Definition
A clear, low-viscosity liquid (typically a refined kerosene or light petroleum-based fluid) that fills the bowl of a magnetic compass. It dampens the swing of the compass card so it settles quickly to a steady heading, and it supports the weight of the card to reduce wear on the pivot.
Plain English
The liquid inside the magnetic compass. It keeps the spinning card from swinging wildly so the heading reading settles quickly and stays readable in turbulence.
Context Anchor
Seen during compass inspection, preflight checks, and maintenance when looking for leaks, bubbles, or a compass card that does not settle normally.
Derivation
Compass comes from older words meaning to go around or measure a course. Fluid comes from the Latin word fluere, meaning to flow. Together, the term points to the flowing liquid used inside the compass to help the direction display move smoothly.
Why Pilots Care
Prevents erratic or delayed compass indications that could mislead heading control, especially in turbulence.
Grounding Statement
When the aircraft moves or vibrates, the compass fluid slows the compass card so it can settle instead of wobbling constantly.
Intuition Check
Compass fluid is not ordinary water, and it is not a liquid that powers the compass. It is a sealed damping liquid inside the instrument that helps the magnetic compass move smoothly and settle steadily.
Example Sentence 1
During the inspection, the technician noticed a small bubble in the compass and added compass fluid to top off the bowl.
Example Sentence 2
A small leak of compass fluid appeared on the instrument panel after the rough landing.