Answer: No, runways are not flat. They are crowned to help drain water off the sides during rain, and often one end of a runway is higher or lower than the other. When preparing takeoff performance calculations, pilots include the slope of the runway.

Runways often appear "wavy" or shimmering due to a phenomenon known as "heat haze" or "mirage," caused by the refraction of light through layers of air at different temperatures. Because runway asphalt is dark, it absorbs a tremendous amount of solar radiation, becoming much hotter than the surrounding air. This heats the layer of air directly above the pavement, making it less dense than the cooler air higher up. As light passes through these different densities, it bends (refracts), creating the shimmering, watery effect that makes a perfectly flat runway look like it has waves or puddles on it. On a structural level, runways also have a deliberate crown or camber (a slight curve from the center to the edges) to ensure water runoff during rain, and long runways may follow the natural curvature and topography of the earth. In 2026, advanced pilot HUDs (Head-Up Displays) and Enhanced Vision Systems help "see through" this heat distortion during takeoff and landing, ensuring that what looks wavy to the human eye is clearly defined as a flat, safe surface for the aircraft.