ALS should be operated between sunrise and sunset under which condition?

• A. Prevailing visibility is 5 miles or less, or ceiling is less than 1,000 feet
• B. Prevailing visibility is 6 miles or more
• C. Ceiling is above 3,000 feet
• D. Never operate during daylight

Answer: (A)

This question is about when the airfield lighting system (ALS) should be restricted to daylight hours. The rule kicks in under marginal weather: if the prevailing visibility is 5 miles or less, or the ceiling is less than 1,000 feet, you should operate the ALS only between sunrise and sunset. The idea is to ensure pilots can rely on visible lighting cues in daylight when conditions are not favorable for flight—daylight helps distinguish lights and runway guidance in reduced visibility. When weather improves (visibility more than 5 miles and ceilings at or above 1,000 feet), there’s no longer the daylight-only restriction, so the ALS can be used outside daylight hours as appropriate.