When is it permissible to descend below MDA/DA?

Descending below Minimum Descent Altitude (MDA) or Decision Altitude (DA) is permissible only when the runway environment is in sight. This is a critical aspect of aviation safety regulations, which are designed to ensure that pilots can visually confirm that they are on the correct flight path to land safely.

When the runway environment is in sight, it usually means that pilots can adequately recognize specific visual cues such as the runway lights, runway itself, or other identifiable features that confirm they are approaching the intended landing area. This visibility allows pilots to assess the situation in front of them and ensures they can safely continue their approach and landing.

The alternatives involve conditions that do not meet the criteria for safety when descending below MDA or DA. For instance, engaging the autopilot does not change the requirement for visual confirmation of the runway. Similarly, clearance from air traffic control is inadequate without visual references, as it does not guarantee a safe landing perspective. Descending over populated areas doesn't provide justification unless the runway is clearly visible, which again ties back to the necessity of visual confirmation for a safe approach. Therefore, the key point is that visual contact with the runway environment is fundamental to descending below these altitude constraints.