Definition
A petroleum-derived hydraulic fluid, typically MIL-H-5606, used in many general aviation aircraft hydraulic systems. It is dyed red, has a kerosene-like odor, and is chemically compatible with synthetic rubber seals. It transmits force through the hydraulic system while also lubricating components and protecting against corrosion.
Plain English
A red, oil-based fluid made from petroleum that aircraft hydraulic systems use to push and move things like landing gear, brakes, and flaps.
Context Anchor
Seen when studying aircraft hydraulic systems, checking a maintenance manual, or reading a service placard near a hydraulic fluid reservoir.
Derivation
‘Mineral-based’ refers to the fluid being refined from mineral oil, which is itself derived from petroleum (an underground mineral resource). The term distinguishes this type from synthetic-based fluids like Skydrol, which are chemically engineered rather than refined from crude oil.
Why Pilots Care
Using the incorrect fluid type can damage seals, cause leaks, or lead to hydraulic system failure.
Intuition Check
“Mineral-based” does not mean the fluid contains grit, minerals, or water. In this context, it means petroleum-oil based, and compatibility with the aircraft’s hydraulic system matters.
Example Sentence 1
Before adding fluid to the reservoir, the mechanic confirmed the system used mineral-based hydraulic fluid by checking the placard and the red color.
Example Sentence 2
Before flight the pilot confirmed the reservoir contained the proper mineral-based hydraulic fluid specified in the aircraft manual.