Which illusion can a downsloping runway create for pilots?

When landing on a downsloping runway, pilots may experience the illusion that they are too low in their approach. This occurs because the downward slope can mislead a pilot's perception of altitude. Since the runway descends, the visual cues that normally help in judging distance and height above the ground can be distorted. The pilot might perceive that the aircraft is lower than it actually is due to the downward gradient, leading to a potential risk of flying too low and missing the correct touchdown point.

This optical illusion emphasizes the need for pilots to rely heavily on their instruments and established approach techniques rather than solely on visual judgments, especially in unusual terrain situations like a downsloping runway.