FAA Powerplant Written Practice Test

How does altitude affect the density of air in relation to engine performance?

1. It increases fuel efficiency

2. It decreases engine power due to thinner air

3. It has no effect on engine performance

4. It enhances combustion efficiency

The correct answer is: It decreases engine power due to thinner air

As altitude increases, the density of air decreases. This thinner air has a direct impact on engine performance, primarily because internal combustion engines require a specific air-fuel mixture to operate efficiently. When air density decreases, there is less oxygen available for combustion, which leads to a reduction in engine power. Specifically, engines produce less power because they cannot intake the same volume of air as they can at lower altitudes where the air is denser. Consequently, reduced air density results in a drop in the amount of oxygen available for combustion, which affects overall engine efficiency and power output. In contrast, increases in fuel efficiency or enhancements in combustion efficiency are not associated with higher altitudes due to this reduced oxygen availability. Similarly, it would be inaccurate to claim that altitude has no effect on engine performance, as numerous studies and practical experiences demonstrate the significant power loss that occurs as altitude increases.