What is a key visual reference for descending below MDA/DA?

The approach light system serves as a critical visual reference for pilots when descending below the Minimum Descent Altitude (MDA) or Decision Altitude (DA) during an approach. This system is designed to provide pilots with a visual guide that aids in identifying the runway environment and enhances situational awareness as they prepare to land. When pilots see the approach lights, it indicates that they are nearing the runway and that they can continue their descent, assuming other criteria are met.

In an environment where visibility might be limited, these lights assist in confirming the necessary visual references for a safe landing. Other options, such as cloud base, runway length, and weather conditions, may present important information about the flight or landing environment but do not specifically serve as the designated visual reference for descending past MDA/DA.