Final answer:
A pilot can descend below MDA or continue below DA/DH when they have adequate visibility, sight of the runway environment, and can execute a normal landing approach. These rules ensure safe landings in low-visibility conditions.
Step-by-step explanation:
A pilot may descend below Minimum Descent Altitude (MDA) or continue an approach below the Decision Altitude (DA) or Decision Height (DH) only if certain conditions are met. According to instrument flying rules, the pilot must have the required visibility and a view of the runway environment, which includes items like the threshold, threshold markings, threshold lights, runway end identifier lights, visual approach slope indicator, and runway or runway markings. Additionally, the aircraft must be in a position to make a normal approach to land and have the required flight visibility for the approach being flown.
These regulations ensure that a pilot does not descend to an altitude where it would be unsafe to continue the approach if visual reference with the runway cannot be maintained. Safety during the final stages of an instrument approach is paramount, and thus these requirements are strictly enforced to avoid the risks associated with low-visibility landings.