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 low-visibility conditions. The presence, type, and operational status of the ALS directly affect the minimum visibility required to land from an instrument approach.
Plain English
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.
Context Anchor
Seen on instrument approach charts and in inoperative-components notes. If the ALS is not working, the visibility required for that approach may increase.
Why Pilots Care
An operational ALS allows lower landing minimums; when it is inoperative, visibility or ceiling requirements increase and the approach may become unusable.
Intuition Check
Do not think of the ALS as just ordinary runway edge lighting. The ALS is the light pattern before the runway that helps guide your eyes to the runway during the final part of the approach.
Example Sentence 1
Breaking out at minimums, the pilot picked up the approach lighting system and continued visually to the runway.
Example Sentence 2
With the approach lighting system reported inoperative, the published minimums increased by one-quarter mile.