Plain English Meaning

A pattern of bright lights leading up to the runway that helps a pilot see and line up with the runway when breaking out of clouds or low visibility.

Full Definition

An approach lighting system (ALS) is a configuration of high-intensity lights arranged in a specific pattern extending outward from the runway threshold along the extended runway centerline. It provides a visual reference that allows the pilot to transition from instrument flight to visual flight for landing, particularly in . The presence, , and of the ALS directly affect the minimum visibility required to land from an .