What is the primary effect of increased altitude on aircraft performance?

Increased altitude has a significant impact on aircraft performance, primarily due to the decrease in air density as altitude increases. This less dense air results in decreased engine performance because combustion processes rely on the availability of oxygen; with less oxygen, engines do not perform optimally. Additionally, lift is generated by the pressure differences caused by airflow over the wings, which is directly affected by air density. As the air becomes less dense, the wings have a harder time generating the required lift. Therefore, at higher altitudes, both the engine performance and the lift generated by the wings suffer, leading to a reduction in overall aircraft performance. Understanding this effect is critical for pilots when planning flights at higher altitudes, as they need to account for the diminished lift and reduced engine output.