What is the purpose of an Approach Lighting System (ALSF/ALSF-1/ALSF-2, etc.)?

• A. To identify the runway threshold.
• B. To provide vertical guidance on approach.
• C. To transmit METAR weather data.
• D. To help pilots visually acquire the runway on approach.

Answer: (D)

Approach Lighting Systems give pilots a visual lead from the instrument portion of the approach to the runway, helping them see and align with the runway environment as they near the airfield. The lights extend outward from the runway and combine steady and sequenced flashing elements to create a bright, continuous path that guides the eyes toward the touchdown zone, making it easier to acquire the runway visually in low visibility or at night. This helps with alignment but does not provide vertical guidance—that role belongs to systems like the ILS glideslope, PAPI, or VASI. It also isn’t about transmitting weather data or identifying the threshold itself; those tasks are handled by other systems and indicators.