How does altitude generally affect engine performance?

The correct answer highlights that as altitude increases, engine efficiency and performance may decrease primarily due to lower air density. At higher altitudes, the air becomes less dense, which impacts the amount of oxygen available for combustion in the engine. Since engines depend on oxygen to burn fuel and generate thrust, this reduced air density can lead to a decrease in overall engine performance.

Engines typically generate less thrust and can experience a reduction in power output, which is crucial for maintaining performance during flight. This relationship between altitude and engine performance is particularly significant in piston engines and turbocharged engines, where air density plays a critical role in the combustion process.

In contrast, lower altitudes provide a denser air mass, allowing engines to perform more efficiently due to the greater availability of oxygen, which supports better combustion and overall engine output. Understanding this principle is essential for pilots to manage flight performance effectively at various altitudes.