Which pair correctly identifies two common types of hydraulic fluid?

• A. Mineral and Synthetic
• B. Mineral and Water
• C. Synthetic and Alcohol
• D. Oil and Gas

Answer: (A)

Hydraulic fluids mainly come in two base categories: mineral oil–based and synthetic. Mineral oil fluids are petroleum-derived, inexpensive, and widely used because they lubricate well and tend to be compatible with many seals and components. Synthetic hydraulic fluids, on the other hand, are designed for tougher conditions—they offer higher fire resistance and better stability at high temperatures, which is why they’re chosen for systems where safety and performance matter in extreme environments.

Other options like water-based or alcohol-based fluids exist in some niche or specialized systems, but they’re not as common in aviation hydraulics due to issues such as corrosion risks, seal compatibility, and performance under varying temperatures. Oil and gas isn’t a standard way to categorize hydraulic fluids, so it doesn’t fit as a common type. That’s why the pair mineral and synthetic best identifies the two main, commonly used categories.