Maintaining Skydrol Hydraulic Fluid

Nowhere in an aircraft maintenance manual is there a stated time interval for changing hydraulic fluid.

Skydrol is a hydraulic fluid that is a formulated package of chemical additives dissolved into a fire-resistant phosphate ester base stock. The additives serve different functions such as inhibiting corrosion, boosting viscosity, and preventing erosion damage to servo valves. But the most important additive related to maintenance is the one that controls acidity in the fluid. This is the only additive that is consumed while the aircraft is flying, and it is the additive that defines fluid life. Once the acid control additive is gone, the fluid has reached the end of its useful life and must be replaced. Care must be taken by maintenance personnel to prevent, detect, and, if necessary, remedy contamination that may occur within the hydraulic system.

Change Intervals

Maintaining Key Fluid Properties

The Problem with Acidity

Catching Small Problems before They Become Big Problems


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