approachlight

An approach light, or approach lighting system (ALS), is a lighting arrangement installed on the approach end of a runway to provide visual guidance to pilots during the final approach, especially in low visibility. Its main purpose is to help establish and maintain the correct flight path and runway alignment as pilots transition from instrument guidance to the visual environment.

A typical approach lighting system extends along the extended runway centerline from the threshold and includes a sequence of lights that may be steady-burning, crossbar lights, and sequenced flashing lights. Together these elements create a visual cue that helps pilots judge distance to the runway and align with the runway centerline. Some configurations also incorporate runway alignment indicator lights and, in certain installations, omnidirectional approach lights to aid awareness when on final approach from off-axis angles.

Several standard configurations are used in practice. In the United States, common formats include ALSF-1 and ALSF-2 (Approach Lighting System with Sequenced Flashing Lights), MALSR (Medium-intensity Approach Lighting System with Runway Alignment Indicator Lights), MALSF (Medium-intensity Approach Lighting System with Sequenced Flashing Lights), SSALR (Simplified Short Approach Lighting System with Runway Alignment Indicator Lights), and ODALS (Omnidirectional Approach Lighting System). International implementations follow ICAO guidelines, but exact layouts and light intensities vary by runway, instrument approach category, and national regulations.

Approach lighting systems are maintained as part of airport operations and are designed to operate in concert with other navigation aids, such as the ILS, to support safe landings in adverse weather or reduced visibility.