What characteristic does the principle hydraulic fluid used in military aircraft have?

The principle hydraulic fluid used in military aircraft is dyed red for identification purposes, which aids in safety and maintenance practices. The distinct red coloring is a universal standard that helps personnel quickly recognize the fluid, distinguishing it from other fluids, such as fuel, oil, or water, that may also be present in the aircraft environment. This identification is critical to prevent cross-contamination and ensure proper handling during maintenance and emergency situations.

While it could be that some hydraulic fluids may appear green, especially in certain applications, this is not a universal characteristic of all military hydraulic fluids. Hydraulic fluids are typically not water-based as they must provide effective lubrication and pressure transmission without the limitations that water would impose. Also, having a low flash point is undesirable, as it could lead to increased fire hazards in an aircraft's operational environment. Thus, the red dye serves a functional purpose beyond mere aesthetics, focusing on safety and effective identification in demanding operational conditions.