Definition
A gyroscopic flight instrument that displays the airplane's heading relative to a manually set reference, typically magnetic north. Because the gyro itself does not seek north, the pilot must periodically align it with the magnetic compass to correct for gyroscopic drift.
Plain English
An instrument that shows which direction the airplane is pointing. It uses a spinning gyro to give a steady reading, but the pilot has to set it to match the compass and reset it now and then because it slowly drifts.
Context Anchor
Seen on the instrument panel during taxi, before takeoff, and in flight when the pilot needs a clear heading reference.
Derivation
From Greek gyros, meaning 'circle' or 'turn.' A gyro is a spinning wheel whose stable axis is used as a reference. 'Directional' simply means it shows direction. Knowing the root reinforces that the instrument's accuracy depends on a wheel spinning steadily inside it.
Why Pilots Care
Provides a stable heading reference that does not swing or lag during turns and taxiing, unlike the magnetic compass.
Intuition Check
Do not assume the directional gyro is the same as the magnetic compass. The compass senses Earth’s magnetic field; the directional gyro shows heading from its spinning internal reference and must be set and checked against the compass.
Example Sentence 1
Before taxiing onto the runway, the pilot aligned the directional gyro with the magnetic compass so the heading indication would be accurate for departure.
Example Sentence 2
After lining up for takeoff, the pilot used the directional gyro to maintain a precise heading during the initial climb.