For aviation purposes, ceiling is defined as the height above the Earth's surface of the

• A. lowest layer of clouds reported as scattered, broken or thin
• B. highest layer of clouds reported as scattered, broken or thin
• C. the base of the lowest cloud in sight
• D. the altitude of the aircraft during approach

Answer: (A)

Ceiling refers to the height above the ground of the base of the lowest cloud layer that covers a significant portion of the sky. In practice this means the lowest layer described as broken or overcast (and, in some contexts, the layer described as scattered or thin if it still contributes notable sky cover). This cloud base is what limits visibility upward and is used for approach minima and flight planning. The other options don’t describe sky coverage or what restricts visibility: it isn’t the base of the lowest cloud seen, it isn’t the aircraft’s altitude on approach, and it isn’t the highest cloud layer.