Definition
The instruments and equipment a pilot uses to determine and maintain aircraft heading by reference to magnetic north or, in some installations, true north. In light aircraft this typically includes the magnetic compass and the heading indicator (directional gyro); in more advanced aircraft it can include slaved gyro systems, flux gates, and electronic heading sources integrated into the flight display.
Plain English
The set of cockpit instruments that tell the pilot which direction the aircraft is pointing.
Context Anchor
Seen in instrument flying when learning how the aircraft shows direction on the instrument panel.
Derivation
Compass comes from the Latin com- (together) and passus (step or pace), originally meaning to measure or mark out by stepping. The sense of a direction-finding instrument grew from this idea of measuring out a path. Knowing direction is the first step of navigation, which is why these instruments are grouped together as a system.
Why Pilots Care
Reliable heading information is required to maintain course, execute turns, and navigate safely when outside visual references are lost.
Intuition Check
Do not assume compass systems means only the simple magnetic compass. In this context, it means the aircraft’s direction-indicating equipment as a whole.
Example Sentence 1
Before takeoff, the pilot aligned the heading indicator with the magnetic compass to make sure both compass systems agreed.
Example Sentence 2
In the preflight check the instructor verified that all compass systems were aligned and slaved correctly.