What role does runway slope have in aircraft performance?

Runway slope plays a significant role in aircraft performance, particularly affecting takeoff and landing distances. When it comes to an uphill slope, it increases the takeoff distance required for an aircraft to become airborne. This is because the aircraft must overcome the additional gravitational force acting against it due to the incline. As the plane rolls up a slope, it needs more speed and longer distance to generate enough lift, thereby increasing the amount of runway needed compared to a flat or downhill surface.

Conversely, a downhill slope would assist an aircraft during takeoff as it would benefit from the gravitational pull, reducing the distance required to reach takeoff speed. In a similar manner, a flat runway is indeed advantageous since it allows for optimal aircraft performance without the added factors of elevation change.

In summary, the uphill slope increases the takeoff distance required, which aligns with the chosen answer.