Definition
An instrument that indicates direction relative to magnetic north by means of a magnetized element that aligns itself with the Earth's magnetic field. In an airplane, the magnetic compass is a self-contained, liquid-filled instrument that displays heading on a rotating card visible through a small window, and it serves as the primary backup heading reference required by regulation.
Plain English
A direction-finding instrument that uses the Earth's magnetism to show which way the airplane is pointing.
Context Anchor
Seen on the instrument panel and used when checking or maintaining a heading during straight flight.
Derivation
From the Old French 'compas,' meaning a circle or measured step, which itself comes from Latin 'com-' (together) and 'passus' (step or pace). The original sense was 'to step out a circle.' That circular idea carried into the navigation instrument, since a compass card is a 360-degree circle of directions.
Why Pilots Care
Provides the primary reference for directional control and heading maintenance when outside visual cues are limited or absent.
Intuition Check
A compass does not show where the airplane is going over the ground; wind can make the actual path different. It shows the direction the airplane’s nose is pointed, referenced to magnetic north.
Example Sentence 1
After leveling the wings, the pilot glanced at the compass to confirm the airplane was tracking 270 degrees as planned.
Example Sentence 2
After leveling the wings, the pilot cross-checked the compass to confirm the airplane had returned to the assigned course.