What is considered a contaminated runway?

A contaminated runway is defined as one where more than 25% of the surface area is covered by a substance that can adversely affect aircraft performance, such as water, ice, snow, or slush. The correct answer specifies that this contamination occurs when more than 25% of the runway surface has more than 1/8 inch of water, which is significant enough to reduce friction and increase the risk of hydroplaning. This threshold is critical for pilots to consider during landing and takeoff to ensure safe aircraft operations.

The other options do not meet the definition of a contaminated runway. For instance, having less than 1/8 inch of water present does not typically impair performance to the same extent, and terms like "completely dry" or "no visible moisture" do not indicate contamination at all. Therefore, the correct option correctly reflects the conditions that lead to a runway being classified as contaminated and emphasizes the importance of recognizing such conditions for safety.