landings .