What types of hydraulic fluids are currently authorized for use in Army aircraft?

• A. Petroleum
• B. Synthetic
• C. Petroleum and Synthetic
• D. Water-based hydraulic fluids

Answer: (C)

Hydraulic systems in Army aircraft are designed to use either petroleum-based fluids or synthetic fluids. This mix covers the different materials and operating conditions found across aircraft components. Petroleum-based fluids are reliable, cost-effective, and have long service use in many systems, while synthetic fluids provide advantages like higher temperature stability and better compatibility with certain seals and elastomers. Water-based fluids, on the other hand, do not meet the performance and durability requirements for aviation systems and are not authorized. So, the current policy allows both petroleum-based and synthetic hydraulic fluids, not just one type or water-based options.