What does ALS refer to in the context of approach lights?

The term ALS, which stands for Approach Lighting System, refers specifically to a lighting system that provides guidance to pilots as they approach the runway for landing. It is crucial for enhancing the pilot's visual reference during low visibility conditions or at night. The requirement that it must be identifiable 100 feet above the touchdown zone is essential for ensuring that pilots can see and identify the runway environment in sufficient time to make safe landing decisions. This aspect of the approach lighting system is vital for effective visual continuous guidance during the critical phase of flight as the aircraft descends to land.