Definition
A fire-resistant phosphate-ester hydraulic fluid used in most large transport-category aircraft hydraulic systems. It is highly effective at transmitting hydraulic pressure at high temperatures without igniting, but it is chemically aggressive: it attacks paint, many plastics, natural rubber seals, and human skin and eyes, and it is incompatible with petroleum-based hydraulic fluids.
Plain English
A special purple-coloured hydraulic fluid used in airliners. It resists catching fire, which is why it's used in aircraft, but it eats through paint and skin and must be handled carefully.
Context Anchor
Seen in aircraft maintenance, especially when servicing hydraulic reservoirs, checking fluid compatibility, or cleaning up hydraulic fluid leaks.
Derivation
Skydrol is a brand name originally developed by Monsanto (now produced by Eastman) in the 1940s. The name combines 'sky' (aviation use) with a chemical-product suffix. It became so widely used that the brand name is now often used informally to mean any phosphate-ester aviation hydraulic fluid, similar to how 'Hoover' is used for vacuum cleaners.
Why Pilots Care
Using the correct fire-resistant hydraulic fluid reduces the risk of fire in the event of a system leak or rupture.
Intuition Check
Skydrol does not mean any hydraulic fluid used in an aircraft. It means a specific fire-resistant hydraulic fluid type that must match the aircraft’s approved servicing instructions.
Example Sentence 1
The technician wore gloves and eye protection while servicing the hydraulic reservoir, since Skydrol can cause skin and eye irritation.
Example Sentence 2
Skydrol must be handled with care because it can damage certain paints and seals on the aircraft.