When is the ALSF-2 Approach Lighting System with Sequence Flashing used?

The ALSF-2 Approach Lighting System with Sequence Flashing is specifically designed to assist pilots during low visibility conditions, particularly for approaches categorized under Category II and Category III. These categories refer to the levels of precision and visibility required for landing, with Category II and III being used when visibility is significantly reduced due to adverse weather conditions.

The sequence flashing aspect of the ALSF-2 provides visual cues to the pilots as they approach the runway, helping them to maintain proper alignment and descent path even when they cannot see the runway or its surroundings clearly. This system is crucial when transitioning from instrument flight to a visual approach at such low visibility levels, as it enhances the pilots' spatial orientation and aids in landing safely.

In contrast, operations under visual flight rules, Category I conditions, and all types of landings do not specifically necessitate the specialized capabilities provided by the ALSF-2. Category I operations typically involve greater visibility, where standard lighting systems suffice. Hence, the requirement for a system like ALSF-2 becomes critical only for the more challenging conditions defined in Categories II and III.