How does high humidity affect takeoff performance?

High humidity plays a crucial role in aircraft performance during takeoff. When humidity is high, the amount of water vapor in the air increases, which effectively reduces the overall air density. Air density is a critical factor in determining how much lift an aircraft generates and how efficiently its engines produce thrust.

As humidity increases, the density of the air decreases because water vapor is less dense than the nitrogen and oxygen that are typically present in dry air. This reduction in air density means that the aircraft requires a longer takeoff distance to achieve the necessary speed for lift-off. The engines may not perform as efficiently as they would in denser, drier air, leading to a requirement for more runway length to reach the required takeoff speeds.

Therefore, the correct answer highlights that the reduction in air density due to high humidity results in an increase in takeoff distance, emphasizing the importance of understanding environmental conditions for effective flight planning and performance assessment.