On an instrument approach where a DH or MDA is applicable, when may the pilot not operate below the specified altitude?

In an instrument approach, the decision height (DH) or minimum descent altitude (MDA) represents the lowest altitude a pilot may descend to during the approach under instrument flight rules. The pilot must not operate below this specified altitude unless they have the necessary visual references to continue the descent safely.

Operating below the designated DH or MDA requires specific visual references as defined by regulations. If a stabilized descent is not achievable—meaning that the aircraft cannot maintain a controlled, consistent path towards the runway—then it is unsafe to proceed below these altitudes. This situation might arise due to turbulence, equipment failure, or other factors that hinder the pilot's ability to maintain control over the descent.

While the visibility conditions and the presence of approach lights are important factors, the key aspect of safely descending below DH or MDA is the ability to conduct a stable descent. Therefore, the option reflecting that a pilot should not operate below these altitudes when a stabilized descent is not possible is the most pertinent and correct response.