What is the correct procedure when servicing aircraft hydraulic systems regarding fluid type?

Using the manufacturer-specified fluid is critical when servicing aircraft hydraulic systems due to several key reasons. Each type of hydraulic fluid is formulated with specific properties suited to the operational requirements of the aircraft systems, including temperature ranges, chemical stability, and lubricating capabilities.

Manufacturers design hydraulic systems with a particular fluid in mind, which ensures optimal performance, safety, and reliability. Using the specified fluid helps to maintain the system's integrity and reduces the risk of contamination or chemical reactions that could occur if an unsuitable fluid is used. These reactions might lead to degraded performance, possible system failures, or even hazardous situations during flight operations.

Additionally, different hydraulic fluids may have varying viscosities and chemical compositions, which can affect the system's ability to operate under extreme conditions. Adhering to the manufacturer's guidelines ensures that all the hydraulic components work effectively and that the system meets safety standards.

The other options present significant risks and do not align with accepted practices in aircraft maintenance. Mixing fluids or using an unspecified fluid can compromise system performance and safety, while continuing with the same fluid type as previous servicing does not account for possible changes in fluid formulation or compatibility over time.