Private Pilot Private Practice Exam

High humidity decreases aircraft performance primarily due to the impact it has on engine efficiency, lift, and drag. When humidity levels are high, the air density is lower because water vapor is less dense than the nitrogen and oxygen that make up the bulk of dry air. This lower density means that there are fewer air molecules available for the wings to generate lift, which can reduce an aircraft's lift capability, particularly at takeoff and climb.

Additionally, the effects of humidity can be detrimental to engine performance. Aircraft engines typically perform optimally in denser air, and when humidity is high, they may not produce as much power as they would in drier conditions. This can affect the overall performance during critical phases of flight, such as takeoff and landing, where both lift and engine thrust are vital for safe operations.

In summary, high humidity negatively affects an aircraft's performance by reducing lift due to lower air density and potentially impacting engine thrust, leading to a decrease in overall efficiency and performance capabilities.