FAA Powerplant Written Practice Test

Why is it important to change aircraft engine lubricating oils at predetermined intervals?

1. To reduce oil viscosity

2. To prevent oil leaks

3. The oil becomes contaminated with moisture and other particles

4. To enhance engine performance

The correct answer is: The oil becomes contaminated with moisture and other particles

Changing aircraft engine lubricating oils at predetermined intervals is crucial primarily because the oil can become contaminated with moisture and various particles over time. As the oil circulates through the engine, it collects byproducts of combustion, metal shavings, dirt, and moisture. Factors such as operating temperature and conditions can cause oil to degrade, leading to the formation of sludge and sediments that can impair the oil's ability to lubricate effectively. Contaminated oil can lead to increased friction between moving parts, ultimately resulting in wear and tear on the engine components. This degradation of lubricating properties can lead to overheating and potential engine failure if not addressed. Regularly changing the oil ensures that the engine maintains its proper function, minimizes long-term damage, and extends overall engine lifespan, thereby promoting operational safety and reliability. While reducing oil viscosity, preventing leaks, and enhancing performance are relevant to engine maintenance, they are more indirect or secondary benefits compared to the primary necessity of avoiding contamination. Maintaining clean oil directly addresses the engine's need for effective lubrication and operation.