What is the significance of an Approach Light System in descent below MDA/DH?

The Approach Light System plays a crucial role in providing visual reference to pilots during the final stages of an approach and landing. Specifically, it is significant for descent below Minimum Descent Altitude (MDA) or Decision Height (DH) because its visibility can indicate that the pilot is on a proper flight path and safely positioned to continue the descent toward landing.

When the approach lights are clearly visible, especially within 100 feet above the Touchdown Zone Elevation (TDZE), they signify that the aircraft is aligned correctly with the runway and that the conditions are visually adequate for a landing. If the approach lights are not visible, pilots may lack the necessary visual cues to safely continue their descent, potentially leading to unsafe situations.

This understanding underscores the importance of the Approach Light System in aiding pilots to make informed decisions during critical phases of flight, particularly in low visibility situations. Thus, the necessity for approach lights to be visible below 100 feet reinforces their role as a key visual aid in the approach and landing process.