Which of the following factors can reduce engine power in an aircraft?

Higher temperatures can reduce engine power in an aircraft due to the effect of temperature on air density and, consequently, engine performance. As the temperature increases, the density of the air decreases, resulting in less oxygen being available for the combustion process in the engine. This reduction in oxygen leads to a decrease in power output, as the engine relies on a proper air-fuel mixture for optimal performance.

In hotter conditions, the performance of both internal combustion engines and turbocharged engines can be adversely affected because the less dense air entering the engine means that less fuel can also be introduced for combustion. This is particularly critical in high-performance aircraft where power management is essential for safe operations.

In contrast, higher fuel quality generally enhances performance, as better fuel can lead to more efficient combustion. Increased humidity might also lower performance to some extent but not as significantly as increased temperatures, which have a direct and pronounced effect on air density. Decreased altitude generally improves engine performance due to increased air density, allowing for a better air-fuel mixture and more efficient engine operation.